Bacteria ("stick" from ancient Greek)represent a kingdom (group) of non-nuclear (prokaryotic) microorganisms, unicellular, as a rule. Today, about ten thousand of their species are known and described. Scientists suggest that there are more than a million of them.
A bacterial cell may have a round, crimped,bacillary shape. In rare cases, there are cubic, tetrahedral, stellate, and also O- or C-shaped forms. Appearance defines the abilities that a bacterial cell possesses. For example, depending on the form, microorganisms possess some degree of mobility, the ability to attach to the surface, in one way or another, the absorption of nutrient compounds.
The bacterial cell includes three obligatory structures: a cytoplasmic membrane, a ribosome and a nucleoid.
From the membrane from the outsideseveral layers. In particular, there is a slimy cover, capsule, cell wall. In addition, different surface structures develop from the outside: villi, flagella. The cytoplasm and membrane are united in the concept of "protoplast."
Bacterial cell with all its contentsis limited from the external environment by means of a membrane. Inside, in a homogeneous fraction of the cytoplasm, proteins, soluble RNAs, substrates for exchange reactions, various compounds are located. The rest contains different structural elements.
Bacterial cell does not contain nuclear membranesand any other intra-cytoplasmic membranes that are not derived from the cytoplasmic membrane. At the same time, for some prokaryotes local "protrusions" of the main shell are characteristic. These "protrusions" - mesosomes - perform various functions and separate the bacterial cell into functionally different parts.
All the data necessary for life,are contained in one DNA. The chromosome, which includes a bacterial cell, usually has a ring-shaped, covalently-closed. At one point, DNA is attached to the membrane and placed in a separate, but not separated from the cytoplasm, structure. This structure has the name "nucleoid". In expanded form, the bacterial chromosome has a length of more than a millimeter. It is usually presented in a single copy. In other words, prokaryotes are almost all haploid. However, under certain specific conditions, the bacterial cell may contain copies of its chromosome.
Particular importance in the life of a bacteriumhas a cell wall. At the same time, this structural element is not mandatory. In the laboratory, some forms of prokaryotes were obtained, in which the wall was absent completely or partially. These bacteria could exist under normal conditions, but in some cases they lost the ability to divide. In nature, there is a group of prokaryotes that do not contain walls in their structure.
On the outer surface of the wall,place an amorphous layer - capsule. Mucous layers are separated from the microorganism quite easily, they have no connection with the cell. Cases also have a fine structure, they are not amorphous.
Reproduction of bacteria of some formsis carried out by means of an equal, binary cross-section or budding. Different groups have different variants of division. So, for example, in cyanobacteria, reproduction occurs in a multiple way - several consecutive binary divisions. As a result, from four to a thousand new microorganisms are formed. They have special mechanisms through which the plasticity of the genotype is necessary to adapt to the changing environment and evolution.
