Fig. 4: Synthesis of Peptidoglycan Monomers
and Action of Bactoprenol, Step 2

Peptidoglycan monomers are synthesized in the cytosol of the bacterium where they attach to a membrane carrier molecule called bactoprenol. The bactoprenols transport the peptidoglycan monomers across the cytoplasmic membrane and helps insert them into the growing peptidoglycan chains.

a. First, N-acetylglucosamine (NAG) links up with uridine diphosphate (UDP) to form UDP-NAG. Some of the NAG is enzymatically converted to N-acetylmuramic acid (NAM) forming UDP-NAM.

b. Five amino acids are sequentially added to the UDP- NAM forming a pentapeptide. The last two are D-alanine molecules enzymatically produced from L-alanine, the usual form of the amino acid.

c. The NAM-pentapeptide is attached to the bactoprenol carrier molecule in the cytoplasmic membrane, the energy being supplied by one of the high-energy phosphate groups of the UDP.

d. The NAG is attached to the NAM-pentapeptide on the bactoprenol to complete the peptidoglycan monomer.

Bactoprenols then insert the peptidoglycan monomers into the breaks in the peptidoglycan at the growing point of the cell wall.

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