Without energy, not a single living being can exist. After all, every chemical reaction, every process requires its presence. It is easy for anyone to understand and feel this. If you do not eat food all day, then by the evening, and possibly even earlier, symptoms of increased fatigue, lethargy will begin, strength will decrease significantly.
How have different organisms adapted to obtain energy? Where does it come from and what processes take place inside the cell? Let's try to understand this article.
Getting energy by organisms
Whatever way creatures consume energy, ORR (oxidation-reduction reactions) are always the basis. Various examples can be given. The equation of photosynthesis, which is carried out by green plants and some bacteria, is also OVR. Naturally, the processes will differ depending on which living being is meant.
So, all animals are heterotrophs. That is, such organisms that are not able to independently form ready-made organic compounds within themselves fortheir further splitting and release of the energy of chemical bonds.
Plants, on the contrary, are the most powerful producer of organic matter 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. The by-product is oxygen, which is the source of life for all aerobic living things.
Redox reactions, examples of which illustrate this process:
6CO2 + 6H2O=chlorophyll=C6H 10O6 + 6O2;
or
carbon dioxide + hydrogen oxide under the influence of 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:
History of the development of knowledge of biological oxidation
The process that underlies energy production is well known today. This is biological oxidation. Biochemistry has studied the subtleties and mechanisms of all stages of action in such detail that there are almost no mysteries left. However, this was notalways.
The first mention of the most complex transformations occurring inside living beings, which are chemical reactions in nature, appeared around the 18th century. It was at this time that Antoine Lavoisier, the famous French chemist, turned his attention to how similar biological oxidation and combustion are. He traced the approximate path of oxygen absorbed during breathing and came to the conclusion that oxidation processes occur inside the body, only slower than outside during the combustion of various substances. That is, the oxidizing agent - oxygen molecules - react with organic compounds, and specifically, with hydrogen and carbon from them, and a complete transformation occurs, accompanied by decomposition of the compounds.
However, although this assumption is inherently quite real, many things remained incomprehensible. For example:
- since the processes are similar, then the conditions for their occurrence should be identical, but oxidation occurs at low body temperature;
- the action is not accompanied by the release of a huge amount of thermal energy and there is no flame formation;
- living beings contain at least 75-80% water, but this does not prevent the "burning" of nutrients in them.
It took years to answer all these questions and understand what biological oxidation really is.
There were different 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, calledperoxide;
- 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 biological oxidation is. Modern biochemistry, thanks to their work, can tell about every reaction of this process. Among the most famous names in this area are the following:
- Mitchell;
- S. V. Severin;
- Warburg;
- B. A. Belitzer;
- Leninger;
- B. P. Skulachev;
- Krebs;
- Greene;
- B. A. Engelhardt;
- Kailin and others.
Types of biological oxidation
There are two main types of the process under consideration, which proceed under different conditions. So, the most common way of converting the food received in many species of microorganisms and fungi is anaerobic. This is 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, 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 living creatures-heterotrophs, whichoxygen is used for breathing.
So the types of biological oxidation are as follows.
- Glycolysis, anaerobic pathway. Does not require the presence of oxygen and results in various forms of fermentation.
- Tissue respiration (oxidative phosphorylation), or aerobic view. Requires the presence of molecular oxygen.
Participants in the process
Let's move on to the consideration of the very features that biological oxidation contains. Let's 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, formed at the first stage of the tricarboxylic acid cycle.
- The Krebs cycle (citric acid cycle, tricarboxylic acids) is a series of complex sequential redox transformations accompanied by the release of energy, hydrogen reduction, and the formation of important low molecular weight products. It is the main link in cata- and anabolism.
- NAD and NADH - dehydrogenase enzyme, stands for nicotinamide adenine dinucleotide. The second formula is a molecule with an attached hydrogen. NADP - nicotinamide adenine dinucleotide phosphate.
- FAD and FADN − flavin adenine dinucleotide - coenzyme of dehydrogenases.
- ATP - adenosine triphosphoric acid.
- PVC - pyruvic acid or pyruvate.
- Succinate or succinic acid, H3PO4− phosphoric acid.
- GTP − guanosine triphosphate, class of purine nucleotides.
- ETC - electron 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 lies in the oxygen-free splitting of monosaccharides, which precedes the process of cellular respiration and is accompanied by an energy output equal to two ATP molecules. Pyruvate is also formed. This is the initial stage for any living organism of a heterotroph. Significance in the formation of PVC, which enters the cristae of mitochondria and is a substrate for tissue oxidation by oxygen. In anaerobes, after glycolysis, fermentation processes of various types begin. |
| Pyruvate oxidation | This process consists in the conversion of PVC formed during glycolysis into acetyl-CoA. It is carried out using a specialized enzyme complex pyruvate dehydrogenase. The result is cetyl-CoA molecules that enter the Krebs cycle. In the same process, NAD is reduced to NADH. Place of localization - cristae of mitochondria. |
| The breakdown of beta fatty acids | This process is carried out in parallel with the previous one onmitochondrial cristae. Its essence is to process all fatty acids into acetyl-CoA and put it in the tricarboxylic acid cycle. This also restores NADH. |
| Krebs cycle |
Begins with the conversion of acetyl-CoA to citric acid, which undergoes further transformations. One of the most important stages that includes biological oxidation. This acid is exposed to:
Each process is done several times. Result: GTP, carbon dioxide, reduced form of NADH and FADH2. At the same time, biological oxidation enzymes are freely located in the matrix of mitochondrial particles. |
| Oxidative phosphorylation | This is the last step in the conversion of compounds in eukaryotic organisms. In this case, adenosine diphosphate is converted to ATP. The energy required for this is taken from the oxidation of those NADH and FADH2 molecules that were formed in the previous stages. Through successive transitions along the ETC and a decrease in potentials, energy is concluded in macroergic bonds of ATP. |
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 whole chapter of the book is needed for a detailed description. 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 2O + NADH.
- Pyruvate oxidation: PVC + enzyme=carbon dioxide + acetaldehyde. Then the next step: acetaldehyde + Coenzyme A=acetyl-CoA.
- Many successive transformations of citric acid in the Krebs cycle.
These redox reactions, examples of which are given above, reflect the essence of the ongoing processes only in general terms. It is known that the compounds in question are either high molecular weight or have a large carbon skeleton, so it is simply not possible to represent everything with full formulas.
Energy output of tissue respiration
From the above descriptions, it is obvious that it is not difficult to calculate the total energy yield of the entire oxidation.
- Glycolysis produces two ATP molecules.
- Pyruvate oxidation 12 ATP molecules.
- 22 molecules per citric acid cycle.
Bottom line: complete biological oxidation through the aerobic pathway gives an energy output equal to 36 ATP molecules. The importance 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 bodies, movement and other necessary things.
Anaerobic oxidation of the substrate
The second type of biological oxidation is anaerobic. That is, one that is carried out by everyone, 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.
There are few biological oxidation steps along this pathway.
- Glycolysis, that is, the oxidation of a glucose molecule to pyruvate.
- Fermentation leading to ATP regeneration.
Fermentation can be of different types, depending on the organisms involved.
Lactic acid fermentation
Carried out by lactic acid bacteria and some fungi. The bottom line is to restore PVC to lactic acid. This process is used in industry to obtain:
- fermented milk products;
- fermented vegetables and fruits;
- animal silos.
This type of fermentation is one of the most used in human needs.
Alcohol fermentation
Known to people since antiquity. The essence of the process is the conversion of PVC into two molecules of ethanol and two carbon dioxide. Due to this product yield, this type of fermentation is used to obtain:
- bread;
- wine;
- beer;
- confectionery and more.
It is carried out by fungi, yeast and microorganisms of a bacterial nature.
Butyric fermentation
A rather narrowly specific type of fermentation. Carried out by bacteria of the genus Clostridium. The bottom line is the conversion of pyruvate into butyric acid, which gives food an unpleasant odor and rancid taste.
Therefore, biological oxidation reactions following this path are practically not used in industry. However, these bacteria sow food on their own and cause harm, lowering their quality.
