Question

Matching drug and mode of action 37. Penicillins and cephalosporins 38. Sulfonamides 39. Aminoglycosides 40. Amphotericin B 41. Acyclovir A) are metabolic analogs of PABA and block folic acid synthesis B) inhibits the DNA polymerase of herpesvirus C) block transpeptidases that cross-link peptidoglycan molecules D) attach to the 30S ribosomal subunit and disrupt protein synthesis in the 70S ribosome E) binds to fungal ergosterol

Answer 1

Penicillin & cephalosporin	Blocks transpeptidase that cross link peptidoglycan molecule They consists of beta-lactam ring and inhibit bacterial growth. The peptidoglycan is one of the important components of bacterial cell wall and it provides rigidity and support. The beta lactam ring of bacteria binds to the transpeptidase and blocks its function and hence it prevents the cross-linking of peptidoglycan. This inhibition of cross linking prevents formation of new cell wall which makes it permeable and kills the bacteria. They mostly work against gram positive bacteria as they have thick wall but not lipopolysaccharide layer.
Sulfonamides	Are metabolic analogs of PABA and block folic acid synthesis The sulfonamides are structural analogues of PABA and hence it inhibits the folate synthase and hence it blocks the production of folic acid. It is a bacteriostatic and hence prevents bacterial growth. When the sulfonamide is present, it prevents the bacteria from using the folic acid and hence prevents its growth and hence is unable to reproduce. Due to the inability to produce folic acid, it prevents metabolic process of bacteria.
Aminoglycosides	Attach to 30S ribosomal subunit and disrupt protein synthesis in 70S ribosome. They tend to attach and bind to the 16S ribosomal rRNA that is localized within the 30S subunit. Due to this it leads to inhibition of translocation of peptidyl tRNA from A to P-site. Due to this it causes mRNA misreading and hence prevents the synthesis of 70S subunit of ribosome.
Amphotericin B	Binds to fungal ergosterol They bind to the ergosterol and hence it leads to loss of membrane permeability to small molecules and metabolites. As it bind to ergosterol which is an important component of cell membrane of fungus, it starts to form pores causing membrane leakage. It tends to cause leakage and movement of ions like K+, Na+, H+ and Cl etc and hence subsequently leads to the death of the fungi.
Acyclovir	Inhibit the DNA polymerase of herpesvirus The acyclovir is a nucleoside analog which tends to inhibit replication of the herpes simplex virus. It tends to bind to the DNA polymerase of herpesvirus simplex virus and presents the replication. It acts as analog to deoxyguanosine triphosphate (dGTP) and since it does not contain the 3’-0H group, it does not allow the attachment of other nucleotide unit and hence prevents replication.