In addition to the 5 kingdoms of wildlife, there are two other kingdoms: prokaryotes and eukaryotes. Therefore, if we consider the systematic position of bacteria, then it will be as follows:
- Empire Cellular.
- Overdrive Nuclear-Free.
- Kingdom of Prokaryota.
- The subdomain of Bacteria.
Why do these organisms stand out in a separate taxon? The thing is that a bacterial cell is characterized by the presence of certain features that impose an imprint on its vital activity and interaction with other creatures and humans.
Bacteria discovery
The discovery of bacterial cells occurred only with the development of technology. Specifically, with the invention in 1695 of a microscope, which gives an increase of 300 times. This was done by Italian Antonio Van Levenguk. The scientist considered droplets of dirty water in his invention and saw that they were simply teeming with the smallest organisms. He called them animalalki.
The proof of their undoubted existence and direct participation in the development of various diseases in humans was made thanks to the experience of Louis Pasteur.
After this discovery, many pathogens were identified and studied. The development of microbiology (the science of microorganisms) took intensive steps forward.
Specifically, what are the structural features of the bacterial cell, their diversity and form, meaning and lifestyle, is being studied by the section of microbiology - bacteriology. Currently, it is closely correlated with other sciences: medical microbiology, molecular biology and biochemistry, biophysics, space biology and others.
Bacterial cell forms
There are several of them.
1 . Spherical, or coccal structures. Subdivided into:
- micrococci - very small, solitary representatives;
- diplococci - the prefix "di" means "two" (that is, bacteria collected in pairs);
- tetracocci - form four-structured organisms;
- streptococci - a colony of spherical microbes collected in a single chain;
- sarcins - form as if a packet of 8, 12 or 16 structures;
- staphylococci - a colony of bacteria in the form of a bunch of grapes.
2. Bacilli, or rod-shaped bacteria. Differ by several criteria.
- in form: right and wrong;
- in size: small, medium or large;
- in the form of end structures: pointed, rounded, chopped off, thickened;
- by grouping and location: solitary, diplobacilli, streptobacteria.
3. Twisted. Are divided into:
- vibrios - slightly curved into a semicircle;
- Spirillas - characterized by a different number of curls.
4. Spirochetes. Are divided into:
- leptospira - in the shape of the letter S;
- Borrelia - up to 12 curls in the structure;
- Treponema - from 12 to 17 curls of small size.
Obviously, a bacterial cell is characterized by the presence of various forms to adapt to any living conditions.
Features of the structural organization
Bacteria are not in vain belong to a separate kingdom of wildlife. People established their inner essence, studied the mechanisms of processes and lifestyle. Therefore, it became clear that there are some structural features of the bacterial cell.
There are several main parts that are required for each representative of this kingdom.
- The presence of a semipermeable cytoplasmic membrane.
- The liquid internal environment is the cytoplasm, in which genetic material and ribosomes are present.
Also, the presence of optional structures is also characteristic of a bacterial cell. Such as:
- cell wall;
- microcapsule;
- inclusion;
- drank;
- capsule;
- disputes;
- flagella;
- pericellular mucus.
Let us consider in more detail what are the structural features of a bacterial cell.
Cell structure
Outside, each bacterium is coated with a cytoplasmic membrane. This structure is a three-layer phospholipid-protein organization. It is very similar in structure and composition to the membrane of an animal cell. When viewed under a microscope, the upper and lower layers are clearly visible, they are darker, composed of phospholipids. Medium - these are proteins that seem to penetrate the entire membrane, therefore they belong to integral ones.
The main function of the cytoplasmic membrane is semipermeability and, as a consequence, selective transport of substances into and out of the cell. It is also a barrier, provides a normal level of osmotic pressure and turgor of the cell (body shape).
A bacterial cell is characterized by the presence of a cytoplasm, a semi-liquid internal environment in which important elements are located. Its composition is presented:
- proteins;
- polysaccharides;
- glycogen granules;
- beta butyric acid;
- volutin.
Special attention should be paid to organelles of cells immersed in the cytoplasm.
Nucleoid and Ribosomes
As in any eukaryotic cell, the bacterial cell has its own genetic apparatus. It is a double-stranded DNA molecule that is one chromosome tightly packed in a ball. This structure is not separated from the cytoplasm by a karyolemma and therefore is called not a nucleus, but a nucleoid.
Additional genetic material distributed in the cytoplasm are structures called plasmids. They are circular DNA molecules, therefore, perform additional hereditary functions of a bacterial cell.
Ribosomes are the smallest structures scattered in large numbers in the cytoplasm. Their nature is represented by RNA molecules. These granules are the material by which you can determine the degree of kinship and the systematic position of a particular type of bacterium. Their function is the assembly of protein molecules.
Capsule
A bacterial cell is characterized by the presence of protective mucous membranes, the composition of which is determined by polysaccharides or polypeptides. Such structures are called capsules. There are micro- and macrocapsules. This structure is formed not in all species, but in the vast majority, that is, it is not mandatory.
What does a capsule protect a bacterial cell from? From phagocytosis by host antibodies if the bacterium is pathogenic. Or from drying out and exposure to harmful substances, if we talk about other types.
Slime and inclusions
Also optional bacteria structures. Mucus, or glycocalyx, is chemically mucoidal polysaccharide. It can form both inside the cell and by external enzymes. It is soluble in water. Purpose: attachment of bacteria to the substrate - adhesion.
Inclusions are microgranules in the cytoplasm of various chemical nature. It can be proteins, amino acids, nucleic acids or polysaccharides.
Motion organoids
Features of a bacterial cell also appear in its movement. For this, flagella are present, which can be in different quantities (from one to several hundred per cell). The basis of each flagellum is the flagellin protein. Thanks to elastic contractions and rhythmic movements from side to side, the bacterium can move in space. The flagellum is attached to the cytoplasmic membrane. Location may also vary between species.
Drank
Even finer than flagella, structures involved in:
- attachment to the substrate;
- water-salt nutrition;
- sexual reproduction.
They consist of pilin protein, their number can reach several hundred per cell.
Similarity to plant cells
Bacterial and plant cells have one undeniable similarity - the presence of a cell wall. However, if it is indisputable in plants, then bacteria are not present in all species, that is, it refers to optional structures.
The chemical composition of the bacterial cell wall:
- peptidoglycan murein;
- polysaccharides;
- lipids;
- squirrels.
Usually this structure has a double layer: outer and inner. Functions are the same as the cell wall of plants. Maintains and denotes a constant body shape and provides mechanical protection.
Dispute formation
What is the structure of the bacterial cell, we examined in sufficient detail. It remains only to mention how bacteria can survive adverse conditions for a very long time without losing viability.
They succeed by forming a structure called a dispute. It is not related to reproduction and only protects bacteria from adverse conditions. The shape of the spores can be different. When normal environmental conditions are restored, the spore is initiated and grows into an active bacterium.