Q67. Bacterial cell lysis by lysozyme is due to the

1. Hydrolysis of α-1,4-glycosidic bonds between the N-acetylglucosamine and N-acetylmuramic acid
2. Inhibition of cell wall synthesis
3. Hydrolysis of pentapeptide bridges
4. Hydrolysis of β-1,4-glycosidic bonds between the N-acetylglucosamine and N-acetylmuramic acid

   Bacterial Cell Lysis by Lysozyme: Correct Answer and Detailed Explanation

   Lysozyme causes bacterial cell lysis by specifically hydrolyzing β-1,4-glycosidic bonds in the peptidoglycan layer of bacterial cell walls. This action weakens the cell wall structure, leading to osmotic rupture, particularly in Gram-positive bacteria.

   Correct Answer

   The precise mechanism is hydrolysis of β-1,4-glycosidic bonds between the N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) in peptidoglycan. Lysozyme acts as a glycoside hydrolase, cleaving these bonds in the glycan backbone of the bacterial cell wall, which compromises structural integrity and triggers lysis due to osmotic pressure.

   Peptidoglycan Structure

   Bacterial peptidoglycan consists of repeating disaccharide units of NAG and NAM linked by β-1,4-glycosidic bonds, with peptide cross-links providing rigidity. Lysozyme targets the bond between the C1 of NAM (or NAG) and C4 of the adjacent NAG (or NAM), creating gaps that destabilize the wall.

   Option Analysis

   Option	Description	Correct/Incorrect	Explanation
   Hydrolysis of α-1,4-glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acid	Cleavage of α-1,4 bonds linking NAG and NAM.	Incorrect	Peptidoglycan bonds are β-1,4, not α-1,4; α-linkages occur in other polysaccharides like starch, not bacterial walls.
   Inhibition of cell wall synthesis	Blocks new peptidoglycan formation (e.g., like penicillin).	Incorrect	Lysozyme degrades existing peptidoglycan via hydrolysis, not preventing synthesis.
   Hydrolysis of pentapeptide bridges	Breaks peptide cross-links between glycan chains.	Incorrect	Lysozyme targets glycosidic bonds, not peptides; proteases like autolysins handle peptide bridges.
   Hydrolysis of β-1,4-glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acid	Cleavage of β-1,4 bonds linking NAG and NAM.	Correct	This is the exact mechanism: lysozyme hydrolyzes β-1,4 linkages between NAM and NAG, disrupting peptidoglycan.

   Mechanism Overview

   Lysozyme binds peptidoglycan in its active site cleft, using Glu35 and Asp52 residues for acid-base catalysis to hydrolyze the β-1,4 bond. This is most effective against Gram-positive bacteria due to their thick peptidoglycan layer; Gram-negatives resist via outer membrane barriers.