What particles make up the nucleus of an atom. The structure of the atom: nucleus, neutron, proton, electron

As already noted, an atom consists of three types of elementary particles: protons, neutrons and electrons. The atomic nucleus is the central part of the atom, consisting of protons and neutrons. Protons and neutrons have the common name nucleon, in the nucleus they can turn into each other. The nucleus of the simplest atom, the hydrogen atom, consists of one elementary particle, the proton.

The diameter of the nucleus of an atom is approximately 10 -13 - 10 -12 cm and is 0.0001 of the diameter of an atom. However, almost the entire mass of an atom (99.95 - 99.98%) is concentrated in the nucleus. If it were possible to obtain 1 cm 3 of pure nuclear matter, its mass would be 100 - 200 million tons. The mass of the nucleus of an atom is several thousand times greater than the mass of all the electrons that make up the atom.

Proton- an elementary particle, the nucleus of a hydrogen atom. The mass of a proton is 1.6721x10 -27 kg, it is 1836 times the mass of an electron. The electric charge is positive and equal to 1.66x10 -19 C. Coulomb - a unit of electric charge, equal to the amount of electricity passing through the cross section of the conductor in a time of 1 s at a constant current strength of 1A (ampere).

Each atom of any element contains a certain number of protons in the nucleus. This number is constant for a given element and determines its physical and chemical properties. That is, the number of protons depends on what chemical element we are dealing with. For example, if one proton in the nucleus is hydrogen, if 26 protons are iron. The number of protons in the atomic nucleus determines the charge of the nucleus (charge number Z) and the serial number of the element in the periodic system of elements D.I. Mendeleev (atomic number of the element).

Hneutron- an electrically neutral particle with a mass of 1.6749 x10 -27 kg, 1839 times the mass of an electron. A neuron in a free state is an unstable particle; it independently turns into a proton with the emission of an electron and an antineutrino. The half-life of neutrons (the time during which half of the original number of neutrons decays) is approximately 12 minutes. However, in a bound state inside stable atomic nuclei, it is stable. The total number of nucleons (protons and neutrons) in the nucleus is called the mass number (atomic mass - A). The number of neutrons that make up the nucleus is equal to the difference between the mass and charge numbers: N = A - Z.

Electron- an elementary particle, the carrier of the smallest mass - 0.91095x10 -27 g and the smallest electric charge - 1.6021x10 -19 C. This is a negatively charged particle. The number of electrons in an atom is equal to the number of protons in the nucleus, i.e. the atom is electrically neutral.

Positron– an elementary particle with a positive electric charge, an antiparticle with respect to an electron. The mass of an electron and a positron are equal, and the electric charges are equal in absolute value, but opposite in sign.

Different types of nuclei are called nuclides. A nuclide is a type of atom with a given number of protons and neutrons. In nature, there are atoms of the same element with different atomic masses (mass numbers): 17 35 Cl, 17 37 Cl, etc. The nuclei of these atoms contain the same number of protons, but a different number of neutrons. Varieties of atoms of the same element that have the same nuclear charge but different mass numbers are called isotopes . Having the same number of protons, but differing in the number of neutrons, isotopes have the same structure of electron shells, i.e. very similar chemical properties and occupy the same place in the periodic table of chemical elements.

Isotopes are denoted by the symbol of the corresponding chemical element with the index A located at the top left - the mass number, sometimes the number of protons (Z) is also given at the bottom left. For example, the radioactive isotopes of phosphorus are 32 P, 33 P, or 15 32 P and 15 33 P, respectively. When designating an isotope without indicating the symbol of the element, the mass number is given after the designation of the element, for example, phosphorus - 32, phosphorus - 33.

Most chemical elements have several isotopes. In addition to the hydrogen isotope 1 H-protium, heavy hydrogen 2 H-deuterium and superheavy hydrogen 3 H-tritium are known. Uranium has 11 isotopes, in natural compounds there are three of them (uranium 238, uranium 235, uranium 233). They have 92 protons and 146.143 and 141 neutrons, respectively.

Currently, more than 1900 isotopes of 108 chemical elements are known. Of these, natural isotopes include all stable (there are approximately 280 of them) and natural isotopes that are part of radioactive families (there are 46 of them). The rest are artificial, they are obtained artificially as a result of various nuclear reactions.

The term "isotopes" should only be used when referring to atoms of the same element, for example, carbon isotopes 12 C and 14 C. If atoms of different chemical elements are meant, it is recommended to use the term "nuclides", for example, radionuclides 90 Sr, 131 J, 137 Cs.

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In some rare cases, short-lived exotic atoms can be formed, in which other particles serve as the nucleus instead of a nucleon.

The number of protons in a nucleus is called its charge number Z (\displaystyle Z)- this number is equal to the ordinal number of the element to which the atom belongs, in the table (Periodic system of elements) of Mendeleev. The number of protons in the nucleus determines the structure of the electron shell of a neutral atom and, thus, the chemical properties of the corresponding element. The number of neutrons in a nucleus is called its isotopic number N (\displaystyle N). Nuclei with the same number of protons and different numbers of neutrons are called isotopes. Nuclei with the same number of neutrons but different numbers of protons are called isotones. The terms isotope and isotone are also used in relation to atoms containing the indicated nuclei, as well as to characterize non-chemical varieties of one chemical element. The total number of nucleons in a nucleus is called its mass number A (\displaystyle A) (A = N + Z (\displaystyle A=N+Z)) and is approximately equal to the average mass of an atom, indicated in the periodic table. Nuclides with the same mass number but different proton-neutron composition are called isobars.

Like any quantum system, nuclei can be in a metastable excited state, and in some cases, the lifetime of such a state is calculated in years. Such excited states of nuclei are called nuclear isomers.

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Story

The scattering of charged particles can be explained by assuming an atom that consists of a central electric charge concentrated at a point and surrounded by a uniform spherical distribution of opposite electricity of equal magnitude. With such a structure of the atom, α- and β-particles, when they pass at a close distance from the center of the atom, experience large deviations, although the probability of such a deviation is small.

Thus, Rutherford discovered the atomic nucleus, from that moment nuclear physics began, studying the structure and properties of atomic nuclei.

After the discovery of stable isotopes of elements, the nucleus of the lightest atom was assigned the role of a structural particle of all nuclei. Since 1920, the nucleus of the hydrogen atom has had an official term - proton. In 1921, Lisa Meitner proposed the first, proton-electron, model of the structure of the atomic nucleus, according to which it consists of protons, electrons and alpha particles: 96 . However, in 1929 there was a "nitrogen catastrophe" - W. Heitler and G. Herzberg established that the nucleus of the nitrogen atom obeys Bose - Einstein statistics, and not Fermi - Dirac statistics, as predicted by the proton-electron model: 374. Thus, this model came into conflict with the experimental results of measurements of spins and magnetic moments of nuclei. In 1932, James Chadwick discovered a new electrically neutral particle called the neutron. In the same year, Ivanenko and, independently, Heisenberg put forward a hypothesis about the proton-neutron structure of the nucleus. Later, with the development of nuclear physics and its applications, this hypothesis was fully confirmed.

Theories of the structure of the atomic nucleus

In the process of development of physics, various hypotheses were put forward for the structure of the atomic nucleus; however, each of them is capable of describing only a limited set of nuclear properties. Some models may be mutually exclusive.

The most famous are the following:

Drop model nucleus - proposed in 1936 by Niels Bohr.
Shell model nucleus - proposed in the 30s of the XX century.
Generalized Bohr-Mottelson model
Cluster kernel model
Model of nucleon associations
Superfluid core model
Statistical model of the nucleus

Nuclear physics

The charges of atomic nuclei were first determined by Henry Moseley in 1913. The scientist interpreted his experimental observations by the dependence of the X-ray wavelength on a certain constant Z (\displaystyle Z), changing by one from element to element and equal to one for hydrogen:

1 / λ = a Z − b (\displaystyle (\sqrt (1/\lambda ))=aZ-b), Where

A (\displaystyle a) And b (\displaystyle b)- permanent.

From which Moseley concluded that the atomic constant found in his experiments, which determines the wavelength of the characteristic X-ray radiation and coincides with the serial number of the element, can only be the charge of the atomic nucleus, which became known as law Moseley .

Weight

Due to the difference in the number of neutrons A − Z (\displaystyle A-Z) isotopes of an element have different masses M (A , Z) (\displaystyle M(A,Z)), which is an important characteristic of the kernel. In nuclear physics, the mass of nuclei is usually measured in atomic units mass ( A. eat.), for one a. e. m. take 1/12 of the mass of the 12 C nuclide. It should be noted that the standard mass that is usually given for a nuclide is the mass of a neutral atom. To determine the mass of the nucleus, it is necessary to subtract the sum of the masses of all electrons from the mass of the atom (a more accurate value will be obtained if we also take into account the binding energy of electrons with the nucleus).

In addition, in nuclear physics, the energy equivalent mass is often used. According to the Einstein relation, each mass value M (\displaystyle M) corresponds to the total energy:

E = M c 2 (\displaystyle E=Mc^(2)), Where c (\displaystyle c) is the speed of light in vacuum.

The ratio between a. e.m. and its energy equivalent in joules:

E 1 = 1 . 660539 ⋅ 10 − 27 ⋅ (2 . 997925 ⋅ 10 8) 2 = 1 . 492418 ⋅ 10 − 10 (\displaystyle E_(1)=1.660539\cdot 10^(-27)\cdot ( 2.997925\cdot 10^(8))^(2)=1.492418\cdot 10^(-10)), E 1 = 931 , 494 (\displaystyle E_(1)=931,494).

Radius

Analysis of the decay of heavy nuclei refined Rutherford's estimate and related the radius of the nucleus to the mass number by a simple relationship:

R = r 0 A 1 / 3 (\displaystyle R=r_(0)A^(1/3)),

where is a constant.

Since the radius of the nucleus is not a purely geometric characteristic and is associated primarily with the radius of action of nuclear forces, the value r 0 (\displaystyle r_(0)) depends on the process in the analysis of which the value is obtained R (\displaystyle R), average value r 0 = 1 , 23 ⋅ 10 − 15 (\displaystyle r_(0)=1.23\cdot 10^(-15)) m, thus the core radius in meters:

R = 1 , 23 ⋅ 10 − 15 A 1 / 3 (\displaystyle R=1,23\cdot 10^(-15)A^(1/3)).

Kernel moments

Like the nucleons that make it up, the nucleus has its own moments.

Spin

Since nucleons have their own mechanical moment, or spin, equal to 1 / 2 (\displaystyle 1/2), then the nuclei must also have mechanical moments. In addition, nucleons participate in the nucleus in orbital motion, which is also characterized by a certain moment of momentum of each nucleon. Orbital moments take only integer values ℏ (\displaystyle \hbar )(constant Dirac). All mechanical moments of nucleons, both spins and orbital, are summed algebraically and constitute the spin of the nucleus.

Despite the fact that the number of nucleons in a nucleus can be very large, the spins of nuclei are usually small and amount to no more than a few ℏ (\displaystyle \hbar ), which is explained by the peculiarity of the interaction of nucleons of the same name. All paired protons and neutrons interact only in such a way that their spins cancel each other out, that is, pairs always interact with antiparallel spins. The total orbital momentum of a pair is also always zero. As a result, nuclei consisting of an even number of protons and an even number of neutrons do not have a mechanical momentum. Non-zero spins exist only for nuclei that have unpaired nucleons in their composition, the spin of such a nucleon is added to its own orbital momentum and has some half-integer value: 1/2, 3/2, 5/2. Nuclei of odd-odd composition have integer spins: 1, 2, 3, etc. .

Magnetic moment

The measurements of spins became possible due to the presence of magnetic moments directly related to them. They are measured in magnetons and for different nuclei they are from -2 to +5 nuclear magnetons. Due to the relatively large mass of nucleons, the magnetic moments of nuclei are very small compared to those of electrons, so measuring them is much more difficult. Like spins, magnetic moments are measured by spectroscopic methods, the most accurate being the nuclear magnetic resonance method.

The magnetic moment of even-even pairs, like the spin, is equal to zero. The magnetic moments of nuclei with unpaired nucleons are formed by the intrinsic moments of these nucleons and the moment associated with the orbital motion of the unpaired proton.

Electric quadrupole moment

Atomic nuclei with a spin greater than or equal to unity have non-zero quadrupole moments, indicating that they are not exactly spherical. The quadrupole moment has a plus sign if the nucleus is extended along the spin axis (fusiform body), and a minus sign if the nucleus is stretched in a plane perpendicular to the spin axis (lenticular body). Nuclei with positive and negative quadrupole moments are known. The absence of spherical symmetry in the electric field created by a nucleus with a nonzero quadrupole moment leads to the formation of additional energy levels of atomic electrons and the appearance of hyperfine structure lines in the spectra of atoms, the distances between which depend on the quadrupole moment.

Bond energy

Core Stability

From the fact that the average binding energy decreases for nuclides with mass numbers greater than or less than 50–60, it follows that for nuclei with small A (\displaystyle A) the fusion process is energetically favorable - thermonuclear fusion, leading to an increase in the mass number, and for nuclei with large A (\displaystyle A)- the process of division. At present, both of these processes, leading to the release of energy, have been carried out, the latter being the basis of modern nuclear energy, and the former being under development.

Detailed studies have shown that the stability of nuclei also depends significantly on the parameter N/Z (\displaystyle N/Z)- the ratio of the numbers of neutrons and protons. Average for the most stable nuclei N / Z ≈ 1 + 0.015A 2 / 3 (\displaystyle N/Z\approx 1+0.015A^(2/3)), therefore the nuclei of light nuclides are most stable at N ≈ Z (\displaystyle N\approx Z), and as the mass number increases, the electrostatic repulsion between protons becomes more and more noticeable, and the stability region shifts towards N > Z (\displaystyle N>Z)(see explanatory figure).

If we consider the table of stable nuclides found in nature, we can pay attention to their distribution by even and odd values. Z (\displaystyle Z) And N (\displaystyle N). All nuclei with odd values of these quantities are nuclei of light nuclides 1 2 H (\displaystyle ()_(1)^(2)(\textrm (H))), 3 6 Li (\displaystyle ()_(3)^(6)(\textrm (Li))), 5 10 B (\displaystyle ()_(5)^(10)(\textrm (B))), 7 14 N (\displaystyle ()_(7)^(14)(\textrm (N))). Among the isobars with odd A, as a rule, only one is stable. In the case of even A (\displaystyle A) often there are two, three or more stable isobars, therefore, the most stable are even-even, the least - odd-odd. This phenomenon indicates that both neutrons and protons tend to cluster in pairs with antiparallel spins, which leads to a violation of the smoothness of the above dependence of the binding energy on A (\displaystyle A) .

Thus, the parity of the number of protons or neutrons creates a certain margin of stability, which leads to the possibility of the existence of several stable nuclides, differing respectively in the number of neutrons for isotopes and in the number of protons for isotons. Also, the parity of the number of neutrons in the composition of heavy nuclei determines their ability to fission under the influence of neutrons.

nuclear forces

Nuclear forces are forces that hold nucleons in the nucleus, which are large attractive forces that act only at small distances. They have saturation properties, in connection with which the nuclear forces are assigned an exchange character (with the help of pi-mesons). Nuclear forces are spin dependent, independent of electric charge, and are not central forces.

Kernel levels

Unlike free particles, for which the energy can take on any value (the so-called continuous spectrum), bound particles (that is, particles whose kinetic energy is less than the absolute value of the potential), according to quantum mechanics, can only be in states with certain discrete energy values , the so-called discrete spectrum. Since the nucleus is a system of bound nucleons, it has a discrete energy spectrum. It is usually in its lowest energy state, called main. If energy is transferred to the nucleus, it will turn into excited state.

The location of the energy levels of the nucleus in the first approximation:

D = a e − b E ∗ (\displaystyle D=ae^(-b(\sqrt (E^(*))))), Where:

D (\displaystyle D)- average distance between levels,

E ∗ (\displaystyle E^(*)) is the excitation energy of the nucleus,

A (\displaystyle a) And b (\displaystyle b)- coefficients constant for a given kernel:

A (\displaystyle a)- average distance between the first excited levels (about 1 MeV for light nuclei, 0.1 MeV for heavy nuclei)

Long before the emergence of reliable data on the internal structure of all things, Greek thinkers imagined matter in the form of the smallest fiery particles that were in constant motion. Probably, this vision of the world order of things was derived from purely logical conclusions. Despite some naivety and absolute lack of evidence for this statement, it turned out to be true. Although scientists were able to confirm a bold guess only twenty-three centuries later.

The structure of atoms

At the end of the 19th century, the properties of a discharge tube through which a current was passed were investigated. Observations have shown that two streams of particles are emitted:

The negative particles of the cathode rays were called electrons. Subsequently, particles with the same charge-to-mass ratio were found in many processes. Electrons seemed to be universal constituents of various atoms, quite easily separated by the bombardment of ions and atoms.

Particles carrying a positive charge were represented by fragments of atoms after they lost one or more electrons. In fact, the positive rays were groups of atoms devoid of negative particles, and therefore having a positive charge.

Thompson model

On the basis of experiments, it was found that positive and negative particles represented the essence of the atom, were its constituents. The English scientist J. Thomson proposed his theory. In his opinion, the structure of the atom and the atomic nucleus was a kind of mass in which negative charges were squeezed into a positively charged ball, like raisins in a cupcake. Charge compensation made the cake electrically neutral.

Rutherford model

The young American scientist Rutherford, analyzing the tracks left after alpha particles, came to the conclusion that the Thompson model is imperfect. Some alpha particles were deflected by small angles - 5-10 o . In rare cases, alpha particles were deflected at large angles of 60-80 o , and in exceptional cases, the angles were very large - 120-150 o . Thompson's model of the atom could not explain such a difference.

Rutherford proposes a new model that explains the structure of the atom and the atomic nucleus. The physics of processes states that an atom must be 99% empty, with a tiny nucleus and electrons revolving around it, which move in orbits.

He explains the deviations during impacts by the fact that the particles of the atom have their own electric charges. Under the influence of bombarding charged particles, atomic elements behave like ordinary charged bodies in the macrocosm: particles with the same charges repel each other, and with opposite charges they attract.

State of atoms

At the beginning of the last century, when the first particle accelerators were launched, all theories explaining the structure of the atomic nucleus and the atom itself were waiting for experimental verification. By that time, the interactions of alpha and beta rays with atoms had already been thoroughly studied. Until 1917, it was believed that atoms were either stable or radioactive. Stable atoms cannot be split, the decay of radioactive nuclei cannot be controlled. But Rutherford managed to refute this opinion.

First proton

In 1911, E. Rutherford put forward the idea that all nuclei consist of the same elements, the basis for which is the hydrogen atom. This idea was prompted by an important conclusion of previous studies of the structure of matter: the masses of all chemical elements are divided without a trace by the mass of hydrogen. The new assumption opened up unprecedented possibilities, allowing us to see the structure of the atomic nucleus in a new way. Nuclear reactions had to confirm or disprove the new hypothesis.

Experiments were carried out in 1919 with nitrogen atoms. By bombarding them with alpha particles, Rutherford achieved an amazing result.

The N atom absorbed the alpha particle, then turned into an oxygen atom O 17 and emitted a hydrogen nucleus. This was the first artificial transformation of an atom of one element into another. Such an experience gave hope that the structure of the atomic nucleus, the physics of existing processes make it possible to carry out other nuclear transformations.

The scientist used in his experiments the method of scintillation - flashes. From the frequency of flashes, he drew conclusions about the composition and structure of the atomic nucleus, about the characteristics of the particles born, about their atomic mass and serial number. The unknown particle was named by Rutherford the proton. It had all the characteristics of a hydrogen atom stripped of its single electron - a single positive charge and a corresponding mass. Thus it was proved that the proton and the nucleus of hydrogen are the same particles.

In 1930, when the first large accelerators were built and launched, Rutherford's model of the atom was tested and proved: each hydrogen atom consists of a lone electron, the position of which cannot be determined, and a loose atom with a lone positive proton inside. Since protons, electrons, and alpha particles can fly out of an atom when bombarded, scientists thought that they were the constituents of any atom's nucleus. But such a model of the nucleus atom seemed unstable - the electrons were too large to fit in the nucleus, in addition, there were serious difficulties associated with the violation of the law of momentum and conservation of energy. These two laws, like strict accountants, said that the momentum and mass during the bombardment disappear in an unknown direction. Since these laws were generally accepted, it was necessary to find explanations for such a leak.

Neutrons

Scientists around the world set up experiments aimed at discovering new constituents of the nuclei of atoms. In the 1930s, German physicists Becker and Bothe bombarded beryllium atoms with alpha particles. In this case, an unknown radiation was registered, which it was decided to call G-rays. Detailed studies revealed some features of the new beams: they could propagate strictly in a straight line, did not interact with electric and magnetic fields, and had a high penetrating power. Later, the particles that form this type of radiation were found in the interaction of alpha particles with other elements - boron, chromium and others.

Chadwick's hypothesis

Then James Chadwick, a colleague and student of Rutherford, gave a short report in Nature magazine, which later became well known. Chadwick drew attention to the fact that the contradictions in the conservation laws are easily resolved if we assume that the new radiation is a stream of neutral particles, each of which has a mass approximately equal to the mass of a proton. Considering this assumption, physicists significantly supplemented the hypothesis explaining the structure of the atomic nucleus. Briefly, the essence of the additions was reduced to a new particle and its role in the structure of the atom.

Properties of the neutron

The discovered particle was given the name "neutron". The newly discovered particles did not form electromagnetic fields around themselves and easily passed through matter without losing energy. In rare collisions with light nuclei of atoms, the neutron is able to knock out the nucleus from the atom, losing a significant part of its energy. The structure of the atomic nucleus assumed the presence of a different number of neutrons in each substance. Atoms with the same nuclear charge but different numbers of neutrons are called isotopes.

Neutrons have served as an excellent replacement for alpha particles. Currently, they are used to study the structure of the atomic nucleus. Briefly, their significance for science cannot be described, but it was thanks to the bombardment of atomic nuclei by neutrons that physicists were able to obtain isotopes of almost all known elements.

The composition of the nucleus of an atom

At present, the structure of the atomic nucleus is a collection of protons and neutrons held together by nuclear forces. For example, a helium nucleus is a lump of two neutrons and two protons. Light elements have an almost equal number of protons and neutrons, while heavy elements have a much larger number of neutrons.

This picture of the structure of the nucleus is confirmed by experiments at modern large accelerators with fast protons. The electric forces of repulsion of protons are balanced by vigorous forces that act only in the nucleus itself. Although the nature of nuclear forces is not yet fully understood, their existence is practically proven and fully explains the structure of the atomic nucleus.

Relationship between mass and energy

In 1932, a cloud chamber captured an amazing photograph proving the existence of positive charged particles, with the mass of an electron.

Prior to this, positive electrons were theoretically predicted by P. Dirac. A real positive electron was also discovered in cosmic radiation. The new particle was called the positron. When colliding with its twin - an electron, annihilation occurs - the mutual annihilation of two particles. This releases a certain amount of energy.

Thus, the theory developed for the macrocosm was fully suitable for describing the behavior of the smallest elements of matter.

atomic nucleus is the central part of the atom, made up of protons and neutrons (collectively called nucleons).

The nucleus was discovered by E. Rutherford in 1911 while studying the passage α -particles through matter. It turned out that almost the entire mass of an atom (99.95%) is concentrated in the nucleus. The size of the atomic nucleus is of the order of 10 -1 3 -10 - 12 cm, which is 10,000 times smaller than the size of the electron shell.

The planetary model of the atom proposed by E. Rutherford and his experimental observation of hydrogen nuclei knocked out α -particles from the nuclei of other elements (1919-1920), led the scientist to the idea of proton. The term proton was introduced in the early 20s of the XX century.

Proton (from Greek. protons- first, character p) is a stable elementary particle, the nucleus of a hydrogen atom.

Proton- a positively charged particle, the charge of which is equal in absolute value to the charge of an electron e\u003d 1.6 10 -1 9 Cl. The mass of a proton is 1836 times the mass of an electron. Rest mass of a proton m p= 1.6726231 10 -27 kg = 1.007276470 amu

The second particle in the nucleus is neutron.

Neutron (from lat. neuter- neither one nor the other, a symbol n) is an elementary particle that has no charge, i.e., neutral.

The mass of the neutron is 1839 times the mass of the electron. The mass of a neutron is almost equal to (slightly larger than) that of a proton: the rest mass of a free neutron m n= 1.6749286 10 -27 kg = 1.0008664902 amu and exceeds the proton mass by 2.5 electron masses. Neutron, along with the proton under the common name nucleon is part of the atomic nucleus.

The neutron was discovered in 1932 by D. Chadwig, a student of E. Rutherford, during the bombardment of beryllium α -particles. The resulting radiation with high penetrating power (it overcame an obstacle made of a lead plate 10–20 cm thick) intensified its effect when passing through the paraffin plate (see figure). The Joliot-Curie estimates of the energy of these particles from the tracks in the cloud chamber, and additional observations made it possible to eliminate the initial assumption that this γ -quanta. The great penetrating power of new particles, called neutrons, was explained by their electrical neutrality. After all, charged particles actively interact with matter and quickly lose their energy. The existence of neutrons was predicted by E. Rutherford 10 years before the experiments of D. Chadwig. On hit α -particles in the nuclei of beryllium, the following reaction occurs:

Here is the symbol of the neutron; its charge is equal to zero, and the relative atomic mass is approximately equal to one. A neutron is an unstable particle: a free neutron in a time of ~ 15 min. decays into a proton, an electron and a neutrino - a particle devoid of rest mass.

After the discovery of the neutron by J. Chadwick in 1932, D. Ivanenko and W. Heisenberg independently proposed proton-neutron (nucleon) model of the nucleus. According to this model, the nucleus consists of protons and neutrons. Number of protons Z coincides with the serial number of the element in the table of D. I. Mendeleev.

Core charge Q determined by the number of protons Z, which are part of the nucleus, and is a multiple of the absolute value of the electron charge e:

Q = + Ze.

Number Z called nuclear charge number or atomic number.

Mass number of the nucleus A called the total number of nucleons, i.e., protons and neutrons contained in it. The number of neutrons in a nucleus is denoted by the letter N. So the mass number is:

A = Z + N.

The nucleons (proton and neutron) are assigned a mass number equal to one, and the electron is assigned a zero value.

The idea of the composition of the nucleus was also facilitated by the discovery isotopes.

Isotopes (from the Greek. isos equal, same and topoa- place) - these are varieties of atoms of the same chemical element, the atomic nuclei of which have the same number of protons ( Z) and a different number of neutrons ( N).

The nuclei of such atoms are also called isotopes. Isotopes are nuclides one element. Nuclide (from lat. nucleus- nucleus) - any atomic nucleus (respectively, an atom) with given numbers Z And N. The general designation of nuclides is ……. Where X- symbol of a chemical element, A=Z+N- mass number.

Isotopes occupy the same place in the Periodic Table of the Elements, hence their name. As a rule, isotopes differ significantly in their nuclear properties (for example, in their ability to enter into nuclear reactions). The chemical (and almost equally physical) properties of isotopes are the same. This is explained by the fact that the chemical properties of an element are determined by the charge of the nucleus, since it is this charge that affects the structure of the electron shell of the atom.

The exception is isotopes of light elements. Isotopes of hydrogen 1 H — protium, 2 H— deuterium, 3 H — tritium they differ so much in mass that their physical and chemical properties are different. Deuterium is stable (i.e., not radioactive) and is included as a small impurity (1: 4500) in ordinary hydrogen. Deuterium combines with oxygen to form heavy water. It boils at normal atmospheric pressure at 101.2°C and freezes at +3.8°C. Tritium β is radioactive with a half-life of about 12 years.

All chemical elements have isotopes. Some elements have only unstable (radioactive) isotopes. For all elements, radioactive isotopes have been artificially obtained.

Isotopes of uranium. The element uranium has two isotopes - with mass numbers 235 and 238. The isotope is only 1/140 of the more common.

Chromatin

1) heterochromatin;

2) euchromatin.

Heterochromatin

Structural

Optional

Euchromatin

a) histone proteins;

b) nonhistone proteins.

Yo Histone proteins (histones

Yo Non-histone proteins

nucleolus

ЁSize - 1-5 microns.

The form is spherical.

Granular component

Fibrillar

nuclear envelope

1. External nuclear membrane (m. nuclearis externa),

inner nuclear membrane

Features:

Karyoplasm

cell reproduction

nuclear apparatus

The nucleus is present in all eukaryotic cells, with the exception of mature erythrocytes and plant sieve tubes. Cells usually have a single nucleus, but sometimes multinucleated cells are found.

The nucleus is spherical or oval.

Some cells have segmented nuclei. The size of the nuclei is from 3 to 10 microns in diameter. The nucleus is essential for the life of the cell. It regulates cell activity. The nucleus stores hereditary information contained in DNA. This information, thanks to the nucleus, is transmitted to daughter cells during cell division. The nucleus determines the specificity of proteins synthesized in the cell. The nucleus contains many proteins necessary for its functions. RNA is synthesized in the nucleus.

cell nucleus comprises membrane, nuclear sap, one or more nucleoli and chromatin.

Functional role nuclear envelope is the isolation of genetic material (chromosome) eukaryotic cell from the cytoplasm with its numerous metabolic reactions, as well as the regulation of bilateral interactions of the nucleus and cytoplasm. The nuclear envelope consists of two membranes - outer and inner, between which is located perinuclear (perinuclear) space. The latter can communicate with the tubules of the cytoplasmic reticulum. outer membrane The nuclear envelope directly contacts with the cytoplasm of the cell, has a number of structural features that allow it to be attributed to the proper ER membrane system. It contains a large number of ribosomes, as well as on the membranes of ergastoplasm. The inner membrane of the nuclear envelope does not have ribosomes on its surface, but is structurally associated with nuclear lamina- fibrous peripheral layer of the nuclear protein matrix.

The nuclear envelope contains nuclear pores with a diameter of 80-90 nm, which are formed due to numerous zones of fusion of two nuclear membranes and are, as it were, rounded, through perforations of the entire nuclear membrane. Pores play an important role in the transport of substances into and out of the cytoplasm. Nuclear pore complex (NPC) with a diameter of about 120 nm has a certain structure (consists of more than 1000 proteins - nucleoporins, whose mass is 30 times greater than the ribosome), which indicates a complex mechanism for the regulation of nuclear-cytoplasmic movements of substances and structures. In the process of nuclear-cytoplasmic transport, nuclear pores function as a kind of molecular sieve, passively passing particles of a certain size along a concentration gradient (ions, carbohydrates, nucleotides, ATP, hormones, proteins up to 60 kDa). Pores are not permanent formations. The number of pores increases during the period of greatest nuclear activity. The number of pores depends on the functional state of the cell. The higher the synthetic activity in the cell, the greater their number. It has been calculated that in lower vertebrates in erythroblasts, where hemoglobin is intensively formed and accumulated, there are about 30 pores per 1 μm2 of the nuclear membrane. In mature erythrocytes of these animals that retain nuclei, up to five pores remain per 1 μg of the membrane, i.e. 6 times less.

In the region of the feather complex, the so-called dense plate - a protein layer that underlies the entire length of the inner membrane of the nuclear membrane. This structure primarily performs a supporting function, since in its presence the shape of the nucleus is preserved even if both membranes of the nuclear envelope are destroyed. It is also assumed that the regular connection with the substance of the dense plate contributes to the ordered arrangement of chromosomes in the interphase nucleus.

Nuclear sap (karyoplasm or matrix)- the internal contents of the nucleus, is a solution of proteins, nucleotides, ions, more viscous than hyaloplasm. It also contains fibrillar proteins. The karyoplasm contains nucleoli and chromatin. Nuclear juice forms the internal environment of the nucleus, and therefore it plays an important role in ensuring the normal functioning of the genetic material. The composition of nuclear juice contains filamentous, or fibrillar, proteins, with which the performance of the support function is associated: the matrix also contains the primary products of transcription of genetic information - heteronuclear RNA (hnRNA), which are processed here, turning into mRNA.

nucleolus- an obligatory component of the nucleus, are found in interphase nuclei and are small bodies, spherical in shape. The nucleoli are denser than the nucleus. In the nucleoli, the synthesis of rRNA, other types of RNA and the formation of subunits takes place. ribosome. The emergence of nucleoli is associated with certain zones of chromosomes called nucleolar organizers. The number of nucleoli is determined by the number of nucleolar organizers. They contain rRNA genes. rRNA genes occupy certain areas (depending on the type of animal) of one or more chromosomes (in humans, 13-15 and 21-22 pairs) - nucleolar organizers, in which the nucleoli are formed. Such regions in metaphase chromosomes look like constrictions and are called secondary constrictions. Using an electron microscope, filamentous and granular components are revealed in the nucleolus. The filamentous (fibrillar) component is represented by complexes of protein and giant RNA precursor molecules, from which smaller molecules of mature rRNA are then formed. In the process of maturation, fibrils are transformed into ribonucleoprotein grains (granules), which represent the granular component.

Chromatin structures in the form of lumps, scattered in the nucleoplasm are an interphase form of existence chromosomes cells.

Ribosome - it is a rounded ribonucleoprotein particle with a diameter of 20-30 nm. Ribosomes are non-membrane cell organelles. Ribosomes combine amino acid residues into polypeptide chains (protein synthesis). Ribosomes are very small and numerous.

It consists of small and large subunits, the combination of which occurs in the presence of messenger (messenger) RNA (mRNA). The small subunit includes protein molecules and one molecule of ribosomal RNA (rRNA), while the second one contains proteins and three rRNA molecules. Protein and rRNA by mass in equal amounts participate in the formation of ribosomes. rRNA is synthesized in the nucleolus.

One mRNA molecule usually combines several ribosomes like a string of beads. Such a structure is called polysome. Polysomes are freely located in the ground substance of the cytoplasm or attached to the membranes of the rough cytoplasmic reticulum. In both cases, they serve as a site for active protein synthesis. Comparison of the ratio of the number of free and membrane-attached polysomes in embryonic undifferentiated and tumor cells, on the one hand, and in specialized cells of an adult organism, on the other hand, led to the conclusion that proteins are formed on hyaloplasmic polysomes for their own needs (for "home" use) of this cell, while on the polysomes of the granular network proteins are synthesized that are removed from the cell and used for the needs of the body (for example, digestive enzymes, breast milk proteins). Ribosomes can be freely located in the cytoplasm or be associated with the endoplasmic reticulum, being part of the rough ER. Proteins formed on ribosomes connected to the ER membrane usually enter the ER tanks. Proteins synthesized on free ribosomes remain in the hyaloplasm. For example, hemoglobin is synthesized on free ribosomes in erythrocytes. Ribosomes are also present in mitochondria, plastids, and prokaryotic cells.

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The structure of the nucleus and its chemical composition

The nucleus consists of chromatin, nucleolus, karyoplasm (nucleoplasm), and nuclear envelope.

In a cell that divides, in most cases there is one nucleus, but there are cells that have two nuclei (20% of liver cells are binuclear), as well as multinuclear (bone tissue osteoclasts).

ЁSizes - range from 3-4 to 40 microns.

Each type of cell is characterized by a constant ratio of the volume of the nucleus to the volume of the cytoplasm. This ratio is called the Hertwing index. Depending on the value of this index, cells are divided into two groups:

1. nuclear - the Hertwing index is of greater importance;

2. cytoplasmic - the Hertwing index has insignificant values.

Yoform - can be spherical, rod-shaped, bean-shaped, annular, segmented.

Yolocalization - the nucleus is always localized in a certain place in the cell. For example, in the cylindrical cells of the stomach, it is in a basal position.

The nucleus in a cell can be in two states:

a) mitotic (during division);

b) interphase (between divisions).

In a living cell, the interphase nucleus looks like an optically empty one; only the nucleolus is found. The structures of the nucleus in the form of threads, grains can be observed only when damaging factors act on the cell, when it goes into a state of paranecrosis (a borderline state between life and death). From this state, the cell can return to normal life or die. After cell death, morphologically, the following changes are distinguished in the nucleus:

1) karyopyknosis - compaction of the nucleus;

2) karyorrhexis - decomposition of the nucleus;

3) karyolysis - dissolution of the nucleus.

Functions: 1) storage and transmission of genetic information,

2) protein biosynthesis, 3) formation of ribosome subunits.

Chromatin

Chromatin (from Greek chroma - color paint) is the main structure of the interphase nucleus, which stains very well with basic dyes and determines the chromatin pattern of the nucleus for each cell type.

Due to the ability to stain well with various dyes, and especially with the main ones, this component of the nucleus was called "chromatin" (Flemming 1880).

Chromatin is a structural analogue of chromosomes and in the interphase nucleus is the carrier DNA of the body.

Morphologically, two types of chromatin are distinguished:

1) heterochromatin;

2) euchromatin.

Heterochromatin(heterochromatinum) corresponds to parts of chromosomes partially condensed in the interphase and is functionally inactive. This chromatin stains very well and it is this chromatin that can be seen on histological preparations.

Heterochromatin, in turn, is divided into:

1) structural; 2) optional.

Structural heterochromatin is the segments of chromosomes that are constantly in a condensed state.

Optional heterochromatin is heterochromatin capable of decondensing and turning into euchromatin.

Euchromatin- these are regions of chromosomes decondensed in interphase. This is a working, functionally active chromatin. This chromatin is not stained and is not detected on histological preparations.

During mitosis, all euchromatin is maximally condensed and becomes part of the chromosomes. During this period, the chromosomes do not perform any synthetic functions. In this regard, cell chromosomes can be in two structural and functional states:

1) active (working), sometimes they are partially or completely decondensed and with their participation in the nucleus, the processes of transcription and reduplication occur;

2) inactive (non-working, metabolic rest), when they are maximally condensed, they perform the function of distribution and transfer of genetic material to daughter cells.

Sometimes, in some cases, the whole chromosome during the interphase can remain in a condensed state, while it looks like smooth heterochromatin. For example, one of the X-chromosomes of the somatic cells of the female body is subject to heterochromatization at the initial stages of embryogenesis (during cleavage) and does not function. This chromatin is called sex chromatin or Barr bodies.

In different cells, sex chromatin has a different appearance:

a) in neutrophilic leukocytes - a type of drumstick;

b) in the epithelial cells of the mucosa - the appearance of a hemispherical lump.

Sex chromatin determination is used to determine the genetic sex, as well as to determine the number of X chromosomes in the karyotype of an individual (it is equal to the number of sex chromatin bodies + 1).

Electron microscopic studies have shown that preparations of isolated interphase chromatin contain elementary chromosomal fibrils 20-25 nm thick, which consist of fibrils 10 nm thick.

Chemically, chromatin fibrils are complex complexes of deoxyribonucleoproteins, which include:

b) special chromosomal proteins;

The quantitative ratio of DNA, protein and RNA is 1:1.3:0.2. The share of DNA in the chromatin preparation is 30-40%. The length of individual linear DNA molecules varies within indirect limits and can reach hundreds of micrometers and even centimeters. The total length of DNA molecules in all chromosomes of one human cell is about 170 cm, which corresponds to 6x10-12g.

Chromatin proteins make up 60-70% of its dry mass and are represented by two groups:

a) histone proteins;

b) nonhistone proteins.

Yo Histone proteins (histones) - alkaline proteins containing basic amino acids (mainly lysine, arginine) are unevenly arranged in blocks along the length of the DNA molecule. One block contains 8 histone molecules that form the nucleosome. The size of the nucleosome is about 10 nm. The nucleosome is formed by compaction and supercoiling of DNA, which leads to a shortening of the length of the chromosome fibril by about 5 times.

Yo Non-histone proteins make up 20% of the number of histones and in the interphase nuclei form a structural network inside the nucleus, which is called the nuclear protein matrix. This matrix represents the framework that determines the morphology and metabolism of the nucleus.

The perichromatin fibrils are 3-5 nm thick, the granules are 45 nm in diameter, and the interchromatin granules are 21-25 nm in diameter.

nucleolus

The nucleolus (nucleolus) is the densest structure of the nucleus, which is clearly visible in a living unstained cell and is a derivative of the chromosome, one of its loci with the highest concentration and active RNA synthesis in the interphase, but is not an independent structure or organelle.

ЁSize - 1-5 microns.

The form is spherical.

The nucleolus has a heterogeneous structure. In a light microscope, its fine-fibrous organization is visible.

Electron microscopy reveals two main components:

a) granular; b) fibrillar.

Granular component represented by granules with a diameter of 15-20 nm, these are maturing subunits of ribosomes. Sometimes the granular component forms filamentous structures - nucleolonemes, about 0.2 µm thick. The granular component is localized along the periphery.

Fibrillar the component is ribonucleoprotein strands of ribosome precursors, which are concentrated in the central part of the nucleolus.

The ultrastructure of the nucleoli depends on the activity of RNA synthesis: at a high level of synthesis, a large number of granules are detected in the nucleolus, when synthesis is stopped, the number of granules decreases and the nucleoli turn into dense fibrillar strands of a basophilic nature.

nuclear envelope

The nuclear envelope (nuclolemma) consists of:

Physics of the atomic nucleus. Core composition.

The outer nuclear membrane (m. nuclearis externa),

2. The inner membrane (m. nuclearis interna), which are separated by the perinuclear space or the cistern nuclear envelope (cisterna nucleolemmae), 20-60 nm wide.

Each membrane has a thickness of 7-8nm. In general, the nuclear membrane resembles a hollow two-layer bag that separates the contents of the nucleus from the cytoplasm.

Outer membrane of the nuclear envelope, which is in direct contact with the cytoplasm of the cell, has a number of structural features that allow it to be attributed to the proper membrane system of the endoplasmic reticulum. These features include: the presence of numerous polyribosomes on it from the side of the hyaloplasm, and the outer nuclear membrane itself can directly pass into the membranes of the granular endoplasmic reticulum. The surface of the outer nuclear membrane in most animal and plant cells is not smooth and forms outgrowths of various sizes towards the cytoplasm in the form of vesicles or long tubular formations.

inner nuclear membrane associated with the chromosomal material of the nucleus. From the side of the karyoplasm, the so-called fibrillar layer, consisting of fibrils, is adjacent to the inner nuclear membrane, but it is not characteristic of all cells.

The nuclear envelope is not continuous. The most characteristic structures of the nuclear envelope are nuclear pores. Nuclear pores are formed by the fusion of two nuclear membranes. In this case, rounded through holes (perforations, annulus pori) are formed, which have a diameter of about 80-90 nm. These holes in the nuclear membrane are filled with complex globular and fibrillar structures. The combination of membrane perforations and these structures is called the pore complex (complexus pori). The pore complex consists of three rows of granules, eight in each row, the diameter of the granules is 25 nm; fibrillar processes extend from these granules. Granules are located on the border of the hole in the nuclear envelope: one row lies on the side of the nucleus, the second - on the side of the cytoplasm, the third in the central part of the pore. Fibrils extending from peripheral granules can converge in the center and create, as it were, a partition, a diaphragm across the pore (diaphragma pori). The pore sizes of this cell are usually stable. The number of nuclear pores depends on the metabolic activity of the cells: the more intense the synthetic processes in the cell, the more pores per unit surface of the cell nucleus.

Features:

1. Barrier - separates the contents of the nucleus from the cytoplasm, limits the free transport of macromolecules between the nucleus and the cytoplasm.

2. Creation of intranuclear order - fixation of chromosomal material in the three-dimensional lumen of the nucleus.

Karyoplasm

Karyoplasm is the liquid part of the nucleus, in which nuclear structures are located, it is an analogue of hyaloplasm in the cytoplasmic part of the cell.

cell reproduction

One of the most important biological phenomena, which reflects general patterns and is an essential condition for the existence of biological systems for a sufficiently long period of time, is the reproduction (reproduction) of their cellular composition. Reproduction of cells, according to cell theory, is carried out by dividing the original. This position is one of the main ones in the cell theory.

The nucleus (nucleus) of the cell

CORE FUNCTIONS

Chromatin -

Chromosomes

which include:

- histone proteins

– small amounts of RNA;

nuclear matrix

Consists of 3 components:

laying the nuclear envelope.

What is a nucleus - is it in biology: properties and functions

Intranuclear network (skeleton).

3. "Residual" nucleolus.

It consists of:

- outer nuclear membrane;

Nucleoplasm (karyoplasm)- the liquid component of the nucleus, in which chromatin and nucleoli are located. Contains water and a number

nucleolus

The nucleus (nucleus) of the cell- system of genetic determination and regulation of protein synthesis.

CORE FUNCTIONS

● storage and maintenance of hereditary information

● implementation of hereditary information

The nucleus consists of chromatin, nucleolus, karyoplasm (nucleoplasm) and a nuclear envelope that separates it from the cytoplasm.

Chromatin - these are zones of dense matter in the nucleus, which

Rosho perceives different dyes, especially basic ones.

In non-dividing cells, chromatin is found in the form of lumps and granules, which is an interphase form of the existence of chromosomes.

Chromosomes- chromatin fibrils, which are complex complexes of deoxyribonucleoproteins (DNP), in the composition

which include:

- histone proteins

- non-histone proteins - make up 20%, these are enzymes, perform structural and regulatory functions;

– small amounts of RNA;

- small amounts of lipids, polysaccharides, metal ions.

nuclear matrix– is a framework intranuclear system

mine, the unifying backbone for chromatin, nucleolus, nuclear envelope. This structural network is the basis that determines the morphology and metabolism of the nucleus.

Consists of 3 components:

1. Lamina (A, B, C) - peripheral fibrillar layer, sub-

laying the nuclear envelope.

2. Intranuclear network (skeleton).

3. "Residual" nucleolus.

Nuclear envelope (karyolemma) is a membrane that separates the contents of the nucleus from the cytoplasm of the cell.

It consists of:

- outer nuclear membrane;

- the inner nuclear membrane, between which is the perinuclear space;

- the double-membrane nuclear envelope has a pore complex.

Nucleoplasm (karyoplasm)- the liquid component of the nucleus, in which chromatin and nucleoli are located.

Core. Kernel Components

Contains water and a number

substances dissolved and suspended in it: RNA, glycoproteins,

ions, enzymes, metabolites.

nucleolus- the densest structure of the nucleus, formed by specialized areas - loops of chromosomes, which are called nucleolar organizers.

There are 3 components of the nucleolus:

1. The fibrillar component is the primary rRNA transcripts.

2. The granular component is an accumulation of pre-

ribosome subunits.

3. Amorphous component - areas of the nucleolar organizer,

studopedia.org - Studopedia.Org - 2014-2018. (0.001 s) ...

The nucleus is the main regulatory component of the cell. Its structure and functions.

The nucleus is an essential part of eukaryotic cells. This is the main regulatory component of the cell. It is responsible for the storage and transmission of hereditary information, controls all metabolic processes in the cell. . Not an organoid, but a component of a cell.

The core consists of:

1) the nuclear envelope (nuclear membrane), through the pores of which the exchange between the cell nucleus and the cytoplasm takes place.

2) nuclear juice, or karyoplasm, is a semi-liquid, weakly stained plasma mass that fills all the nuclei of the cell and contains the remaining components of the nucleus;

3) chromosomes that are visible in the non-dividing nucleus only with the help of special microscopy methods. The set of chromosomes in a cell is called aryotype. Chromatin on stained cell preparations is a network of thin strands (fibrils), small granules or clumps.

4) one or more spherical bodies - nucleoli, which are a specialized part of the cell nucleus and are associated with the synthesis of ribonucleic acid and proteins.

two kernel states:

1. interphase nucleus - has nuclei. sheath - karyolemma.

2. nucleus during cell divisions. only chromatin is present in a different state.

The nucleolus includes two zones:

1. inner-fibrillar-protein molecules and pre-RNA

2. outer - granular - form subunits of ribosomes.

The nuclear envelope consists of two membranes separated by a perinuclear space. Both of them are permeated with numerous pores, thanks to which the exchange of substances between the nucleus and the cytoplasm is possible.

The main components of the nucleus are chromosomes, formed from a DNA molecule and various proteins. In a light microscope, they are clearly distinguishable only during the period of cell division (mitosis, meiosis). In a non-dividing cell, the chromosomes look like long thin threads distributed throughout the entire volume of the nucleus.

The main functions of the cell nucleus are as follows:

data storage;
transfer of information to the cytoplasm using transcription, i.e., the synthesis of information-carrying i-RNA;
transfer of information to daughter cells during replication - division of cells and nuclei.
regulates biochemical, physiological and morphological processes in the cell.

takes place in the nucleus replication- duplication of DNA molecules, as well as transcription- synthesis of RNA molecules on a DNA template. In the nucleus, the synthesized RNA molecules undergo some modifications (for example, during splicing insignificant, meaningless regions are excluded from messenger RNA molecules), after which they enter the cytoplasm . Ribosome assembly also occurs in the nucleus, in special formations called nucleoli. The compartment for the nucleus - the karyotheca - is formed by expanding and merging with each other the tanks of the endoplasmic reticulum in such a way that the nucleus has double walls due to the narrow compartments of the nuclear membrane surrounding it. The cavity of the nuclear envelope is called lumen or perinuclear space. The inner surface of the nuclear envelope is underlain by the nuclear lamina- a rigid protein structure formed by lamins proteins, to which strands of chromosomal DNA are attached. In some places, the inner and outer membranes of the nuclear envelope merge and form the so-called nuclear pores through which material exchange occurs between the nucleus and the cytoplasm.

12. Two-membrane organelles (mitochondria, plastids). Their structure and functions.

Mitochondria - these are rounded or rod-shaped structures, often branching, 0.5 µm thick and usually up to 5-10 µm long.

The shell of mitochondria consists of two membranes that differ in chemical composition, a set of enzymes, and functions. Inner membrane forms invaginations of leaf-like (cristae) or tubular (tubules) shape. The space bounded by the inner membrane is matrix organelles. Using an electron microscope, grains with a diameter of 20-40 nm are detected in it. They accumulate calcium and magnesium ions, as well as polysaccharides, such as glycogen.
The matrix contains its own organelle protein biosynthesis apparatus. It is represented by 2-6 copies of a circular and histone-free (as in prokaryotes) DNA molecule, ribosomes, a set of transport RNA (tRNA), enzymes for DNA replication, transcription and translation of hereditary information. Main function mitochondria consists in the enzymatic extraction of energy from certain chemicals (by their oxidation) and the accumulation of energy in a biologically usable form (by the synthesis of adenosine triphosphate -ATP molecules). In general, this process is called oxidative phosphorylation. Among the side functions of mitochondria, one can name participation in the synthesis of steroid hormones and some amino acids (glutamine).

plastids - these are semi-autonomous (they can exist relatively autonomously from the nuclear DNA of the cell) two-membrane organelles characteristic of photosynthetic eukaryotic organisms. There are three main types of plastids: chloroplasts, chromoplasts and leukoplasts.The totality of plastids in a cell is calledplastidoma . Each of these types, under certain conditions, can pass one into another. Like mitochondria, plastids contain their own DNA molecules. Therefore, they are also able to reproduce independently of cell division. Plastids are found only in plant cells.

Chloroplasts. The length of chloroplasts ranges from 5 to 10 microns, the diameter is from 2 to 4 microns. Chloroplasts are bounded by two membranes. The outer membrane is smooth, the inner one has a complex folded structure. The smallest fold is called t ilakoid. A group of thylakoids stacked like a stack of coins is called a g wound. The granules are connected to each other by flattened channels - lamellae. The thylakoid membranes contain photosynthetic pigments and enzymes that provide ATP synthesis. The main photosynthetic pigment is chlorophyll, which determines the green color of chloroplasts.

The inner space of chloroplasts is filled stroma. The stroma contains circular naked DNA, ribosomes, enzymes of the Calvin cycle, and starch grains. Inside each thylakoid there is a proton reservoir, there is an accumulation of H +. Chloroplasts, like mitochondria, are capable of autonomous reproduction by dividing in two. The chloroplasts of lower plants are called chromatophores.

Leucoplasts. The outer membrane is smooth, the inner one forms small thylakoids. The stroma contains circular "naked" DNA, ribosomes, enzymes for the synthesis and hydrolysis of reserve nutrients. There are no pigments. Especially many leukoplasts have cells of the underground organs of the plant (roots, tubers, rhizomes, etc.). .). Amyloplasts- synthesize and store starch , elaioplast- oils , proteinoplasts- proteins. Different substances can accumulate in the same leukoplast.

Chromoplasts. The outer membrane is smooth, the inner or also smooth, or forms single thylakoids. The stroma contains circular DNA and pigments. - carotenoids, giving chromoplasts a yellow, red, or orange color. The form of accumulation of pigments is different: in the form of crystals, dissolved in lipid drops, etc. Chromoplasts are considered the final stage in the development of plastids.

Plastids can mutually transform into each other: leukoplasts - chloroplasts - chromoplasts.

Single-membrane organelles (ER, Golgi apparatus, lysosomes). Their structure and functions.

tubular And vacuolar system formed by communicating or separate tubular or flattened (cistern) cavities, limited by membranes and spreading throughout the cytoplasm of the cell. In this system, there are rough And smooth cytoplasmic reticulum. A feature of the structure of the rough network is the attachment of polysomes to its membranes. Because of this, it performs the function of synthesizing a certain category of proteins that are mainly removed from the cell, for example, secreted by gland cells. In the area of the rough network, the formation of proteins and lipids of cytoplasmic membranes, as well as their assembly. Densely packed into a layered structure, cisterns of a rough network are the sites of the most active protein synthesis and are called ergastoplasm.

The membranes of the smooth cytoplasmic reticulum are devoid of polysomes. Functionally, this network is associated with the metabolism of carbohydrates, fats and other non-protein substances, such as steroid hormones (in the gonads, adrenal cortex). Through the tubules and cisterns, substances move, in particular, the material secreted by the glandular cell, from the site of synthesis to the packing area into granules. In areas of liver cells rich in smooth network structures, harmful toxic substances and some drugs (barbiturates) are destroyed and rendered harmless. In the vesicles and tubules of the smooth network of striated muscles, calcium ions are stored (deposited), which play an important role in the contraction process.

Golgi complex-is a stack of flat membrane sacs called cisterns. The tanks are completely isolated from each other and are not interconnected. Numerous tubules and vesicles branch off from the cisterns along the edges. Vacuoles (vesicles) with synthesized substances are laced from the EPS from time to time, which move to the Golgi complex and connect with it. Substances synthesized in the EPS become more complex and accumulate in the Golgi complex. Functions of the Golgi complex :1- In the tanks of the Golgi complex, there is a further chemical transformation and complication of substances that have entered it from the EPS. For example, substances are formed that are necessary to renew the cell membrane (glycoproteins, glycolipids), polysaccharides.

2- In the Golgi complex there is an accumulation of substances and their temporary "storage"

3- Formed substances are “packed” into vesicles (in vacuoles) and in this form move through the cell.

4- In the Golgi complex, lysosomes are formed (spherical organelles with degrading enzymes).

Lysosomes- small spherical organelles, the walls of which are formed by a single membrane; contain lytic(cleaving) enzymes. At first, the lysosomes, laced from the Golgi complex, contain inactive enzymes. Under certain conditions, their enzymes are activated. When a lysosome fuses with a phagocytic or pinocytic vacuole, a digestive vacuole is formed, in which various substances are digested intracellularly.

Functions of lysosomes :1- Carry out the splitting of substances absorbed as a result of phagocytosis and pinocytosis. Biopolymers are broken down into monomers that enter the cell and are used for its needs.

The nucleus and its structural components

For example, they can be used to synthesize new organic substances, or they can be further broken down for energy.

2- Destroy old, damaged, excess organelles. Splitting of organelles can also occur during starvation of the cell.

Vacuoles- spherical single-membrane organelles, which are reservoirs of water and substances dissolved in it. Vacuoles include: phagocytic and pinocytic vacuoles, digestive vacuoles, vesicles, laced from the EPS and the Golgi complex. Animal cell vacuoles are small and numerous, but their volume does not exceed 5% of the total cell volume. Their main function - transport of substances through the cell, the implementation of the relationship between organelles.

In a plant cell, vacuoles account for up to 90% of the volume.

In a mature plant cell, there is only one vacuole, it occupies a central position. The vacuole membrane of a plant cell is the tonoplast, its contents are cell sap. Functions of vacuoles in a plant cell: maintaining the cell membrane in tension, accumulation of various substances, including waste products of the cell. Vacuoles supply water for photosynthesis. May include:

- reserve substances that can be used by the cell itself (organic acids, amino acids, sugars, proteins). - substances that are excreted from the metabolism of the cell and accumulate in the vacuole (phenols, tannins, alkaloids, etc.) - phytohormones, phytoncides,

- pigments (coloring substances) that give the cell sap a purple, red, blue, violet color, and sometimes yellow or cream. It is the pigments of cell sap that color flower petals, fruits, root crops.

14. Non-membrane organelles (microtubules, cell center, ribosomes). Their structure and functions.Ribosome - a non-membrane organelle of the cell that performs protein synthesis. Consists of two subunits - small and large. The ribosome consists of 3-4 rRNA molecules that form its framework, and several dozen molecules of various proteins. Ribosomes are synthesized in the nucleolus. In a cell, ribosomes can be located on the surface of the granular ER or in the hyaloplasm of the cell in the form of polysomes. Polysome - it is a complex of i-RNA and several ribosomes that read information from it. Function ribosome- protein biosynthesis. If ribosomes are located on the ER, then the proteins synthesized by them are used for the needs of the whole organism, hyaloplasmic ribosomes synthesize proteins for the needs of the cell itself. The ribosomes of prokaryotic cells are smaller than those of eukaryotes. The same small ribosomes are found in mitochondria and plastids.

microtubules - hollow cylindrical structures of the cell, consisting of the irreducible protein tubulin. Microtubules are incapable of contraction. The walls of the microtubule are formed by 13 strands of the protein tubulin. Microtubules are located in the thickness of the hyaloplasm of cells.

Cilia and flagella - organelles of movement. Main function - movement of cells or movement along the cells of the fluid or particles surrounding them. In a multicellular organism, cilia are characteristic of the epithelium of the respiratory tract, fallopian tubes, and flagella are characteristic of spermatozoa. Cilia and flagella differ only in size - the flagella are longer. They are based on microtubules arranged in a 9(2) + 2 system. This means that 9 double microtubules (doublets) form a cylinder wall, in the center of which there are 2 single microtubules. The cilia and flagella are supported by the basal bodies. The basal body has a cylindrical shape, formed by 9 triplets (triplets) of microtubules; there are no microtubules in the center of the basal body.

cl e exact center — mitotic center, a permanent structure in almost all animal and some plant cells, determines the poles of a dividing cell (see Mitosis) . The cell center usually consists of two centrioles - dense granules 0.2-0.8 in size micron, located at right angles to each other. During the formation of the mitotic apparatus, centrioles diverge towards the poles of the cell, determining the orientation of the spindle of cell division. Therefore, it is more correct to K. c. call mitotic center, reflecting by this its functional significance, especially since only in some cells K. c. located in its center. In the course of development of the organism, they change as the position of K. c. in cells, so is the shape of it. When a cell divides, each of the daughter cells receives a pair of centrioles. The process of their duplication occurs more often at the end of the previous cell division. Emergence of a number of pathological forms of cell division is connected with abnormal division To. c.