Definition of Bacterial Structure

Viviana Villamil Ramirez
Lic. in Biology and Chemistry. M.Sc. in Biotechnological Processes

In biology, we start from the idea that the form is derived from the function, so the structures of organisms respond to an evolutionary pattern, where they best perform a function determined. Bacteria are a clear example of this, which is why they have different morphologies. Bacteria present the following structures: Cytoplasmic membrane, cell wall, superficial layers, hairs, fimbrins, cell inclusions, gas vesicles, endospores and flagella.

An ovoid-shaped bacterium is called coccus and when its shape is cylindrical it is called bacillus. Between these two groups there are variations such as spirilla, which are spiral-shaped bacilli. Other cells remain clustered after cell division and form clumps of long chains such as streptococcus or groupings in the form of clusters of grapes such as staphylococcus.

The size of prokaryotes varies between 0.2 µm and 700 µm and has an inverse relationship with the speed of their metabolism, since in very large cells the Nutrient transport processes can be inefficient and qualify the microorganism as uncompetitive compared to those that have a size minor. In addition to this, the small cells have a greater surface area, which favors a greater exchange of nutrients with the medium and a higher growth rate.

Cytoplasmic membrane

The cytoplasmic membrane is a structure that surrounds the cell and which functions as a barrier from the external environment and protects the contents of the cytoplasm. Another of its functions is the exchange of nutrients and the excretion of cellular waste products, which is why it presents a selective permeability. The cytoplasmic membrane is formed by a double layer of phospholipids (phospholipid bilayer) where the Phospholipids or fatty acids have hydrophobic characteristics and glycerol-phosphate has hydrophobic characteristics. hydrophilic.

The hydrophilic ends interact with the external environment and the cytoplasm, while the phospholipids create a hydrophobic environment inside the membrane. The stability of said membrane is generated from ionic bonds and hydrogen bonds. Attached to this, the membrane has different types of associated proteins; the periplasmic ones that are in contact with the external environment, allow the union to different substrates or the transport of substances to the cell, others are integral proteins that are fully associated with the membrane, enzymes that catalyze bioenergetic reactions, transport proteins membrane; that allow three transport systems: simple transport, group translocation and ABC transport. In the first, only the presence of a protein is required, in the second; a group of proteins that help in transport is required and the transported molecule is phosphorylated and in the third it binds to three proteins; one that binds to the substrate, another that transports the molecule, and a third that generates energy for transport.

The cell's energy is produced in the cytoplasmic membrane, since the membrane can present an energetically charged by the separation of H+ and OH- ions, so it can supply different cellular functions that require energy. It is important to mention that the membrane also has the function of excreting proteins, since many of them hydrolyze different substrates in order to obtain glucose.

Cellular wall

The cell wall is another bacterial structure that aims to prevent cell lysis by internal cell pressure, promote shape and rigidity. The cell walls of bacteria are made of peptidoglycan, a polysaccharide linked to a small group of amino acids. This structure determines whether the bacterium is gram positive or gram negative, since in gram positive bacteria peptidoglycan represents the 90% of the cell wall and in gram-negative cells it represents only 10%, complemented by a layer of lipopolysaccharide, this lipopolysaccharide layer can contain endotoxins that cause diseases for animals such as pathogenic bacteria of the genders Salmonella, shigella and Escherichia that cause toxic intestinal symptoms, due to its membrane. Gram-negative bacteria also have proteins called porins in their cell wall, which function as channels for the transport of hydrophilic substances. Some prokaryotic cells can live without a cell wall and are called protoplasts.

Other determining structures

Superficial layers, hairs and fimbrins They are structures that are formed from the secretion of different viscous substances. The capsules and mucous layers are not part of the cell wall, but their functions are the fixation of cells to solid surfaces, biofilm formation, generate protection by means of the capsules in the pathogenic bacteria so as not to be phagocytosed by the cells of the system immune. Fimbrins and hairs are structures formed by proteins and also have different functions such as; fixation, reception and mobility.

Bacteria often have cell inclusions that function as an energy or storage reserve, among them you can find poly-β-hydroxybutyric acid (PHB), glycogen, polyphosphate, magnetosomes.

The gas vesicles They are present in planktonic bacteria, where these structures have the function of providing buoyancy to the microorganism and allowing them to be suspended at different depths. being a favorable strategy for phototrophic bacteria, since when floating they can be located at a strategic angle so that light reaches them and carry out the process of photosynthesis. Each vesicle is composed of two different proteins.

The endospores They are structures that are born by a process called sporulation and are a survival mechanism. since they are resistant to heat, chemical substances, desiccation, nutrient limitation, among others.

The bacterial flagella They are long and thin structures that are attached to the cell at one end with a helical shape. This structure allows the rotary movement of the cell with the help of energy from the proton motive force. The formation of the flagellum is given by a series of genes associated with the movement of the microorganism and can move at speeds greater than 60 times the length of the flagellum. cell per second, thus exceeding the speed of movement of the cheetah, since it can move 25 times faster than the length of its size per second.