Pili, Cytoplasmic Membrane
- hair-like microfibrils usually produced by flagellated gram negative bacteria observable under electron microscope
- composed of CHON called Pilin
- 2 types:
a. Sex/ Fertility Pili - sexual conjugation and transfer of genetic material
b. Somatic/ Ordinary/ Common Pili - adhesion of bacterial cell to the host cell, thus, contributing to virulence
Cytoplasmic Membrane (in bacteria)
- also called Cell Membrane
- Composed of phospholipid and proteins which is the site of energy production in bacteria
- FUnctions :
a. Maintains selective permeability and transport of solutes
b. Electron transport and oxidative phosphorylation to aerobic species
c. Excretion of hydrolytic enzymes
d. Bears the enzymes and carrier molecules that function in biosynthesis of DNA, cell wall polymers and membrane lipids
e. Bears the receptors and other proteins of the chemotactic and other sensory transduction system.
Bacterial Anatomy: Cell Walls!
Up first in my anatomical survey of bacterial structures is the cell wall! Bacteria’s cell walls are extremely important to cell survival. Without the thick enclosure protecting the cell, the osmotic pressure within the cell (due to all the solutes dissolved in the cytoplasm) would cause it to lyse.
Depending on how thick the cell wall is, bacteria are lumped into two large categories: Gram-positive and Gram-negative. Gram-positive bacteria have thicker cell walls while Gram-negative bacteria have thinner cell walls. This difference causes the two groups to stain different colors when treated with the Gram stain technique and can be used to help identify unknown bacteria.
The cell wall is made up of a polysaccharide called peptidoglycan. This molecule is made up of N-acetylglucosamine and N-acetylmuramic acid as well as a few amino acids. These smaller molecules link together to form long chains of peptidoglycan. These long chains are then used to form a sheet around the cell.
The way in which the peptidoglycan molecules are linked is different for Gram-positive and Gram-negative bacteria. In Gram-negative bacteria, the cross-linkage occurs between the amino group of one amino acid and the carboxyl group of another.
In Gram-positive bacteria, the cross-linkage is caused by an interpeptide bridge made of glycine molecules.
Gram-positive bacteria also have teichoic acids embedded in the cell wall. These are covalently bonded to the muramic acid present in the wall. Teichoic acids help account for the cell wall’s negative charge due to the presence of phosphate in the molecules and they bind Ca2+ and Mg2+ to facilitate transport into the cell.
Not all microbes have cell walls! Some bacteria, such as the mycoplasmas, and some Archaea naturally lack cell walls. These microbes have other ways to protect themselves from lysis, either by having robust cytoplasmic membranes or they live in habitats that are osmotically protected.