Multiple choice

In which of the given organisms, L-lysine replaces meso-diaminopimelic acid in its peptidoglycan?

In most of the prokaryotic organisms, meso-diaminopimelic acid is the intermediator connecting D-glutamic acid molecule to terminal D-alanine residues of tetrapeptide attached to NAM at carboxyl group.

  1. Streptococcus pyogenes

  2. <i style="mso-bidi-font-style:normal">Escherichia coli

  3. <i style="mso-bidi-font-style:normal">Bacillus cereus

  4. Staphylococcus aureus

  5. Clostridium tetani

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D Correct answer
Explanation

Each N-acetylmuramic acid is attached to a short amino acid chain containing L-alanine, D- glutamine, L-lysine and D-alanine with a pentaglycine interbridge between tetrapeptides in the case of Staphylococcus aureus, a gram positive bacterium. Meso-diaminopimelic acid serves as the final precursor in the biosynthesis of L-lysine in both bacteria and higher plants, and is also an essential component of the peptidoglycan of most pathogenic bacteria, nearly all gram-negative and most gram-positive bacteria with the notable exception of Staphylococcus aureus where it is replaced by lysine.