Biological oxidation. Oxidation-reduction reactions: examples

Without energy, there is no existence of any living being. After all, every chemical reaction, any process requires its presence. It is easy for any person to understand and feel it. If you do not eat all day, then by evening, and perhaps earlier, the symptoms of increased fatigue, lethargy, and strength will decrease significantly.

How did different organisms adapt to energy? Where does it come from and what processes occur inside the cell? Let's try to understand this article.

Energy production by organisms

Whichever method the energy consumes, the basis is always OBR (redox reactions). Examples can be given different. The equation of photosynthesis, which is carried out by green plants and some bacteria - is also OVR. Naturally, the processes will differ depending on what kind of living being is meant.

So, all animals are heterotrophs. That is, such organisms that are not capable of independently forming ready-made organic compounds within themselves for their further splitting and release of energy of chemical bonds.

Plants, by contrast, are the most powerful producer of organic matter on our planet. They are carrying out a complex and important process called photosynthesis, which consists in the formation of glucose from water, carbon dioxide under the action of a special substance - chlorophyll. A byproduct is oxygen, which is the source of life for all aerobic living beings.

Oxidation-reduction reactions, examples of which illustrate this process:

• 6CO ₂ + 6H ₂ O = chlorophyll = C ₆ H ₁₀ O ₆ + ₆ O ₂ ;

or

• Carbon dioxide + hydrogen oxide under the influence of the chlorophyll pigment (reaction enzyme) = monosaccharide + free molecular oxygen.

There are also representatives of the biomass of the planet who are able to use the energy of chemical bonds of inorganic compounds. They are called hemotropics. They include many kinds of bacteria. For example, hydrogen microorganisms that oxidize substrate molecules in the soil. The process takes place according to the formula: 2H ₂ + 0 ₂ = 2H ₂ 0.

History of the development of knowledge about biological oxidation

The process that underlies the production of energy is now well known. This is a biological oxidation. Biochemistry has so thoroughly studied the subtleties and mechanisms of all stages of action, that there are almost no riddles left. However, this was not always the case.

The first mention of the fact that within the living beings there are complex transformations, which are by nature chemical reactions, appeared around the 18th century. It was at this time that Antoine Lavoisier, the famous French chemist, turned his attention to how biological oxidation and combustion are similar. He traced the approximate path of oxygen absorbed during the respiration and came to the conclusion that oxidation processes take place inside the body, only slower than outside when burning various substances. That is, the oxidizer-oxygen molecules-react with organic compounds, specifically hydrogen and carbon from them, and a complete transformation takes place, accompanied by decomposition of the compounds.

However, even though this assumption is inherently quite real, many things remained unclear. For example:

• Once the processes are similar, then the conditions for their flow must be identical, but the oxidation occurs at a low body temperature;
• The action is not accompanied by the release of a colossal amount of thermal energy and there is no formation of a flame;
• In living beings no less than 75-80% of water, but this does not prevent the "burning" of nutrients in them.

To answer all these questions and understand what is actually a biological oxidation, it took more than one year.

There were different theories that implied the importance of oxygen and hydrogen in the process. The most common and most successful were:

• Bach's theory, called peroxide;
• The theory of Palladin, based on a concept such as "chromogens".

In the future there were still many scientists, both in Russia and other countries of the world, who gradually introduced additions and changes to the question of what is biological oxidation. The biochemistry of our time, thanks to their works, can tell about each reaction of this process. Among the most famous names in this area are the following:

• Mitchell;
• SV Severin;
• Warburg;
• VA Belitser;
• Leninger;
• V. P. Skulachev;
• Krebs;
• Green;
• V. A. Engelhardt;
• Keilin and others.

Types of biological oxidation

There are two main types of the process under consideration, which occur under different conditions. So, the most common way for many types of microorganisms and fungi to transform the food they receive is anaerobic. This biological oxidation, which is carried out without access to oxygen and without its participation in any form. Similar conditions are created where there is no access to air: underground, in rotting substrates, mud, clay, marsh and even in space.

This type of oxidation has another name - glycolysis. It is also one of the stages of a more complex and time-consuming, but energetically rich process - aerobic transformation or tissue respiration. This is the second type of the process under consideration. It occurs in all aerobic living creatures-heterotrophs, which use oxygen for respiration.

Thus, the types of biological oxidation are as follows.

1. Glycolysis, anaerobic pathway. Does not require the presence of oxygen and ends with different forms of fermentation.
2. Tissue respiration (oxidative phosphorylation), or aerobic appearance. Requires the presence of molecular oxygen.

Participants in the process

Let us turn to a consideration of the very features themselves, which includes biological oxidation. Define the main connections and their abbreviations, which we will use in the future.

1. Acetylcoenzyme-A (acetyl-CoA) - a condensate of oxalic acid and acetic acid with coenzyme, formed in the first stage of the tricarboxylic acid cycle.
2. The Krebs cycle (a cycle of citric acid, tricarboxylic acids) is a series of complex consecutive redox transformations, accompanied by the release of energy, the reduction of hydrogen, the formation of important low-molecular products. It is the main link of kata and anabolism.
3. NAD and NAD * H is an enzyme dehydrogenase, decoding as nicotinamide adenine dinucleotide. The second formula is a molecule with attached hydrogen. NADP - nicotinamide adenine dinuclide-phosphate.
4. FAD and FAD * H - flavinadenidine dinucleotide - coenzyme dehydrogenases.
5. ATP - adenosine triphosphoric acid.
6. PVK - pyruvic acid or pyruvate.
7. Succinate or succinic acid, H ₃ PO ₄ - phosphoric acid.
8. GTP - guanosine triphosphate, a class of purine nucleotides.
9. ETC is an electron transport chain.
10. The enzymes of the process: peroxidase, oxygenase, cytochrome oxidase, flavin dehydrogenases, various coenzymes and other compounds.

All these compounds are direct participants in the oxidation process that occurs in the tissues (cells) of living organisms.

Stages of biological oxidation: table

These are all the processes that accompany biological oxidation with the participation of oxygen. Naturally, they are not fully described, but only in essence, since a whole chapter of the book is needed for a detailed description. All the biochemical processes of living organisms are extremely multifaceted and complex.

Oxidation-reduction reactions of the process

Oxidation-reduction reactions, examples of which can illustrate the above described processes of substrate oxidation, are as follows.

1. Glycolysis: monosaccharide (glucose) + 2ADD ⁺ + 2ADP = 2PVK + 2ATP + 4H ⁺ + 2H2O + NADH.
2. Oxidation of pyruvate: PVK + enzyme = carbon dioxide + acetaldehyde. Then the next step: acetaldehyde + Coenzyme A = acetyl-CoA.
3. A lot of sequential transformations of citric acid in the Krebs cycle.

These oxidation-reduction reactions, the examples of which are given above, reflect the essence of the processes occurring only in a general form. It is known that the compounds in question are of high molecular weight or have a large carbon skeleton, so it is simply not possible to depict all the complete formulas.

Energy output of tissue respiration

By the above descriptions it is obvious that it is not difficult to calculate the total yield of all the oxidation by energy.

1. Two molecules of ATP give glycolysis.
2. Oxidation of pyruvate 12 molecules of ATP.
3. 22 molecules account for the cycle of tricarboxylic acids.

The result: complete biological oxidation along the aerobic path gives an energy yield equal to 36 molecules of ATP. The significance of biological oxidation is obvious. It is this energy that is used by living organisms for life and functioning, as well as for warming their body, movement and other necessary things.

Anaerobic oxidation of the substrate

The second type of biological oxidation is anaerobic. That is the one that is carried out by everyone, but on which the microorganisms of certain species stop. This glycolysis, and it is with him clearly discernible differences in the further transformation of substances between aerobes and anaerobes.

The stages of biological oxidation along this path are few.

1. Glycolysis, that is, the oxidation of the glucose molecule to pyruvate.
2. Fermentation, leading to the regeneration of ATP.

Fermentation can be of various types, depending on the organisms that carry it out.

Lactic fermentation

It is carried out by lactic acid bacteria, as well as some fungi. The essence is to restore PVK to lactic acid. This process is used in industry to produce:

• Fermented milk products;
• Pickled vegetables and fruits;
• Silo for animals.

This type of fermentation is one of the most used in human needs.

Alcoholic fermentation

It is known to people since ancient times. The essence of the process is the conversion of PVC into two molecules of ethanol and two carbon dioxide. Due to this output of the product, this type of fermentation is used to produce:

• of bread;
• Wine;
• Beer;
• Confectionery and other.

Its fungi are yeast and microorganisms of bacterial nature.

Oily fermentation

A narrowly specific type of fermentation is sufficient. It is carried out by bacteria of the genus Clostridium. The essence is to convert pyruvate to butyric acid, which gives food products an unpleasant odor and a rancid taste.

Therefore, the reactions of biological oxidation going along such a path are practically not used in industry. However, these bacteria self-seed food and harm, reducing their quality.