Water as the basis of vital activity
The aqueous environment forms the overwhelming part of the bacterial cell. The fluid inside the microorganism can be in a free or bound state. The mechanical function of water is to maintain the necessary intracellular pressure (turgor), and the chemical function is to ensure that hydrolysis reactions take place.
Upon moisture loss, metabolic processes freeze, and the cell stops reproducing. This property is widely used in practice: the method of lyophilization (vacuum drying of a pre-frozen culture) allows strains to be preserved for a long time, since the microbe does not die, but merely enters a state of dormancy.
Dry residue: proteins and carbohydrates
The remaining 10% of the mass forms the dry residue of the microorganism. Its composition is distributed extremely unevenly among macromolecules:
| Component | Proportion in dry residue |
|---|---|
| Proteins | 52% |
| Carbohydrates | 17% |
| RNA | 16% |
| Lipids | 9% |
| DNA | 3% |
| Minerals | 3% |
Proteins act as the dominant component. They catalyze biochemical transformations (enzymatic role) and build the most important elements of the cell: the cytoplasmic membrane, cell wall, capsules, spores, and flagella. Bacterial proteins contain unique compounds absent in human tissues, for example, diaminopimelic acid and D-isomers of amino acids.
Carbohydrates are represented by the full spectrum of sugars (from mono- to polysaccharides) and easily form complex bonds with lipids and proteins. They participate in the construction of the cell wall, are deposited in the form of reserve starch and glycogen, and also determine the antigenic specificity of the bacterium.
Lipids and nucleic acids
Lipids are concentrated in the cell wall of gram-negative microbes and in the cytoplasmic membrane (CPM). They serve as a reserve energy source and form somatic antigens, including endotoxins (lipopolysaccharides). Fatty acids with a long chain (C14–C18) predominate in the lipid composition. Acid-fast bacteria are distinguished by a high content of waxes and mycolic acid, while mycoplasmas are the only prokaryotes whose CPM contains sterols.
Nucleic acids are responsible for genetic information and protein synthesis:
- RNA is present in messenger, transfer, and ribosomal forms. Free nucleotides not only build polymer chains, but also are part of coenzymes.
- DNA consists of two antiparallel strands (5'→3' and 3'→5' direction). The helix is held together by hydrogen bonds according to the principle of complementarity (adenine is complementary to thymine, guanine to cytosine). A DNA monomer consists of deoxyribose, a phosphate group, and a nitrogenous base.
Minerals and ions
Analysis of bacterial ash shows the presence of macronutrients (nitrogen, sulfur, phosphorus, calcium, potassium, magnesium, iron) and micronutrients (copper, zinc, barium, cobalt).
Key organogens perform basic metabolic tasks:
- Nitrogen (N): necessary for the synthesis of proteins and nucleotides.
- Sulfur (S): forms sulfhydryl groups that stabilize the spatial structure of proteins.
- Phosphorus (P): is part of the structure of nucleic acids and provides energy metabolism (ATP).
Metal ions act as activators for enzymes (magnesium, manganese, iron) and ribosomes (potassium, magnesium). To capture and transport iron from the external environment, bacteria possess specific carrier molecules called siderophores.
Briefly: answers to topical questions
Which specific coenzymes include free nucleotides of the bacterial cell?
Free purine and pyrimidine nucleotides act as crucial structural components of coenzymes in the cell. The sources present the following nucleotide-based coenzymes:
- FAD and NAD+ — include nucleotides as organic molecules involved in catalysis.
- Coenzyme A (CoA) — contains an adenylyl nucleotide in its active form (as a 3-phosphoadenosine-5-diphosphate residue).
What types of reserve nutrient inclusions do bacteria form besides starch and glycogen?
The sources explicitly indicate lipids as reserve nutrients. Volutin is designated as a cytoplasmic inclusion; its reserve function is not confirmed in the cited sources. Volutin granules are localized at the poles of the cell and can give it a club-like shape; they exhibit metachromasia.
To remember unique lipid components, use the "Two M" association: Mycobacteria are rich in mycolic acid, while Mycoplasmas are the only ones that have sterols in their membrane.
Class and exam questions
What will happen to a bacterial cell when water is removed?
Reproduction and metabolic reactions will stop, but the cell will not die. This principle is the basis for microbial preservation via lyophilization.
Which protein components are present in bacteria but absent in humans?
Bacterial cells contain specific D-isomers of amino acids and diaminopimelic acid.
Why do bacteria need siderophores?
These are specialized molecules that bind iron ions in the external environment and transport them into the cell as soluble complexes.
What else to study on this topic
- Lyophilization of microorganisms: mechanisms of drying and viability preservation
- Structure and toxic properties of lipopolysaccharides (LPS)
- Antigenic specificity of bacterial polysaccharides
- Complementarity principle and antiparallelism of microbial DNA chains
- Taxonomic significance of GC-pair analysis in microbiology
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