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MSK Week 2 > 2.2.2. Antibiotics II > Flashcards

2.2.2. Antibiotics II Flashcards

1
Q

Eukaryotic vesus Prokaryotic Ribosomes

A

Eukaryotic: 60S + 40S = 80S
Prokaryotic: 50S + 30S = 70S
*Structural differences are one basis for selective toxicity

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2
Q

Mitochondria and Selective Toxicity

A

Mitochondria have their own DNA and their own ribosomes (ribosomes are more similar to bacterial ribosomes than to eukaryotic ones). Therefore, if antibiotic diffuses across all membranes this can be a problem

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3
Q

Components of the 30S ribosomal subunit

A
  • one rRNA molecule (16S)

- 21 different proteins (S1-S21)

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4
Q

Components of the 50S ribosomal subunit

A
  • two rRNA molecules (5S and 23S)

- 31 different proteins (L1-L31)

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5
Q

3 Basic Steps of Protein Synthesis

A
  1. Amino acid activation
  2. Formations of Initiation complexes (30S and 70S)
  3. Polypeptide Chain Synthesis
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6
Q

Amino acid activation

A

aka “Charging” of tRNA by the enzyme aminoacyl-tRNA synthetase

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7
Q

Formation of Initiate Complexes

A

Step 1: charged tRNA, mRNA and 30S ribosomal subunit (includes IFs and GTP) bind
Step 2: the 50S binds and creates the 70S complex

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8
Q

4 Steps of Polypeptide Chain Synthesis

A
  1. Recognition
  2. Peptidyl Transfer
  3. Translocation
  4. Release
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9
Q

Antibiotics that target amino acid activation

A

NONE, unable to achieve selective toxicity

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10
Q

Antibiotics that target the initiation complexes

A

Oxazolidinones prevent the formation of the 70S ribosomal ternary complex by binding to the 50S ribosomal subunit

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11
Q

Linezolid (Zyvox)

A

The first of a new class of antibiotics called oxazolidinones (binds to 50S), used to treat Gram-positive infections

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12
Q

Is linezolid bacteriostatic or bactericidal?

A

BOTH: it is bacteriostatic for staphylococci and enterococci, but is is bactericidal for streptococci (strong/irreversible interaction b/w drug and 50S = bactericidal)

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13
Q

Antibiotics that are inhibitors of recognition

A

Aminoglycosides: prevent codon, anti-codon recognition

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14
Q

Aminoglycosides

A 
Targets specific proteins in the 30S ribosomal subunit:
Streptomycin,
Kanamycin,
Tobramycin,
Gentamicin,
Neomycin,
Amikacin,
Paramomycin, etc.
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15
Q

3 Mechanisms of Streptomycin

A
  1. Misreading
  2. Cyclic Polysomal Blockade
  3. Faulty Outer Membrane Proteins
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16
Q

Misreading (streptomycin)

A

A-site becomes distorted (leads to inactive ribosomes or incorrect amino acid insertion)

17
Q

Cyclic Polysomal Blockade (streptomycin)

A

Although the 70S complex forms, it is unstable and falls apart b/c streptomycin is bound to 30S

18
Q

Faulty Outer Membrane Proteins (streptomycin)

A

Translational misreading leads to mutant outer membrane proteins that make the bacterial membrane leaky (more drug leaks into the cell and acts at the 30S complex)

19
Q

Benefits of Aminoglycoside therapy

A
  1. Rapid bactericidal effect
  2. Broad spectrum
  3. Effective against Pseudomonas
20
Q

Drawbacks of Aminoglycoside therapy

A
  1. Resistance
  2. Ototoxicity and nephrotoxicity
  3. Antagonized by anaerobiasis, low pH, and ions
  4. Ineffective against most intracellular bacteria
  5. Induce bacterial biofilm formation
21
Q

Ways to develop resistance to Aminoglycosides

A
  1. Altered target in 30S ribosomal subunit
  2. Decreased uptake into the cell
  3. Enzymatic modifications of the aminoglycoside (transposons or plasmids)
22
Q

Aminocyclitol

A

Inhibits recognition (e.g., spectinomycin)

23
Q

Spectinomycin

A
  • Inhibits recognition
  • Bacteriostatic
  • Causes the formation of unstable 70S initiation complexes (BUT DOES NOT CAUSE MISREADING AND DOES NOT INHIBIT POLYSOMAL RIBOSOMES)
24
Q

What does spectinomycin treat?

A

Exclusively for the treatment of gonorrhea caused by B-lactamase-producing gonococci or to treat gonorrhea in patients allergic to penicillins

25
Q

Tetracyclines

A
  • Inhibitors or recognition
  • Broad spectrum
  • Bacteriostatic
  • Bind to the 30S ribosomal subunit and inhibit binding of aa-tRNA to the A site
26
Q

What does tetracycline treat?

A

Chlamydia, Mycoplasma, Rickettsia (i.e., intracellular pathogens)

27
Q

Resistance to Tetracyclines

A
  1. Decreased uptake (mutations in the OmpF porin)
  2. Efflux from the bacterial cell
  3. Elongation factor-like proteins that protect the 30S ribosomal subunit
28
Q

Chloramphenicol

A
  • inhibitors of peptidyl transfer
  • broad spectrum and bacteriostatic
  • binds reversible to the 50S ribosomal subunit and alters the tRNA structure blocking peptidyl transfer
29
Q

Lincomycin and Clindamycin

A
  • inhibitors of peptidyl transfer
  • same action as chloramphenicol
  • very effective for treatment of G+ bacterial infections
30
Q

What does Clindamycin treat?

A

staphylococcal and anaerobic G- bacterial infections

31
Q

Resistance to chloramphenicol

A

plasmid-encoded acetyltransferase that catalyze the acetylation of -OH groups, which prevents 50S binding

32
Q

Resistance to clindamycin

A

Methylation of 23S ribosomal RNA which prevents drug binding to the 50S ribosomal subunit

33
Q

Macrolides

A
  • inhibitors of translocation
  • bacteriostatic
  • can treat intracellular pathogens (Mycoplasma, Legionella, Chlamydia, and Campylobacter)
34
Q

Azithromycin and Clarithromycin

A

Modified forms of Erythromycin (type of macrolide)

35
Q

Macrolide Action

A

Isn’t clear but is likely:

  1. prevent elongation
  2. prevent release of empty tRNA
  3. blockage of transpeptidation
36
Q

Macrolide Resistance

A
  1. Methylation of the 23S RNA of the 50S subunit
  2. Hydrolysis of the lactone ring by an esterase
  3. Efflux of the drug
37
Q

Ketolides

A
  • inhibitors of translocation (e.g., Telithromycin)
  • bind the exit tunnel of the large ribosomal subunit and block the exit of nascent polypeptides
  • macrolides bind to only one domain of the 50S, these can bind to two
38
Q

Streptogramins

A
  • inhibitor of translocation
  • Dalfoprisitin (binds to 50S) and Quinuprisitin (premature release of peptide chains)
  • Synercid = D + Q (alone the drugs are bacteriostatic, together they are bactericidal)

MSK Week 2 (28 decks)

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