All living organisms except viruses are composed of cells. They provide all the necessary processes for the life of a plant or animal. The cell itself can be a separate organism. And how can such a complex structure live without energy? Of course not. So how does the supply of cells with energy occur? It is based on the processes that we will discuss below.
Providing cells with energy: how does this happen?
Few cells receive energy from outside, they produce it themselves. Eukaryotic cells have a kind of "stations". And the source of energy in the cell is mitochondria - the organoid that produces it. The process of cellular respiration takes place in it. Due to it, the cells are provided with energy. However, they are present only in plants, animals and fungi. In the cells of bacteria, mitochondria are absent. Therefore, they provide cells with energy mainly due to fermentation processes, and not respiration.
The structure of mitochondria
This is a two-membered organoid that appeared in a eukaryotic cell during evolution as a result of its absorption of a smaller prokaryotic cell. This can explain the fact that mitochondria contain their own DNA and RNA, as well as mitochondrial ribosomes, which produce proteins necessary for organoids.
The inner membrane has outgrowths called cristae, or ridges. On cristae, the process of cellular respiration occurs.
What is inside two membranes is called a matrix. It contains proteins, enzymes necessary to accelerate chemical reactions, as well as RNA molecules, DNA and ribosomes.
Cellular respiration is the basis of life
It takes place in three stages. Let's look at each of them in more detail.
The first stage is preparatory
During this stage, complex organic compounds are broken down into simpler ones. So, proteins break down to amino acids, fats to carboxylic acids and glycerol, nucleic acids to nucleotides, and carbohydrates to glucose.
Glycolysis
This is an oxygen-free phase. It consists in the fact that the substances obtained during the first stage are split further. The main sources of energy that the cell uses at this stage are glucose molecules. Each of them decomposes into two pyruvate molecules during glycolysis. This occurs during ten consecutive chemical reactions. Due to the first five, glucose is phosphorylated and then broken down into two phosphotrioses. In the following five reactions, two molecules of ATP (adenosine triphosphoric acid) and two molecules of PVA (pyruvic acid) are formed. The energy of the cell is stored in the form of ATP.
The whole process of glycolysis can be simplified depicted in this way:
2NAD + 2ADP + 2H 3 PO 4 + C 6 H 12 O 6 â 2H 2 O + 2 NAD . H 2 + 2C 3 H 4 O 3 + 2 ATF
Thus, using one glucose molecule, two ADP molecules and two phosphoric acid, the cell receives two ATP molecules (energy) and two pyruvic acid molecules, which it will use in the next step.
Third Stage - Oxidation
This stage occurs only in the presence of oxygen. Chemical reactions of this stage occur in mitochondria. This is precisely the main part of cellular respiration, during which the most energy is released. At this stage, pyruvic acid, reacting with oxygen, breaks down to water and carbon dioxide. In addition, 36 ATP molecules are formed. So, we can conclude that the main sources of energy in the cell are glucose and pyruvic acid.
Summing up all chemical reactions and omitting details, we can express the whole process of cellular respiration with one simplified equation:
6 2 + 6 12 6 + 38 + 38 3 4 â 6 2 + 62 + 38.
Thus, during breathing from one glucose molecule, six oxygen molecules, thirty-eight ADP molecules and the same amount of phosphoric acid, the cell receives 38 ATP molecules, in the form of which energy is stored.
Variety of mitochondrial enzymes
The cell receives energy for life due to respiration - oxidation of glucose, and then pyruvic acid. All these chemical reactions could not have taken place without enzymes â biological catalysts. Let's look at those that are in the mitochondria - the organoids responsible for cellular respiration. All of them are called oxidoreductases, because they are needed to ensure the occurrence of redox reactions.
All oxidoreductases can be divided into two groups:
Dehydrogenases, in turn, are divided into aerobic and anaerobic. Aerobic ones contain coenzyme riboflavin, which the body receives from vitamin B2. Aerobic dehydrogenases contain NAD and NADP molecules as coenzymes.
Oxidases are more diverse. First of all, they are divided into two groups:
- those containing copper;
- those containing iron.
The former include polyphenol oxidases, ascorbate oxidase, and the latter include catalase, peroxidase, and cytochromes. The latter, in turn, are divided into four groups:
- cytochrome a;
- cytochrome b;
- cytochrome c;
- cytochromes d.
Cytochromes a contain ironformylporphyrin, cytochromes b - iron protoporphyrin, c - substituted iron mesoporphyrin, d - iron dihydroporphyrin.
Are there other ways to get energy?
Despite the fact that most cells get it as a result of cellular respiration, there are also anaerobic bacteria for the existence of which oxygen is not needed. They produce the necessary energy through fermentation. This is a process in which carbohydrates are broken down with the help of enzymes without the participation of oxygen, as a result of which the cell receives energy. There are several types of fermentation, depending on the final product of chemical reactions. It can be lactic acid, alcoholic, butyric acid, acetone-butane, citric acid.
For example, consider alcohol fermentation. It can be expressed as follows:
C 6 H 12 O 6 â C 2 H 5 OH + 2CO 2
That is, a bacterium breaks down one molecule of glucose into one molecule of ethyl alcohol and two molecules of carbon monoxide (IV).