Bacterial cell wall composition3 Bacterial cell wall compositionBacterial cell wall composition: Chemically speaking, bacterial cell wall is made up of carbohydrates, proteins, lipids, inorganic salts, phosphorus, diaminopimelic acid and muramic acid (derivatives of glucose). The rigid layer in the cell wall of bacteria is known as peptidoglycan or merein. They constitute as much as 95% of the cell wall in Gram positive bacteria while in gram negative bacteria it accounted for only 5-10%.  Each layer of peptidoglycan is a thin sheets of two sugar derivatives, N acetyl glucosamine and N acetyl muramic acid and a small group of tetrapeptide consisting of  L-alanine, D-alanine, D-glutamate and either lysine or diaminopimelic acid. The rigidity of the cell wall is provided by glycosidic bond between two sugar derivatives. In gram negative bacteria the cell wall is more complex in nature than in gram positive bacteria. It contains upto 20% lipids while in Gram positive bacteria it contains only traces of lipids.

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on 14 December 2012 in Bacterial Cell Wall

Bacterial cell wall resistant: Many bacterial species produce an outer covering called a capsule.  The capsule is made of An endospore of bacteria showing the core cortex and coat2 300x210 Bacterial cell wall resistantpolysaccharides that cling to the surface of the cell and protect it against drying or harsh chemicals. Some bacteria have a special means of surviving difficult conditions.  When living condition become unfavorable , some bacteria form special  dehydrated cells called endospores. The completed endospore consists of multiple layers of resistant coats (including a cortex, a spore coat, and sometimes an exosporium) surrounding a nucleoid, some ribosomes, RNA molecules, and enzymes. Bacterial endospores are resistant to antibiotics, most disinfectants, and physical agents such as radiation, boiling, and drying. The impermeability of the spore coat is thought to be responsible for the endospore’s resistance to chemicals.

 

The heat resistance of endospores is due to a variety of factors:

  • Calcium-dipicolinate, abundant within the endospore may stabilize and protect the endospore’s DNA.
  • Small acid-soluble proteins saturate the endospore’s DNA and protect it from heat, drying, chemicals, and radiation.
  • The cortex may osmotically remove water from the interior of the endospore and the dehydration that results is thought to be very important in the endospore’s resistance to heat and radiation.

on 30 November 2012 in Bacterial Cell Wall

 

Synthesis of peptydoglycan of bacterial cell wall 265x300 Bacterial cell wall synthesisSyntheis of bacterial cell wall: The main chemical composition of bacteria is peptydoglycan. The peptidoglycan monomers are synthesized in the cytosol and are then attached to a membrane carrier bactoprenol. Bactoprenol transports peptidoglycan monomers across the cell membrane where they are inserted into the existing peptidoglycan. In the first step of peptidoglycan synthesis, the glutamine donates an amino group to a sugar, fructose 6-phosphate. This turns fructose 6-phosphate into glucosamine-6-phosphate. In second step, an acetyl group is transferred from acetyl CoA to the amino group on the glucosamine-6-phosphate creating N-acetyl-glucosamine-6-phosphate. In step three of the synthesis process, the N-acetyl-glucosamine-6-phosphate is isomerized, which will change N-acetyl-glucosamine-6-phosphate to N-acetyl-glucosamine-1-phosphate. In step four, the phosphate-N-acetyl-glucosamine-1-phosphate attacks UTP( Uridine triphosphate). In step five, some of the UDP-N-acetyl-glucosamine (UDP-GlcNAc) is converted to UDP-MurNAc (UDP-N acetylmuramic acid) by the addition of a lactyl group to the glucosamine. Step six occurs in the cytoplasmic membrane where a lipid carrier called bactoprenol carries peptidoglycan precursors through the cell membrane. Bactoprenol will attack the UDP-MurNAc penta, creating a PP-MurNac penta, which is now a lipid. UDP-GlcNAc is then transported to MurNAc, creating Lipid-PP-MurNAc penta-GlcNAc, a disaccharide, also a precursor to peptidoglycan. The next reaction is known as tranglycosylation. In the reaction, the hydroxyl group of the GlcNAc will attach to the MurNAc in the glycan, which will displace the lipid-PP from the glycan chain where transglycosylase enzyme plays important role.

 

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on 20 November 2012 in Bacterial Cell Wall

:
The cell wall of bacteria has at least three major functions:
1. Constrains the internal volume
2. Defines the shape of the cell
3. Anchor point to extracellular projections such as flagella.

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on 17 September 2012 in Bacterial Cell Wall

Bacteria showing cell wall 300x240 Bacterial cell wall structure: The thick, rigid and elastic structure of bacteria present below the capsules, sheaths and flagella and external to the cell membrane of the cell that gives shape to the cell is known as cell wall. Cell wall is accounted for 10-40% of dry weight of the cell. The cell wall of some bacteria can be stain by crystal violet and iodine (gram stain). On the basis of composition, bacteria can be divided into two major groups i.e. gram positive and gram negative bacteria. Electron micrograph shows that cell wall of Gram positive cells is (20-25 nm) thick than the cell wall of gram negative bacteria (10-15 nm). Gram positive cells stain purple due to retention of the crystal violet dye during the Gram stain. Gram negative bacteria do not retain the primary dye in Gram stain and hence appear pink. Gram negative bacteria have an additional outer membrane which is the major permeability barrier. The space between the inner and outer membranes is known as the periplasmic space, which contains digestive enzymes and other transport proteins.

on 16 September 2012 in Bacterial Cell Wall

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