Bacterial Cell Structure and Reproduction Mechanisms
The Plasma Membrane
The structure of the bacterial plasma membrane is similar to the 75 Å thick unitary membrane found in eukaryotic cells. However, its composition varies slightly, notably lacking lecithin and sterols. The membrane invaginates into the cell to form structures called mesosomes.
Functions of the Plasma Membrane
- Acts as a selective barrier.
- Contains enzymes responsible for synthesizing bacterial cell wall components.
- Mesosomes facilitate the formation of partitions during cell division.
- Contains enzymes that perform cellular respiration.
The Bacterial Cell Wall
The cell wall is composed of carbohydrates and peptides. Its primary component is murein, a peptidoglycan network formed by polysaccharides.
Main Functions of the Cell Wall
- Maintains bacterial shape against changes in osmotic pressure.
- Acts as a semipermeable membrane, regulating ion passage.
- Provides resistance against the action of certain antibiotics.
The Capsule
The capsule is essentially composed of polysaccharides. Its primary functions include:
- Protection against desiccation.
- Protection against infection by bacteriophages.
Flagella
Some bacteria possess flagella, which allow for movement. These structures are simpler than those found in eukaryotic cells, are very thin and long, and consist of a protein called flagellin.
Pili and Fimbriae
These are hollow, tubular protein structures found on the surface of some Gram-negative bacteria.
- Fimbriae: Short and numerous; they allow bacteria to attach to substrates.
- Pili: Long structures; usually only one or two appear per bacterium.
Protoplasm or Hyaloplasm
This is the internal environment of the bacteria, consisting of a colloid in which ribosomes, hereditary material, and other components are immersed.
Hereditary Material
The hereditary material consists of a double-stranded, circular DNA molecule. Due to the lack of complex nucleoprotein organization, it is referred to as naked DNA or the nucleoid. Additionally, bacteria may contain small, circular DNA molecules that replicate independently of the chromosome, known as plasmids.
Bacterial Reproduction
Bacteria reproduce asexually via transverse binary fission:
- The bacterial chromosome replicates in association with the mesosome, with two copies remaining anchored at points near the mesosome.
- The plasma membrane expands, increasing the distance between the two chromosome copies.
- A partition forms, dividing the stem cell into two daughter cells, each receiving a copy of the DNA.
Furthermore, bacteria exhibit parasexual mechanisms, through which genetic information is transferred horizontally between cells.