Providing cells with energy. Energy sources

Cells are composed of all living organisms, except viruses. They provide all the processes necessary for the life of plants or animals. 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 cells provide energy? It is based on processes, which we consider below.

Providing cells with energy: how does it happen?

Few cells receive energy from outside, they produce it themselves. Eukaryotic cells have unique "stations". And the source of energy in the cell is mitochondria, the organoid that produces it. It is the process of cellular respiration. Due to this, the cells are provided with energy. However, they are present only in plants, animals and fungi. In cells of bacteria mitochondria are absent. Therefore, their provision of cells with energy is mainly due to the processes of fermentation, rather than respiration.

Structure of mitochondria

It is a two-membrane 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 native DNA and RNA, as well as mitochondrial ribosomes that produce proteins that are necessary for organoids.

The inner membrane possesses outgrowths, which are called cristae, or ridges. The process of cellular respiration occurs on the cristae.

What is inside the two membranes is called the matrix. It contains proteins, enzymes necessary for accelerating chemical reactions, as well as molecules of RNA, 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 the preparatory

During this stage, complex organic compounds are split into simpler ones. So, proteins break down to amino acids, fats to carboxylic acids and glycerin, nucleic acids to nucleotides, and carbohydrates to glucose.

Glycolysis

This is an anoxic stage. 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 in the process of glycolysis breaks down to two molecules of pyruvate. This occurs during ten consecutive chemical reactions. Because of the first five, glucose is phosphorylated, and then split into two phosphotrioses. The next five reactions form two molecules of ATP (adenosine triphosphate) and two molecules of PVK (pyruvic acid). The energy of the cell is stored in the form of ATP.

The whole process of glycolysis can be simplified as follows:

2NAD + 2 ADP + 2H ₃ PO ₄ + C ₆ H ₁₂ O ₆ → 2H ₂ O + 2NAD ^. H ₂ + 2 C ₃ H ₄ O ₃ + 2ATP

Thus, using one glucose molecule, two molecules of ADP and two phosphoric acids, the cell receives two molecules of ATP (energy) and two molecules of pyruvic acid, which it will use in the next stage.

The third stage is oxidation

This stage occurs only in the presence of oxygen. The chemical reactions of this stage occur in the mitochondria. This is the main part of cellular respiration, during which most energy is released. At this stage, pyruvic acid, reacting with oxygen, splits into 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.

Summarizing all the chemical reactions and omitting the details, one can express the whole process of cellular respiration by one simplified equation:

6О ₂ + С ₆ Н ₁₂ О ₆ + 38АДФ + 38Н ₃ РО ₄ → 6СО ₂ + 6Н2О + 38АТФ.

Thus, in the course of respiration from a single molecule of glucose, six molecules of oxygen, thirty-eight molecules of ADP 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

Energy for life activity the cell receives due to respiration - oxidation of glucose, and then pyruvic acid. All these chemical reactions could not pass without enzymes - biological catalysts. Let's look at those of them that are in the mitochondria - the organoids responsible for cellular respiration. They are all called oxidoreductases, because they are needed to ensure the flow of oxidation-reduction reactions.

All oxidoreductases can be divided into two groups:

• Oxidase;
• Dehydrogenase;

Dehydrogenases, in turn, are divided into aerobic and anaerobic. Aerobic contain in their composition coenzyme riboflavin, which the body receives from vitamin B2. The aerobic dehydrogenases contain NAD and NADPH molecules as co-enzymes.

Oxidases are more diverse. First of all, they are divided into two groups:

• Those that contain copper;
• Those in which there is iron.

The first include polyphenol oxidase, ascorbate oxidase, to the second - catalase, peroxidase, cytochrome. The latter, in turn, are divided into four groups:

• Cytochromes a;
• Cytochromes b;
• Cytochromes c;
• Cytochromes d.

Cytochromes a contain ironformorphorphine, cytochromes b - iron protoporphyrin, c - substituted iron mesoporphyrin, d - iron dihydroporphyrin.

Are there other ways of obtaining energy?

Despite the fact that most cells receive it as a result of cellular respiration, there are also anaerobic bacteria, for the existence of which no oxygen is needed. They produce the necessary energy by fermentation. This is a process in which carbohydrates are broken down by 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 in this equation:

C ₆ H ₁₂ O ₆ → C ₂ H ₅ OH + ₂ CO ₂

That is, one molecule of glucose, the bacterium splits up to one molecule of ethyl alcohol and two molecules of carbon monoxide (IV).