Respiration in prokaryotes

Respiration in prokaryotes

Energy metabolism (catabolism) is a flow of reactions accompanied by the mobilization of energy and its transformation into an electrochemical or chemical form, which can then be used in all energy – dependent processes.

There are groups of prokaryotes whose energy metabolism is not associated with the transformation of organic compounds (prokaryotes with photolithotrophic and chemolithotrophic types of energy metabolism). In relation to this kind of energy processes, the term "catabolism" is not applicable. They have only one flow of transformations of organic carbon compounds – the anabolic one.

The energy processes of prokaryotes significantly exceed the biosynthetic processes in terms of their volume (scale), and their course leads to significant changes in the environment. Various and unusual in this respect are the possibilities of prokaryotes, the ways of their energetic existence. All this combined has focused the researchers ' attention primarily on studying the energy metabolism of prokaryotes.

Multiple Choice

Energy metabolism is called ...

• anabolism

• assimilation

• catabolism

Multiple Choice

What is energy metabolism?

• is a flow of reactions accompanied by the mobilization of energy and its transformation into an electrochemical form, which can then be used in all energy – dependent processes.

• is a flow of reactions accompanied by the mobilization of energy and its transformation into an electrochemical or chemical form, which can then be used in all energy – dependent processes.

• is a flow of reactions accompanied by the mobilization of energy and its transformation into a chemical form, which can then be used in all energy – dependent processes.

Energy resources. 

Organisms may not use all the types of energy that exist in nature. Nuclear, mechanical, and thermal types of energy are inaccessible to them. In order for heat to serve as a source of energy, a large temperature difference is necessary, which is impossible in living organisms. The external sources of energy (energy resources) available to living systems are electromagnetic (physical) energy (light of a certain wavelength) and chemical (reduced chemical compounds). The ability to use light energy is possessed by a large group of photosynthetic organisms, including prokaryotes, which have photoreceptor molecules of several types (chlorophylls, carotenoids, phycobiliproteins).

For all other organisms, the energy sources are the processes of oxidation of chemical compounds. Often, energy resources are biopolymers in the environment (polysaccharides, proteins, nucleic acids), as well as lipids. Before being used, biopolymers must be hydrolyzed to their constituent monomeric units. This stage is very important for the following reasons.

Proteins and nucleic acids are extremely diverse. The number of types of proteins is estimated in the thousands, after hydrolysis, only 20 amino acids are formed. The whole variety of nucleic acids (DNA and RNA) after hydrolysis is reduced to 5 types of nucleotides. Thus, the breakdown of polymers to monomeric units dramatically reduces the set of chemical molecules that can be used by the body.

Multiple Choice

The external sources of energy (energy resources) available to living systems are

• only electromagnetic (physical) energy (light of a certain wavelength).

• only chemical (reduced chemical compounds).

• electromagnetic (physical) energy (light of a certain wavelength) and chemical (reduced chemical compounds).

Polymer molecules are broken down to monomers by enzymes synthesized and released by prokaryotes into the environment (exoenzymes). Starch and glycogen are hydrolyzed by amylases, and cellulose glycosidic bonds are cleaved by cellulase. Many bacteria form pectinase, chitinase, agarase, and other enzymes that hydrolyze the corresponding polysaccharides and their derivatives. Proteins are broken down by extracellular proteases acting on peptide bonds. Nucleic acids are hydrolyzed by ribonucleases and deoxyribonucleases.

The resulting small molecules are easily transported into the cell through the membrane. The process of breakdown of fatty acids is localized in the cell and includes several stages. In the first step, the fatty acid is converted by the corresponding enzyme to a CoA-derivative, which is oxidized in the-position, followed by cleavage of acetyl-CoA. Another reaction product is a CoA derivative of a fatty acid, shortened by two carbon atoms. Acetyl-CoA is used through catabolic channels to provide energy to the cell.