Antibacterial Agents: Protein Synthesis

Question 1

Name the three binding sites on a ribosome

Answer 1

Where new charged tRNA molecules first attach, where growing peptide chain is held, where uncharged tRNA molecules leave

Question 2

How many ribosomal subunits do bacteria have

Answer 2

50S + 30S subunits

Question 3

What is the start codon in bacteria called?

Answer 3

F-Met

Question 4

What antibacterial agents act on the 30S subunit?

Answer 4

Aminoglycoside antibiotics and tetracyclines

Question 5

What antibacterial agents act on the 50S subunit?

Answer 5

Chloramphenicol and macrolides

Question 6

Give two examples of aminoglycosides drugs?

Answer 6

Streptomycin and Gentamicin

Question 7

Describe Aminoglycosides’ mechanism of action.

Answer 7

Prevent initiation by preventing binding of start codon, cause misreading of codons along mRNA and interferes with translocation of tRNA from A to P site

Question 8

What type of bacteria do aminoglycosides have activity against?

Answer 8

Gram -ve aerobic bacilli

Question 9

Why are aminoglycosides not absorbed in the GIT

Answer 9

Highly polar - don’t readily cross cell membranes

Question 10

How are aminoglycosides administered?

Answer 10

Topically (I.V. or I.M.)

Question 11

Where are aminoglycosides mainly distributed?

Answer 11

To the extracellular fluid (do not cross BBB)

Question 12

Do aminoglycosides undergo metabolism?

Answer 12

No

Question 13

How are aminoglycosides exctreted?

Answer 13

Glomerular filtrartion

Question 14

What type of aminoglycoside is toxic and why?

Answer 14

Neomycin. It is nephrotoxic

Question 15

What are aminoglycosides clinical uses?

Answer 15

G -ve bacillary infections, bacterial endocarditis, TB, plague, conjunctiva or external ear infections

Question 16

What are the side effects of aminoglycosides?

Answer 16

Ototoxicity, neuromuscular transmission inhibition, paralysis, nephrotoxicity, contact dermatitis, bone marrow depression and hemolytic toxicity

Question 17

What are the main mechanisms of resistance of aminoglycosides?

Answer 17

Membrane impermeabilization, bacterial expression of drug inactivating enzymes (plasmids), inhibitors of cell wall synthesis and alteration of receptor protein on 30S subunit by mutations

Question 18

What are tetracyclines?

Answer 18

Bacteriostatic antibiotics (30S)

Question 19

What is tetracyclines mechanism of action?

Answer 19

Bind irreversibly to 30S - competes with tRNA for A site
Prevents elongation of polypeptide chain

Question 20

What type of bacteria do tetracyclines act on?

Answer 20

G+ve/G-ve bacteria, spirochaetes and protozoa - wide spectrum

Question 21

How are tetracyclines administered?

Answer 21

Orally and by I.V.

Question 22

Where are tetracyclines distributed?

Answer 22

Everywhere

Question 23

How are tetracyclines metabolized?

Answer 23

Undergo 2nd generation metabolism in the liver

Question 24

How are tetracyclines excreted?

Answer 24

Kidneys in urine and doxycycline glucuronide is excreted via bile

Question 25

What are tetracyclines clinal uses?

Answer 25

Peptic ulcer disease, Lymes disease, cholera, mycoplasma pneumoniae, chlamydia, acne and chronic hynonatraemia

Question 26

What are tetracyclines side effects?

Answer 26

GIT disturbances, photosensitivity, deposition in calcified tissues, hepatotoxicity, vestibular dysfunction, Fanconi syndrome, pseudotumor cerebri and hematologic toxicity

Question 27

How is bacteria resistant to tetracyclines?

Answer 27

Efflux pumps, enzymatic inactivation and ribosomal protection