Question

In: Biology

1. a. Describe the structure of peptidoglycan .      b. Describe in detail the architecture and...


1. a. Describe the structure of peptidoglycan .

     b. Describe in detail the architecture and the structure of Gram negative cell wall structure
    
    c. Discuss how Gram positive cell wall is different from Gram negative wall structure. Include all   specific details to score full credit points.
   
    d. What are teichoic acid and their location? Provide role of the teichoic acid in bacterial cells.

Solutions

Expert Solution

A structure of peptidoglycan

Peptidoglycan or murein is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of most bacteria, forming the cell wall. The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh-like layer.It has a crystal lattice structure formed from linear chains of two alternating amino sugars, namely N-acetylglucosamine (GlcNAc or NAGA) and N-acetylmuramic acid (MurNAc or NAMA). The alternating sugars are connected by a β-(1,4)-glycosidic bond. Each MurNAc is attached to a short (4- to 5-residue) amino acid chain, containing L-alanine, D-glutamic acid, meso-diaminopimelic acid, and D-alanine in the case of Escherichia coli (a Gram-negative bacterium) or L-alanine, D-glutamine, L-lysine, and D-alanine with a 5-glycine interbridge between tetrapeptides in the case of Staphylococcus aureus (a Gram-positive bacterium). Peptidoglycan is one of the most important sources of D-amino acids in nature.Cross-linking between amino acids in different linear amino sugar chains occurs with the help of the enzyme DD-transpeptidase and results in a 3-dimensional structure that is strong and rigid. The specific amino acid sequence and molecular structure vary with the bacterial species.

B architectural structure of negative cell wall

It consists of an inner wall composed of peptidoglycan and an outer membrane. Peptidoglycan wall is 2-3nm thick. Three layers of peptidoglycan layer present. Outer layer of gram negative Bacteria is 7nm thick.It Is composed of phospholipids lipoproteins and lipopolysaccharide. Lipoproteins connect the outer membrane to peptidoglycan. Lipopolysaccharide of outer membrane is also called endotoxin. Pore forming proteins called porins are present in outer membrane.Periplasm is the gelatinous material between the outer membrane, the peptidoglycan, and the cytoplasmic membrane. peptidoglycan can prevent cell lysis of gram negative bacteria.

C difference between gram negative cell walll and gram positive Bacteria wall differ

D it is a compound of ribitol and phosphoglycerate. It is present in gram positive Bacteria.

Teichoic acids are found within the cell wall of most Gram-positive bacteria such as species in the genera Staphylococcus, Streptococcus, Bacillus, Clostridium, Corynebacterium, and Listeria, and appear to extend to the surface of the peptidoglycan layer. They can be covalently linked to N-acetylmuramic acid or a terminal D-alanine in the tetrapeptide crosslinkage between N-acetylmuramic acid units of the peptidoglycan layer, or they can be anchored in the cytoplasmic membrane with a lipid anchor.Teichoic acids arr joined to the lipid membrane are referred to as lipoteichoic acids , whereas teichoic acids that are covalently bound to peptidoglycan are referred to as wall teichoic acids .

The main function of teichoic acids is to provide rigidity to the cell-wall by attracting cations such as magnesium and sodium. Teichoic acids can be substituted with D-alanine ester residues,or D-glucosamine, giving the molecule zwitterionic properties. These zwitterionic teichoic acids are suspected ligands for toll-like receptors 2 and 4. Teichoic acids also assist in regulation of cell growth by limiting the ability of autolysins to break the β(1-4) bond between the N-acetyl glucosamine and the N-acetylmuramic acid.Lipoteichoic acids may also act as receptor molecules for some Gram-positive bacteriophage; however, this has not yet been conclusively supported. a contributor negative charge to cell.


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