Question

3. Name the three (3) types of prokaryotes that have the cell walls below: (2 marks) N-acetylglucosamine N-acetylglucosamine N-acetylglucosamine N-acetyltalosaminuronic acid N-acetylmuramic acid N-acetylmuramic acid (NAG) (NAM) (NAG) (NAT) (NAG) (NAM) o Сн, о сн, B-1,3 linkage C © B-1,4 linkage B-1,4 linkage B-1,3 linkage B-1,3 linkage B-1,4 linkage B-1,4 linkage B-1,4 linkage 1 CH2OH | CH2OH | CH OH NH | CH2OH - ỏ i NH CH,OH | CH2OH Сн,он Сн,он O HỌ ...OHKoykoyok ço Roko KOHÓKooKo NHCOCH3 NH NHCOCH3 NHCOCH3 NHCOCH3 H2C-CH HỌC CH O сна CHg L-Glu HO HO NH NH CH L-Ala L-Ala L-Ala L-Lys D-Glu D-Glu L-Glu direct cross-link DAP cross-linked via a glycine pentapeptide L-Lys direct cross-link D-Ala D-Ala a. Which of these is/are susceptible to lysozyme (a, b, c)?

Answer 1

Solution: Prokaryotes are single-cellular organisms that contain free genetic material with no membrane bound cell-organelles in the cytoplasm. All Gram-negative bacteria, Gram-positive bacteria and Archaebacteria fall under this category.

All of them consist of cell membrane and cell wall surrounding and protecting their cell.

The cell wall composition varies in Gram-positive, Gram-negative and Archaebacteria. The primary component of cell wall is peptidoglycan that consists of polymers of alternating amino-sugar residues connected with glycosidic bonds. Each of these sugars have amino acid side chain residues which can be further crosslinked to give a mesh-like structure.

a) Prokaryote: Gram-positive bacterium ( For example, Staphylococcus aureus).

The peptidoglycan in their cell wall consist of amino sugars: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). NAG and NAM are linked together by B-1,4 glycosidic bond. NAM contains a tetrapeptide side chain (L-Ala, D-Glu, L-Lys, D-Ala). These tetrapeptide side chains are crosslinked together by pentaglycine linkage.

b) Prokaryote: Archaebacteria (Example, Methanopyrus).

The peptidoglycan in their cell wall consist of amino sugars: N-acetylglucosamine (NAG) and N-acetyltalosaminuronic acid (NAT). NAG and NAT are joined by B-1,3 glycosidic bond. NAT contains a tetrapeptide side chain (L-Glu, L-Ala, L-Lys, L-Glu). These tetrapeptide side chains are crosslinked together by direct linkage.

c) Prokaryote: Gram-negative bacterium (For example, Escherichia coli).

The peptidoglycan in their cell wall consist of amino sugars: N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). NAG and NAM are linked together by B-1,4 glycosidic bond. NAM contains a tetrapeptide side chain (L-Ala, D-Glu, meso-diaminopimelic acid, D-Ala). These tetrapeptide side chains are crosslinked together by direct linkage.

Lysozyme is an enzyme that attacks and breaks B-1,4 glycosidic bond between the amino sugars present in peptidoglycan. Hence, a and c are susceptible to lysozyme breakdown.