The most traditional substrates for respiration in plants are. Breathing substrates

Despite the fact that premenstrual syndrome is just a complex of symptoms, with an unclear pathogenesis, its treatment methods are quite extensive and varied.

They include the effects of both pathogenetic and symptomatic means, methods of psychotherapy and homeopathy, hormonal therapy and treatment with oral contraceptives.

Such a variety of treatment methods is based on the peculiarities of the clinical manifestations of premenstrual tension syndrome in individual patients. Every woman suffering from PMS has an individual clinical picture, and treatment should be aimed precisely at eliminating specific manifestations that are characteristic of the patient's body.

In this article, we only consider modern approach to the treatment of premenstrual syndrome. Causes, pathogenesis and classification of clinical forms of PMS.

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1. Basic methods of treatment

Modern methods of therapy are able to correct due to a wide selection of groups of drugs.

1 Non-drug therapy (diet, psychotherapy, lifestyle correction, physical activity, taking vitamins, and other methods).
2 Pathogenetic therapy includes the following groups of drugs for PMS:
- GnRH agonists;
- antigonadotropic drugs;
- antiestrogens;
- monophasic combined oral contraceptives;
- gestagens;
- estrogens.
3 Symptomatic therapy is provided by the following groups of drugs:
- psychotropic medicines(anxiolytics, antidepressants);
- non-steroidal anti-inflammatory drugs (NSAIDs);
- diuretics;
- dopaminomimetics;
- herbal and homeopathic medicines;
- adaptogens.

2. Non-drug correction

Its integral part is psychotherapy, aimed at the patient's acceptance of herself and the cyclical changes that occur to her, strengthening self-control.

This is especially true for women with psychovegetative and crisis forms of the syndrome. Their mastery of the situation, their own emotions directly depends on the severity of the symptoms, therefore, it is likely that the patient will completely overcome panic attacks and crises.

In this case, compliance with the daily regimen, good sleep and rest are extremely important. An important aspect is the inclusion of physical activity in the daily routine - charging in the morning and evening for 30 minutes in the fresh air.

Another type of non-drug therapy is diet. It is necessary to exclude or significantly reduce the amount of consumed carbohydrates and sugar, coffee and alcohol, salt, tea, animal fats, milk, especially paying attention to this during the second half of the menstrual cycle.

It is advisable to introduce more fruits and vegetables into the diet. Physiotherapy has a positive effect, especially electrosleep and massage (general, cervical-collar region).

Non-drug correction is not ideal and is not able to fully exclude the occurrence of premenstrual tension syndrome, although it finds a response abroad.

The difference in the mentality of women in Russia and, for example, Europe, plays a role here. As you know, European women are sensitive to their mental health, therefore, they are fully fulfilling such recommendations.

Unfortunately, Russian women do not take this approach seriously. The overwhelming majority of patients have no desire to radically change their lifestyle, because this requires a lot of effort.

3. Vitamins for PMS

For the normal functioning of the reproductive and endocrine systems, a woman needs a sufficient intake of fat-soluble vitamins (Aevit, 1 capsule once a day, or taking multivitamins, or correction of the diet). It is necessary to consider in more detail such an important trace element as magnesium.

A lot of works have been written about its positive effect on the course of the cyclic syndrome, a sufficient number of studies have been carried out so that drugs based on it are widely used in the practice of a gynecologist. True, all existing studies were carried out in Russia, which somewhat diminishes the optimism of a sane person.

It should be borne in mind that we are talking about organic salts of this substance, such as citrate, lactate, orotate, pidolate. Inorganic salts (magnesium sulfate) are used in obstetric and gynecological practice for the treatment of preeclampsia and eclampsia, correction of blood pressure.

The greatest digestibility is possessed by magnesium citrate in combination with vitamin B6. These requirements are fully met by the drug "Magne B6 Forte" manufactured by Sanofi (France).

Picture 1 - Magne B6 forte (magnesium citrate + pyridoxine hydrochloride)

4. Pathogenetic agents

Pathogenetic therapy is the most serious in premenstrual syndrome. Prescribing the following drugs for PMS requires mandatory observation by a gynecologist!

4.1. GnRH agonists and antigonadotropic drugs

GnRH agonists and antigonadotropic drugs are used exclusively for severe menstrual tension syndrome, or when another type of therapy is impossible.

Their use is limited by significant side effects, such as the development of osteoporosis, the shutdown of ovarian function, although they give definitely visible results when they are used.

If the use of this group of drugs is inevitable, the so-called "return" therapy with estrogens is possible.

Treatment regimens can be as follows:

1 Buserelin 150 mg as a nasal spray from the second day of the cycle, duration of treatment is 6 months;
2 Goserelin in solution 0.36 g subcutaneously once every 28 days, the duration of therapy is 6 months;
3 Leiprorelin in solution 0.375 g once every 28 days for 6 months;
4 Triptorelin intramuscularly 0.375 g once every 28 days.

4.2. Antiestrogens

Antiestrogens in this case are similar in their action to the previous group of drugs. The drug tamoxifen is used orally at 0.1 g once a day.

4.3. Monophasic COCs

Monophasic combined oral contraceptives are the most popular and modern method treatment of premenstrual syndrome both in Russia and abroad.

The negative impact on the body of this group of drugs is minimized, they are regularly improved, which expands the possibility of using oral contraceptives among the female population.

The use of this group of drugs is pathogenetically justified, since oral contraceptives should stabilize the ratio of estrogens / gestagens, the imbalance of which is most often observed at the basis of premenstrual syndrome.

However, the previously used classical gestagens (such as levonorgestrel, norgestimate, norethisterone) not only did not suppress the symptoms, but sometimes exacerbated them, increasing aggressiveness, irritability, and contributed to an increase in body weight, which was associated with their lack of antimineralcorticoid activity.

Currently, an innovative gestagen - drospirenone, which has been introduced into clinical practice not so long ago, is actively used and shows excellent results, which has a pronounced antimineralocorticoid activity. Due to this, drospirenone eliminates, first of all, symptoms such as puffiness, mastodynia, mastalgia.

Drospirenone is a synthetic substance derived from spironolactone, which provides it with pronounced antimineralocorticoid and antiandrogenic activity.

Figure 2 - Angelique (Drospirenonum + Oestradiolum (genus Drospirenoni + Oestradioli)

Its use eliminates all estrogen-dependent manifestations of premenstrual tension syndrome by blocking androgen receptors.

Consequently, when using it, there is no increase in body weight, nervousness, irritability, aggressiveness, mood swings, headaches, edema, acne and seborrhea disappear.

The following schemes for the use of monophasic oral contraceptives (tablets for PMS) are also possible:

1 Ethinylestradiol / gestodene orally 0.3 mg / 0.75 mg once a day at one pre-selected time from the first to the 21st days of the cycle with a skip for 7 days;
2 Ethinylestradiol / desogestrel orally 0.3 mg / 0.15 mg once a day at one preselected time from the first to the 21st days of the cycle with a skip for 7 days;
3 Ethinylestradiol / dienogest orally 0.3 mg / 2 mg once a day at one preselected time from the first to the 21st days of the monthly cycle with a skip for 7 days;
4 Ethinylestradiol / cyproterone inside 0.35 mg / 2 mg once a day at the same pre-selected time from the first to the 21st days of the cycle with a skip for 7 days;
5 Ethinylestradiol / drospirenone orally in the form of tablets 0.3 mg / 3 mg once a day at one pre-selected time from the first to the 21st days of the cycle with a skip for 7 days.

For all of these combinations, the generally accepted duration of therapy is from 3 months to six months, followed by monitoring of the effectiveness.

4.4. Gestagens

Gestagens are used with insufficient function of the corpus luteum, especially with its severe course, a combination of premenstrual tension syndrome and endometrial hyperplastic processes.

As mentioned above, the use of exclusively gestagens is currently significantly reduced due to the creation of new drugs with a more pronounced positive activity for relieving PMS symptoms.

The treatment regimens with gestagens are as follows:

1 Dydrogesterone 20 mg from the 16th day of the monthly cycle for 10 days; - medroxyprogesterone acetate 150 mg intramuscularly every 9 days;
2 Levonorgestrel, an intrauterine system, is injected into the uterine cavity on the 4-6th day of the monthly cycle once.

The intrauterine system is a T-shaped rod with a special storage device that contains 52 mg of levonorgestrel. The storage unit with the hormone is covered with a special membrane that controls the flow of levonorgestrel into the uterine cavity and maintains it at a level of 20 μg.

Figure 3 - Mirena - intrauterine system (Levonorgestrel * (Levonorgoestrelum))

The next, and often the only possible stage in the treatment of premenstrual syndrome is symptomatic. In this case, only the symptoms that disturb the patient's life are veiled with the help of not only medicinal, but also homeopathic, herbal remedies.

5. Symptomatic treatment

Psychotropic drugs such as anxiolytics, antidepressants, antipsychotics require serious justification for their appointment. In this case, these drugs are prescribed jointly by a gynecologist and a neurologist, or a psychiatrist / psychotherapist, in order to exclude all possible side effects typical for this group of drugs.

5.1. Anxiolytics and antipsychotics

Anxiolytics (or anti-anxiety drugs) are prescribed for neuropsychiatric disorders of varying severity.

They are effective for such manifestations of premenstrual tension syndrome as anxiety, irritability, anxiety, aggression, mood lability.

For the monotherapy of depression or depression with increased anxiety, this group of drugs is not preferred.

The standard treatment regimens for anxiolytics are as follows:

1 Alprazolam 0.1 g, duration of therapy 3 months;
2 Diazepam orally 5-15 mg per day up to 3 times a day;
3 Clonazepam inside 0.5 mg once a day;
4 Mebikar inside, 0.3-0.6 mg 3 times a day;
5 Medazepam 10 mg orally once a day.

Of the antipsychotics, the drug thioridazine is used orally at 10-25 mg.

5.2. Antidepressants

Antidepressants have firmly taken their place in life. modern man and at the moment are used not only for the correction of mental disorders, but also in the treatment psychosomatic diseases, with neuropsychic manifestations, which can include a cyclic illness.

Especially treatment with antidepressants, like oral contraceptives, is popular in Europe and the USA. The population of these countries has long discovered positive influence drugs of these groups and is not as wary of them as, say, residents of Russia.

For the treatment of premenstrual syndrome from antidepressants, selective serotonin reuptake inhibitors (sertraline, paroxetine, fluvoxamine, fluoxetine) are used.

This group of drugs has a rather mild thymoanaleptic effect, relieves anxiety, tension, improves the general psycho-emotional background and is characterized by good tolerance.

But when prescribing them, the characteristics of each drug should also be taken into account. Despite the fact that they belong to the same group, for fluoxetine and sertraline the so-called stimulating "secondary" effect is more characteristic, while for paroxetine and fluvoskamine, on the contrary, sedative.

Also, the correct selection of the dose and treatment regimen plays a very important role. Start therapy with 1/4 of the dose in the morning (for drugs with a stimulating effect) or in the evening (for drugs with a sedative effect).

After 7 days, the dose is increased to ½ and so on up to 1-2 tablets, until the patient notes the expected effect.

Usually, 1 tablet per day becomes a sufficient dose, given that some cyclicality must be observed: as a rule, a decrease in the dose of the drug in the first half of the cycle and its gradual increase by the time of the greatest manifestation of premenstrual syndrome.

The positive effect of treatment with this group of drugs should be expected in 60-90 days, the duration of therapy is 6-9 months, but if indicated, it can be extended up to 12 months.

Standard antidepressant regimens:

1 Sertraline inside 0.50 g once a day;
2 Tianeptine orally 0.125 g;
3 Fluoxetine 20-40 mg orally in the morning;
4 Citalopram 10–20 mg orally in the morning.

5.3. Non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs in the form of tablets are prescribed mainly for the cephalgic form of PMS.

Here, an important role is played by the antiprostaglandin effect inherent in this group of drugs, since the role of prostaglandins in the pathogenesis of premenstrual tension syndrome is known. Apply:

1 Ibuprofen inside 0.2-0.4 g;
2 Indomethacin 25-50 mg;
3 Naproxen by mouth 250 mg.

5.4. Diuretics

Diuretics - aldosterone antagonists are used, which have potassium-sparing, hypotensive and diuretic effects. Diuretics are indicated for edematous manifestations of premenstrual syndrome.

Spironolactone (Veroshpiron) is used at a dose of 25 mg 3-4 days before the onset of the expected symptoms. The course of treatment is 1 month.

5.5. Dopaminomimetics

Dopaminomimetics are used when an increase in prolactin is detected. The drugs in this group were among the first to be used to treat the symptoms of premenstrual syndrome.

They, first of all, eliminate symptoms such as mastodynia and mastalgia.

Common drugs and treatment regimens are as follows:

1 Bromocriptine inside 1.25-2.5 mg for 3 months;
2 Cabergoline 0.25-0.5 mg 2 times a week;
3 Quinagolide 75-150 mg.

It should be remembered that this group of drugs is prescribed from the 14th to the 16th day of the monthly cycle, when the highest concentrations of prolactin are observed.

5.6. Herbal remedies and homeopathy

Herbal and homeopathic remedies are quite popular in Russia and are widely used to relieve some of the symptoms of premenstrual syndrome.

A lot of studies have been carried out on the effect of such biologically active additives on the body as a whole and on the elimination of the necessary symptoms in particular.

Each doctor has his own opinion and attitude towards this group of drugs, but sometimes, with intolerance to synthetic drugs, it is the substances of this group that come to the rescue.

For example, the drug Cyclodinone is used as an alternative to bromocriptine. There are studies of this drug, which even testify to its effectiveness in severe and moderate manifestations of the cyclic syndrome, have a dopaminergic effect and reduce the level of prolactin. Mastodinon has a similar effect.

5.7. Adaptogens

They are also biologically active substances that increase the body's ability to resist unfavorable factors of the external and internal environment and provide homeostasis in changing environmental conditions.

The purpose of using this group of drugs is to create increased body resistance. They are more effective in complex therapy, and not as the only possible means.

Since this group, akin to homeopathic remedies, does not always find a response from doctors, it is rarely prescribed, and often patients begin to take them on their own.

When using adaptogens, strict adherence to daily biorhythms is necessary, since they have the ability to increase the level of catecholamines in the blood.

It is preferable to use them in the morning. The expected effect when taking adaptogens is achieved only with prolonged systematic use (at least 6 months).

By origin, adaptogens are divided into several groups:

1 Vegetable origin (ginseng, eleutherococcus, schisandra chinensis, Manchurian aralia, zamaniha, etc.);
2 Mineral resources of plant origin (humic substances);
3 Analogs of natural human hormones (melatonin);
4 Synthetic (ethylthiobenzimidazole hydrobromide monohydrate).

5.8. How to evaluate the effectiveness of treatment?

For more successful treatment, it is necessary for a woman to keep a diary, where she should note the severity of symptoms in points:

1 0 points - no symptoms;
2 1 point - weak disturbance;
3 2 points - disturbed in an average degree, but did not change the quality of life;
4 3 points - severe symptoms that disrupt the woman's quality of life.

It is in this case that for working together the woman herself and her attending physician will achieve the most effective results.

There is also evidence of a surgical method for treating cyclic syndrome - oophorectomy in severe forms that do not respond to conservative treatment. Also, such an operation may be quite appropriate in women after 35 years of age with realized reproductive function.

This will provide not only the effect of eliminating the symptoms of premenstrual syndrome, but also a reliable contraceptive. The lack of estrogen in this case is corrected by the appointment of hormone replacement therapy.

Plants use carbohydrates as the main substrate for respiration, and free sugars are oxidized first. With their lack, polysaccharides, proteins, fats after their hydrolysis can be used. Poly- and disaccharides are hydrolyzed to monosaccharides, proteins - to amino acids, fats - to glycerol and fatty acids.

The use of fats begins with their hydrolytic breakdown by lipacha to glycerol and fatty acids, which occurs in spherosomes. Due to phosphorylation and subsequent oxidation, glycerol is converted into phosphotriose - PHA, which is included in the main pathway of carbohydrate metabolism.

Fatty acids are oxidized by the β-oxidation mechanism, as a result of which bicarbon acetyl residues are sequentially cleaved from the fatty acid in the form of acetyl-CoA. This process takes place in glyoxisomes, where, in addition, enzymes of the glyoxylate cycle are localized. Acetyl-CoA is involved in the reactions of the glyoxylate cycle, the end product of which, succinate, leaves the glyoxisome and participates in the Krebs cycle in mitochondria (Fig.). The malate synthesized in the TCA in the cytoplasm with the participation of malate dehydrogenase is converted into oxaloacetate, which, with the help of PEP carboxylase, gives PEP. PHA and PEP serve as the starting material for the synthesis of glucose (as well as fructose and sucrose) in reverse glycolysis reactions. The process of glucose formation from non-carbohydrate precursors is called gluconeogenesis. ... It has been experimentally proven that as seeds germinate, the fat content decreases and the sugar content increases.

Storage proteins are used for respiration as a result of hydrolysis to amino acids and subsequent oxidation to acetyl-CoA or keto acids, which then enter the Krebs cycle (Fig.)

Complete oxidation The considered substrates are carried out to carbon dioxide and water with the release of the energy of oxidizable substances.

The ratio of the number of moles of CO 2 released during respiration to the number of moles of absorbed O 2 is called the respiratory coefficient (DC). For hexoses, he is equal to one:/

C 6 O 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O; DC = 6CO 2 / 6O 2 = 1

The amount of oxygen required for the oxidation of the substrate is in inverse relationship from its content in the substrate molecule. Therefore, if the substrate for respiration is fatty acids poorer in oxygen (in comparison with carbohydrates), then the DC will be less spruce:

C 18 H 36 O 2 + 26O 2 → 18CO 2 + 18H 2 O; DC = 18 CO 2/26 O 2 = 0.69

Other factors also affect the value of DC, for example, lack of oxygen (when the roots are flooded, etc.), fermentation intensifies and DC increases; if, as a result of undeoxidation of products, organic acids accumulate in the tissues, and the amount of carbon dioxide decreases, the DC falls.

Rice. Use of polysaccharides, proteins and fats as respiratory substrates.

Respiration dependence on environmental factors

1. Oxygen concentration

The breathing process is associated with continuous oxygen consumption. But oxidative transformations of substrates include aerobic and anaerobic processes (glycolysis, fermentation). A decrease in the partial pressure of oxygen from 21% to 5%, the intensity of tissue respiration changes insignificantly.

For the first time, the influence of oxygen on the amount of consumption of respiratory substrates was discovered by L. Pasteur. In his experiments with yeast in the presence of oxygen, the breakdown of glucose and the intensity of fermentation decreased, but at the same time an intensive growth of biomass was observed. The inhibition of the decomposition of sugars and their more efficient use in the presence of oxygen is called the "Pasteur effect" .. This is explained by the fact that at a high partial pressure of oxygen, the entire pool of ADP and P is spent on the synthesis of ATP. As a result, glycolysis is inhibited due to a decrease in the amount of ADP and P required for substrate phosphorylation, and a high content of ATP inhibits some glycolytic enzymes (phosphofructokinase). As a result, the intensity of glycolysis decreases and synthetic processes (gluconeogenesis) are activated

An important factor determining the rate of cell respiration is the concentration of ADP. The dependence of the rate of oxygen consumption on the concentration of ADP is called respiratory control, or acceptor control of respiration. The ratio of the sum of the concentrations of ATP and 1 / 2ADP to the sum of the concentrations of ATP, ADP, AMP is called energy charge.

An excess of oxygen in plant tissues can occur only locally. In an atmosphere of pure oxygen, respiration of plants decreases, and then the plant dies. This is due to an increase in free radical reactions in cells, oxidation of membrane lipids, and, as a consequence, a violation of all metabolic processes.

2. Carbon dioxide concentration

An increase in the concentration of CO 2 leads to a decrease in the intensity of respiration, because the decarboxylation reactions and the activity of succinate dehydrogenase are inhibited. When acidification of tissues is observed - acidosis.

3. Temperature

Breathing, as an enzymatic process, is temperature dependent. Within certain temperature limits, this dependence obeys the Van't Hoff rule (the rate of chemical reactions doubles when the temperature rises by 10 ° C). For the respiration of each plant species and its organs, there are certain minimum, optimum and maximum temperatures.

4. Water regime

In the leaves of seedlings, with a rapid loss of water, an increase in respiration is noted in the beginning. With a gradual decrease in water cut, this does not happen. Prolonged water deficiency leads to a decrease in respiration. The effect of water is especially clearly traced in the study of seed respiration. When the moisture content of the seeds rises to 14-15%, respiration increases 3-4 times, up to 30-35% - a thousand times. In this case, temperature plays an important role.

5. Mineral nutrition

Adding a salt solution to the water where the seedlings were grown usually increases the respiration of the roots. This effect is called "salt respiration". In tissues of other organs, this effect is not always obtained.

Damage and mechanical stress

Mechanical influences cause short-term increases in oxygen uptake for three reasons: 1) due to the rapid oxidation of phenolic and other compounds that leave the vacuoles of damaged cells and become available for the corresponding oxidases; 2) due to the increase in the amount of substrate for respiration; 3) due to the activation of the processes of restoration of membrane potential and damaged cellular structures.

Breath of plants
Lecture plan

1. general characteristics breathing process.

2. The structure and function of mitochondria.

3. Structure and function of the adenylate system.

4. Respiration Substrates and Respiratory Coefficient.

5. Respiratory pathways

1. General characteristics of the breathing process.

In nature, there are two main processes during which energy sunlight stored in organic matter is released - this is breath and fermentation.

BreathIs a redox process as a result of which carbohydrates are oxidized to carbon dioxide, oxygen is reduced to water, and the released energy is converted into the energy of ATP bonds.

FermentationIs an anaerobic process of decomposition of complex organic compounds into simpler organic substances, also accompanied by the release of energy. During fermentation, the oxidation state of the compounds taking part in it does not change. In the case of respiration, oxygen serves as an electron acceptor, in the case of fermentation, organic compounds.

Most often, the reactions of respiratory metabolism are considered on the example of the oxidative breakdown of carbohydrates.

The overall equation for the reaction of oxidation of carbohydrates during respiration can be represented as follows:

WITH 6 Н12 О6 + 6О2 → 6СО2 + 6 Н2 О + ~ 2874 kJ

2. The structure and function of mitochondria.

Mitochondria are cytoplasmic organelles that are centers of intracellular oxidation (respiration). They contain enzymes of the Krebs cycle, the respiratory electron transport chain, oxidative phosphorylation, and many others.

Mitochondria are 2/3 protein and 1/3 lipids, half of which are phospholipids.

Mitochondrial functions:

1. Carry out chemical reactions, which are the source of electrons.

2. Transfer electrons along the chain of components that synthesize ATP.

3. Catalyze synthetic reactions using the energy of ATP.

4. Regulate biochemical processes in the cytoplasm.

3. The structure and function of the adenylate system.

The metabolism that occurs in living organisms consists of many reactions that occur both with the consumption of energy and with its release. In some cases, these reactions are interrelated. However, most often the processes in which energy is released are separated in space and time from those in which it is consumed. In this regard, all living organisms have developed mechanisms for storing energy in the form of compounds possessing macroergic(energy-rich) connections. The central place in the energy exchange of all types of cells belongs the adenylate system. This system includes adenosine triphosphoric acid (ATP), adenosine diphosphoric acid (ADP), adenosine 5-monophosphate (AMP), inorganic phosphate (P i) and magnesium ions.

4. Respiration substrates and respiratory coefficient

The question of the substances used in the process of respiration has long occupied physiologists. Even in the works of I.P. Borodin (1876) showed that the intensity of the respiration process is directly proportional to the content of carbohydrates in plant tissues. This gave reason to assume that it is carbohydrates that are the main substance consumed during respiration (substrate). In clarifying this question great importance has a definition of the respiratory coefficient.

Respiratory coefficient (DC) is the volumetric or molar ratio of carbon dioxide (CO2) released during respiration to oxygen (O2) absorbed during the same period of time. Respiratory coefficient shows by what products the respiration is carried out.

In addition to carbohydrates, fats, proteins and amino acids, and organic acids can be used as respiratory material in plants.

5. Respiratory pathways

The need to carry out the breathing process under various conditions has led to the development of various pathways of respiratory metabolism in the course of evolution.

There are two main pathways for the conversion of the respiratory substrate, or oxidation of carbohydrates:

1) Glycolysis + Krebs cycle (glycolytic)

2) pentose phosphate (apotomic)

Glycolytic pathway of respiratory metabolism

This path respiratory exchange is the most common and, in turn, consists of two phases.

First phase - anaerobic (glycolysis), localized in the cytoplasm.

Second phase - aerobic, localized in mitochondria.

In the process of glycolysis, the hexose molecule is converted to two molecules of pyruvic acid (PVA):

WITH 6 H12 O6 → 2 C3 H4 O3 + 2H2

The second phase of respiration - aerobic - requires the presence of oxygen. Pyruvic acid enters this phase. General equation this process can be represented as follows:

2PVK + 5 О 2 + Н2 О → 6СО2 + 5Н2 О

Energy balance of the breathing process.

As a result of glycolysis, glucose breaks down into two PVC molecules and two ATP molecules accumulate, two NADH2 molecules are also formed, entering the ETC of respiration, they release six ATP molecules... In the aerobic phase of respiration, 30 ATP molecules are formed.

Thus: 2ATP + 6 ATP + 30 ATP = 38 ATP

Pentose phosphate pathway of respiratory metabolism

There is still an equally common way of glucose oxidation - pentose phosphate. it anaerobic oxidation of glucose, which is accompanied by the release of carbon dioxide CO2 and the formation of NADPH2 molecules.

The cycle consists of 12 reactions in which only phosphoric esters of sugars are involved.

In clarifying this issue, the determination of the respiratory coefficient is of great importance. Respiratory coefficient (DC) is the volume or molar ratio of CO2 released during respiration to that absorbed during the same period of time 02. With normal oxygen access, the DC value depends on the respiration substrate. If carbohydrates are used in the process of breathing, then the process proceeds according to the equation С6Н1206 +602 -> 6С02 + 6Н20. In this case, the DC is equal to one: 6CO2 / 602 = 1. However, if more oxidized compounds, for example, organic acids, undergo decomposition during respiration, oxygen absorption decreases, and the DC becomes greater than unity. So, if malic acid is used as a substrate for respiration, then DC = 1.33. When more reduced compounds, such as fats or proteins, are oxidized during respiration, more oxygen is required and the DC becomes less than unity. So, when using fats, DC = 0.7. Determination of the respiratory coefficients of different plant tissues shows that under normal conditions it is close to unity. This gives reason to believe that, first of all, the plant uses carbohydrates as a respiratory material. With a lack of carbohydrates, other substrates can be used. This is especially evident on seedlings developing from seeds, which contain fats or proteins as a reserve nutrient. In this case, the respiratory coefficient becomes less than one. When used as a respiratory material, fats are broken down to glycerol and fatty acids. Fatty acids can be converted to carbohydrates through the glyoxylate cycle. The use of proteins as a substrate for respiration is preceded by their degradation to amino acids.

32. Anaerobic respiration of plants(glycolysis)

The initial stage of anaerobic decomposition of carbohydrates consists in the formation of a number of phosphorus esters of sugars (hexoses). Glycolysis occurs in the cytoplasm.

Glycolysis occurs in all living cells of organisms. In the process of glycolysis, the hexose molecule is converted to two molecules of pyruvic acid.

At the first stage, the glucose molecule, under the action of the hexokinase enzyme, accepts the remainder of phosphoric acid from ATP, which is converted into ADP, and as a result, glucopyranose-6-phosphate is formed. The latter, under the action of the enzyme phosphohexoisomerase (oxoisomerase), is converted into fructofuranose-6-phosphate. At the further stage of glycolysis of fructofuranose-6-phosphate, another phosphoric acid residue is added to it. The source of energy for the formation of this ether is also the ATP molecule. This reaction is catalyzed by phosphohexokinase activated by magnesium ions. As a result, fructofuranose-1,6-diphosphate and a new molecule of adenosine diphosphate are formed.

The next stage of glycolysis is the oxidation of 3-phosphoglyceric aldehyde by a specific dehydrogenase and the phosphorylation of glyceric acid using mineral phosphoric acid. The 1,3-diphosphoglyceric acid formed as a result of this reaction transfers, with the participation of the phosphoferase enzyme, one phosphoric acid residue to the ADP molecule, which is converted into ATP, thus forming 3-phosphoglyceric acid. The latter, under the action of the enzyme phosphoglyceromutase, is converted into 2-phosphoglyceric acid, which, under the influence of the enzyme of enolase, is converted into phosphoenolpyruvic acid and finally into pyruvic acid.

The formation of pyruvic acid from phosphoenolpyruvate ends the glycolytic cleavage of hexose by the type of alcoholic fermentation.

Krebs cycle

The second phase of breathing - aerobic- localized in the mitochondria and requires the presence of oxygen. Pyruvic acid enters the aerobic phase of respiration.

The process can be divided into three main stages:

1) oxidative decarboxylation of pyruvic acid;

2) cycle tricarboxylic acids(Krebs cycle);

3) the final stage of oxidation - the electron transport chain (ETC) requires the mandatory presence of 0 2.

The first two stages occur in the mitochondrial matrix; the electron transport chain is localized on the inner mitochondrial membrane.

First stage- oxidative decarboxylation of pyruvic acid. This process consists of a series of reactions and is catalyzed by a complex multienzyme system pyruvate decarboxylase. Pyruvate decarboxylase includes three enzymes and five coenzymes (thiamine pyrophosphate, lipoic acid, coenzyme A - KoA-SH, FAD and NAD). As a result of this process, active acetate is formed - acetylcoenzyme A (acetyl-CoA), reduced by NAD (NADH + H +), and carbon dioxide(first molecule). Reduced NAD enters the electron transport chain, and acetyl-CoA enters the tricarboxylic acid cycle.

Second stage- tricarboxylic acid cycle (Krebs cycle). In 1935, the Hungarian scientist A. Szent-Gyorgyi found that the addition of small amounts of organic acids (fumaric, malic or succinic) enhances the absorption of oxygen by crushed tissues. Continuing these studies, G. Krebs came to the conclusion that the main way of oxidation of carbohydrates is cyclic reactions, in which there is a gradual transformation of a number of organic acids. These transformations were called the tricarboxylic acid cycle or the Krebs cycle. The researcher himself was awarded the Nobel Prize for these works in 1953.

The essence of the cycle is in the decarboxylation of pyruvic acid.

Active acetate, or acetyl-CoA, enters the cycle. The essence of the reactions included in the cycle is that acetyl-CoA condenses with oxaloacetic acid (OAA). Further, the transformation proceeds through a series of di- and tricarboxylic organic acids. As a result, PIK regenerates in its previous form. During the cycle, three H2O molecules are attached, two CO2 molecules and four hydrogen pairs are released, which reduce the corresponding coenzymes (FAD and NAD).

Acetyl-CoA, condensing with PUA, gives citric acid, while CoA is released in its previous form. This process is catalyzed by the enzyme citrate synthase. Citric acid is converted to isolic acid. At the next stage, the oxidation of isocitric acid occurs, the reaction is catalyzed by the enzyme isocitrate dehydrogenase. In this case, protons and electrons are transferred to NAD (NADH + H + is formed). This reaction requires magnesium or manganese ions. At the same time, the decarboxylation process takes place. Due to one of the carbon atoms that entered the Krebs cycle, the first CO2 molecule is released. The resulting a-ketoglutaric acid undergoes oxidative decarboxylation. This process is also catalyzed by the multi-enzyme complex ketoglutarate dehydrogenase. As a result, due to the second carbon atom entering the cycle, the second CO2 molecule is released. At the same time, another NAD molecule is reduced to NADH and succinyl-CoA is formed.

At the next stage, succinyl-CoA is split into succinic acid (succinate) and HS-CoA. The energy released in this case is accumulated in the high-energy phosphate bond of ATP. The resulting succinic acid is oxidized to fumaric acid. The reaction is catalyzed by the enzyme succinate dehydrogenase. At the same time, a third hydrogen pair is released, forming FAD-H 2.

At the next stage, fumaric acid, by attaching a water molecule, is converted into malic acid using the enzyme fumarate dehydrogenase. On the last stage cycle, malic acid is oxidized to alkaline acid.

With each stage of the cycle, one molecule of pyruvic acid disappears, and 3 molecules of CO2 and 5 pairs of hydrogen atoms of electrons are split off from different components of the cycle.

A variation of the Krebs cycle is the glyoxylate cycle. Two-carbon compounds, such as acetate, act as a source of carbohydrates, and glyoxylic acid is involved. R-tion of the glyoxylate cycle is the basis for the conversion of stored fat into carbohydrates. The enzymes of this cycle are found in the cells of the cell - glyoxisomes.

In the glyoxylate cycle, in contrast to the Krebs cycle, isocitric acid decomposes into succinic and glyoxylic acids. ... Glyoxylate with the participation of malate synthase interacts with the second molecule of acetyl-Co A, as a result of which malic acid is synthesized, which is oxidized to AAC.

In contrast to the Krebs cycle, in the glyoxylate cycle, not one, but two acetyl-CoA molecules participate in each turnover, and this activated acetyl is used not for oxidation, but for the synthesis of succinic acid. Succinic acid leaves glyoxisomes, turns into PAA and participates in gluconeogenesis (reverse glycolysis) and other biosynthetic processes. The glyoxylate cycle allows you to utilize storage fats, the decomposition of which forms acetyl-CoA molecules. In addition, for every two acetyl-CoA molecules in the glyoxylate cycle.

The physiological meaning of the glyoxylate cycle consists in an additional pathway for the decomposition of fats and the formation of a number of various intermediate compounds that play an important role in biochemical reactions.

Energy of the Krebs cycle

Krebs cycle. plays an extremely important role in the metabolism of the plant organism. It serves as the final stage in the oxidation of not only carbohydrates, but also proteins, fats and other compounds. During the reactions of the cycle, the main amount of energy contained in the oxidized substrate is released, and most of this energy is not lost to the body, but is utilized during the formation of high-energy terminal phosphate bonds of ATP.

In the aerobic phase of respiration, when pyruvic acid is oxidized, 4 NADH + H + molecules are formed. Their oxidation in the respiratory chain leads to the formation of 12 ATP. In addition, one molecule of flavin dehydrogenase (FADH2) is reduced in the Krebs cycle. Oxidation of this compound R in the respiratory chain leads to the formation of 2 ATP, since phosphorylation alone does not occur. During the oxidation of a-ketoglutaric acid molecule to succinic acid, energy is directly accumulated in one ATP molecule (substrate phosphorylation). Thus, the oxidation of one pyruvic acid molecule is accompanied by the formation of 3CO2 and 15 ATP molecules. However, when a glucose molecule breaks down, two pyruvic acid molecules are obtained.

Breath is oxidation organic matter, which is a substrate for respiration. Respiratory substrates are carbohydrates, fats and proteins.

Carbohydrates... In the presence of carbohydrates, most cells use them as substrates. Polysaccharides (starch in plants and glycogen in animals and fungi) are involved in the respiration process only after they have been hydrolyzed to monosaccharides.

Lipids (fats or oils)... Lipids constitute the "main reserve" and are used mainly when the carbohydrate supply is depleted. They must first be hydrolyzed to glycerol and fatty acids. Fatty acids are rich in energy and some cells, for example muscle cells, normally receive part of the energy they need from them.

Squirrels... Since proteins have a number of other important functions, they are used for energy production only after all stores of carbohydrates and fats have been used up, for example, during prolonged fasting (Section 8.9.3). Proteins are pre-hydrolyzed to amino acids, and amino acids are deaminated (they are deprived of their amino groups). The acid formed as a result of deamination is involved in the Krebs cycle or is first converted into fatty acid to then undergo oxidation.

Two types of reactions play a major role in cellular respiration - oxidation and decarboxylation.

Oxidation

In the cell occur oxidative reactions three types.
1. OXIDATION WITH MOLECULAR OXYGEN.

2. HYDROGEN REMOVAL (DEHYDRATION)... In aerobic respiration, glucose oxidation occurs through successive dehydrogenation reactions. The hydrogen removed during each dehydrogenation is used to reduce the coenzyme, which in this case is called the hydrogen carrier:

Most of these reactions occurs in the mitochondria where hydrogen carrier is usually the coenzyme NAD (nicotinamide adenine dinucleotide):

OVER * H ( restored OVER) then undergoes oxidation again with the release of energy. Enzymes that catalyze dehydrogenation reactions are called dehydrogenases. In a series of sequential dehydrogenation reactions, all hydrogen removed from glucose is transferred to hydrogen carriers. This hydrogen is then oxidized by oxygen to water, and the energy released during this is used for ATP synthesis... The phenomenon of energy release during the oxidation (combustion) of hydrogen can be observed if you bring a burning candle to a test tube with hydrogen. This will produce a short, light pop, like a miniature explosion. The same amount of energy is released in the cell, but it is released in a series of redox reactions during the transition of hydrogen from one carrier to another along the so-called respiratory chain.

3. ELECTRON TRANSFER... This happens, for example, during the transition of one ionic form of iron (Fe2 +) to another (Fe3 +)

Electrons can be transferred from one compound to another, like hydrogen in the reactions described above. The connections between which this transfer takes place are called electron carriers. This process takes place in the mitochondria.

Decarboxylation

Decarboxylation- This is the elimination of carbon from a given compound with the formation of CO2. In addition to hydrogen and oxygen, the glucose molecule contains six more carbon atoms. Since the reactions described above only require hydrogen, carbon is removed in the decarboxylation reactions. The resulting carbon dioxide is a by-product of aerobic respiration.