Without energy, no living creature can exist. After all, every chemical reaction, any process requires its presence. It is easy for any person to understand this and feel it. If you don’t eat food all day, then in the evening, and perhaps earlier, symptoms of increased fatigue, lethargy will begin, and strength will significantly decrease.
How did different organisms adapt to the production of energy? Where does it come from and what processes occur inside the cell? Let's try to understand this article.
Getting energy by organisms
Whatever way the creatures consume energy, they are always based on OVR (redox reactions). There are various examples. 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 creature is meant.
So, all animals are heterotrophs. That is, such organisms that are not able to independently form ready-made organic compounds inside themselves for their further breakdown and release of energy of chemical bonds.
Plants, by contrast, are the most powerful organic producer on our planet. It is they who carry 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. By-product is oxygen, which is the source of life for all aerobic living things.
Redox reactions, examples of which illustrate this process:
- 6CO 2 + 6H 2 O = chlorophyll = C 6 H 10 O 6 + 6O 2 ;
or
- carbon dioxide + hydrogen oxide under the influence of the chlorophyll pigment (reaction enzyme) = monosaccharide + free molecular oxygen.
There are also such representatives of the planet’s biomass that are able to use the energy of chemical bonds of inorganic compounds. They are called chemotrophs. These include many types of bacteria. For example, hydrogen microorganisms that oxidize substrate molecules in the soil. The process takes place according to the formula: 2 2 +0 2 = 2 2 0.
The history of the development of biological oxidation knowledge
The process that underlies energy production is well known today. This is biological oxidation. Biochemistry has so thoroughly studied the intricacies and mechanisms of all stages of action that there are almost no mysteries. However, this was not always the case.
The first mention of the fact that complex transformations occur within living beings, which are chemical reactions by nature, 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 followed the approximate path of oxygen absorbed during respiration and came to the conclusion that oxidation processes occur inside the body, only slower than outside when various substances are burned. That is, the oxidizing agent - oxygen molecules - reacts with organic compounds, and specifically, with hydrogen and carbon from them, and a complete conversion occurs, accompanied by decomposition of the compounds.
However, even though this assumption is inherently quite realistic, many things remained incomprehensible. For instance:
- since the processes are similar, then the conditions for their course must be identical, but oxidation occurs at a low body temperature;
- the action is not accompanied by the release of an enormous amount of thermal energy and the formation of a flame does not occur;
- in living beings, at least 75-80% of water, but this does not interfere with the “burning” of nutrients in them.
It took several years to answer all these questions and understand what biological oxidation actually means.
There were various theories that implied the importance of the presence of oxygen and hydrogen in the process. The most common and most successful were:
- Bach's theory called peroxide;
- Palladin’s theory, based on the concept of “chromogens”.
In the future, there were many more scientists, both in Russia and other countries of the world, who gradually made additions and changes to the question of what is biological oxidation. Biochemistry of our time, thanks to their work, can tell about each reaction of this process. Among the most famous names in this area are the following:
- Mitchell;
- S.V. Severin;
- Warburg
- V. A. Belitser;
- Leninger;
- V.P. Skulachev;
- Krebs
- Green
- W. A. Engelhardt;
- Cailin and others.
Types of biological oxidation
Two main types of the process under consideration can be distinguished, which proceed under different conditions. So, the most common way in many types of microorganisms and fungi is to convert the food received - anaerobic. This is biological oxidation, which is carried out without the access of oxygen and without its participation in any form. Similar conditions are created where there is no access to air: underground, in rotting substrates, silts, clays, swamps, and even in space.
This type of oxidation has another name - glycolysis. It is also one of the stages of a more complex and laborious, but energetically rich process - aerobic transformation or tissue respiration. This is the second type of process under consideration. It occurs in all aerobic heterotroph living creatures that use oxygen for respiration.
Thus, the types of biological oxidation are as follows.
- Glycolysis, anaerobic pathway. It does not require the presence of oxygen and ends in various forms of fermentation.
- Tissue respiration (oxidative phosphorylation), or aerobic form. Requires the presence of molecular oxygen.
Process participants
We proceed to consider directly the very features that biological oxidation encompasses. We define the main compounds and their abbreviations, which we will use in the future.
- Acetylcoenzyme-A (acetyl-CoA) is a condensate of oxalic and acetic acid with a coenzyme that forms at the first stage of the tricarboxylic acid cycle.
- The Krebs cycle (a cycle of citric acid, tricarboxylic acids) is a series of complex sequential redox transformations accompanied by the release of energy, the reduction of hydrogen, and the formation of important low molecular weight products. It is the main link of kata and anabolism.
- NAD and NAD * N is an enzyme dehydrogenase, which stands for nicotinamide adenine dinucleotide. The second formula is a molecule with attached hydrogen. NADP - nicotinamide adenine dinucleotide phosphate.
- FAD and FAD * N - flavin adenine dinucleotide - coenzyme dehydrogenases.
- ATP - adenosine triphosphoric acid.
- PVC - pyruvic acid or pyruvate.
- Succinate or succinic acid, H 3 PO 4 - phosphoric acid.
- GTP - guanosine triphosphate, a class of purine nucleotides.
- ETC - electronic transport chain.
- Enzymes of the process: peroxidases, oxygenases, cytochrome oxidases, 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.
Biological oxidation stages: table
| Stage | Processes and meaning |
| Glycolysis | The essence of the process is the oxygen-free breakdown of monosaccharides, which precedes the process of cellular respiration and is accompanied by an energy release equal to two ATP molecules. Pyruvate is also formed. This is the initial stage for any living organism of the heterotroph. The value in the formation of PVA, which enters the mitochondrial cristae and is a substrate for tissue oxidation by oxygen. In anaerobes, after glycolysis, different types of fermentation occur. |
| Pyruvate Oxidation | This process consists in the conversion of the PVC formed during glycolysis to acetyl-CoA. It is carried out using a specialized pyruvate dehydrogenase enzyme complex. The result is cetyl-CoA molecules that enter the Krebs cycle. In the same process, NAD is restored to NADH. Place of localization - mitochondrial crista. |
| The breakdown of beta fatty acids | This process is carried out in parallel with the previous mitochondrial cristae. Its essence is to process all fatty acids into acetyl-CoA and put it in the tricarboxylic acid cycle. At the same time, NADH is also being restored. |
| Krebs cycle | It begins with the conversion of acetyl-CoA to citric acid, which undergoes further transformations. One of the most important stages, which includes biological oxidation. This acid is exposed to: - dehydrogenation;
- decarboxylation;
- regeneration.
Each process takes place several times. Result: GTP, carbon dioxide, reduced form of NADH and FADH 2 . Moreover, biological oxidation enzymes are freely located in the matrix of mitochondrial particles. |
| Oxidative Phosphorylation | This is the last stage in the conversion of compounds in eukaryotic organisms. In this case, adenosine diphosphate is converted to ATP. The energy required for this is taken during the oxidation of those NADH and FADN 2 molecules that were formed in the previous stages. By successive transitions along the ETC and lowering the potentials, energy is converted into macroergic ATP bonds. |
These are all processes that accompany biological oxidation with the participation of oxygen. Naturally, they are not fully described, but only in essence, since a detailed chapter requires a whole chapter of the book. All biochemical processes of living organisms are extremely multifaceted and complex.
Redox reactions of the process
Redox reactions, examples of which can illustrate the processes of substrate oxidation described above, are as follows.
- Glycolysis: monosaccharide (glucose) + 2NAD + + 2ADP = 2PVC + 2ATP + 4H + + 2H 2 O + NADH.
- Pyruvate oxidation: PVC + enzyme = carbon dioxide + acetaldehyde. Then the next step: acetaldehyde + Coenzyme A = acetyl-CoA.
- Many consecutive transformations of citric acid in the Krebs cycle.
These redox reactions, examples of which are given above, reflect the essence of the processes only in a general form. It is known that the compounds in question relate to high molecular weight or having a large carbon skeleton; therefore, it is simply not possible to depict everything in full formulas.
Tissue respiration energy output
According to the above descriptions, it is obvious that it is not difficult to calculate the total yield of all oxidation by energy.
- Two ATP molecules produce glycolysis.
- Pyruvate oxidation of 12 ATP molecules.
- 22 molecules fall on the tricarboxylic acid cycle.
Bottom line: complete biological oxidation via the aerobic pathway gives an energy yield equal to 36 ATP molecules. 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 your body, movement and other necessary things.
Anaerobic substrate oxidation
The second type of biological oxidation is anaerobic. That is, the one that is carried out at all, but on which microorganisms of certain species stop. This is glycolysis, and it is from it that the differences in the further transformation of substances between aerobes and anaerobes are clearly traced.
The stages of biological oxidation along this path are few.
- Glycolysis, i.e. the oxidation of a glucose molecule to pyruvate.
- Fermentation leading to ATP regeneration.
Fermentation can be of various types, depending on the organisms that carry it.
Lactic acid fermentation
It is carried out by lactic acid bacteria, as well as some fungi. The bottom line is to restore the PVC to lactic acid. This process is used in industry to obtain:
- dairy products;
- pickled vegetables and fruits;
- silo for animals.
This type of fermentation is one of the most used in human needs.
Alcohol fermentation
Known to people from antiquity. The essence of the process is the conversion of PVC into two ethanol molecules and two carbon dioxide. Due to this product yield, this type of fermentation is used to obtain:
- of bread;
- wine
- beer
- confectionery and other things.
Yeast and microorganisms of a bacterial nature carry it out.
Butyric acid fermentation
Quite narrowly specific type of fermentation. It is carried out by bacteria of the genus Clostridium. The bottom line is turning pyruvate into butyric acid, which gives the food an unpleasant odor and rancid taste.
Therefore, biological oxidation reactions proceeding along this path are practically not used in industry. However, these bacteria themselves sow food and harm, lowering their quality.