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bacteriology > antibiotics > Flashcards

antibiotics Flashcards

1
Q

mechanisms

A 
interfere with critical process or structure:
substrate analogues 
steric hindrance 
enzymatic inactivation
disruption or subversion
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2
Q

selective toxicity recurring themes

A

agent doesnt get into mammalial cells
targets processes/enzymes not in mammalial cells or are different
agent is pro drug only active in bacteria

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3
Q

interfere with nucleotide biosynthesis

A

sulphonamides

trimethoprim

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4
Q

interfere with RNA transcription

A

Rifamycin binds RNA polymerase

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5
Q

target protein synthesis

A 
linezolid
fuscidic acid (not ribosomes)
macrolides 
tetracyclines 
aminoglycosides
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6
Q

target cell wall synthesis

A

b lactams
cycloserine
glycopeptides

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7
Q

target tropo-isomerases

A

quinolones

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8
Q

target cytoplasmic membrane intergrity

A

polymyxins

daptomycin

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9
Q

peptidoglycan structure and function

A

crystal lattice structure
glycan polymers of alternating NAG and NAM monomers.
peptide bridges cross link the strands
provides protection against osmotic pressure

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10
Q

peptidoglycan biosynthesis final 2 steps

A

pentapeptide is used for cross linking reaction which has 2 D-ala-D-ala amino acids (resistant to proteolytic attack)
transglycosylation involves polymerization of the disaccharide with glycan strands
transpeptidation involves cross linking with pentapeptides

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11
Q

penicillin binding proteins

A

catalyse transglycosylation and transpeptidation

tethered in cytoplasmic membrane

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12
Q

2 antibiotic classes tht target cell wall biosynthesis

A

b lactams:
penicillins, cephalocporins.
glycopeptides
vancomycin, teicoplanin

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13
Q

penicillin

A

has a D-alanyl-Dalanine in the B lactam ring - so bind Penicllin Binding Proteins (analogue to natural substrate)
inactivates the enzyme - binds the serine residue which causes nucleophillic attack on the ring, opening it up and it becomes contently attached to active site serine - enzyme no longer active
transpeptidation blocked - cell wall loses integrity

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14
Q

peptidoglycan hydrolases

A

bacterial enzymes
break bonds within peptidoglycan at the division site. Not inhibited by b lactams
breaks down cell wall
osmotic lysis

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15
Q

vancomycin

A

binds D-ala D-ala of peptidoglycan precursor
forms hydrogen bond network - binds to precursor to occludes it and prevents it being used as a substrate for PBP.
prevents transglycosylation (not incorporated into glycan strands) and transpeptidation
narrow spectrum - only active against gram positive
cannot get through outer membrane porin (1500 daltons), so cannot access peptidoglycan in gram negative

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16
Q

Cycloserine

A

competitive inhibitor of enzymes that synthesise and ligate the D-alanines

17
Q

selective toxicity of beta lactams

A

mammalians dont have PBPs or cell walls

18
Q

daptomycin

A

gram positives membrane integrity disruption
cyclical head group and lipophilic tail
lipophilic tail inserts into membrane
reliance on calcium ions to reduce repulsion by negative charge of head group and cell membrane
aggregate
physical disruption of membrane
membrane depolarization and leakage of content

19
Q

polymycin B and E

A

specific for gram negatives
make contact with LPS
translocated through outer membrane
toxic

20
Q

selective toxicity of daptomycin

A

different membrane compositions of mammalian and bacterial

21
Q

sulfonamides

often used with trimethoprim = co-trimoxozole = synergism

A

target nucleotide metabolism
synthetic
target tetrahydrofolate biosynthesis pathway, generates dTMP - precursor for DNA synthesis
inhibit GTP -> dyhyropteroate. analogous to PABA substrate for DHPs. enzyme binds to sulfonamides and produces a dead-end complex
uses up enzyme , waste resources

22
Q

Trimethoprim

A

competitive inhibitor
(analogue of dihydrofolate acid)
binds dihydrofolate reductase
higher affinity for bacterial enzyme than mammalian

23
Q

sulfonamide selective toxicity

A

humans obtain intermediates from diet - dont undergo pathway

24
Q

quinolones

A

interfere with nucleotide biosynthesis, block DNA synthesis
act on 2 enzymes - topoisomerases DNA gyrase and DNA tropoisomerase 4
both catalyse ATP dependent DNA double strand break/rejoining reactions, achieves super coiling
quinolones similar to bases - base stacking interactions, binds quinolone binding pocket
enzyme cannot resolve structure - double strand breaks accumulate
DNA synthesis shuts down, cell death

25
Q

quinolones selective toxicity

A

Mammalians dont have DNA gyrase

quonolones affinity for bacterial troposimerase higher

26
Q

Rifampycin

A

only inhibitor that targets transcription
target is RNA polymerase
binds beta subunit of prokaryotic RNA pol.
occludes the exit tunnel
causes abortive initiation of transcription, DNA cannot pass through

27
Q

rifampycin selective toxicity

A

prokaryotic RNA pol is structurally different to mammalian

28
Q

targeting protein synthesis

A

mostly bind ribosomes
mostly bacteriostatic
mostly interfere with elongation step

29
Q

selective toxicity of protein synthesis inhibitors

A

selective toxicity comes from the difference between prokaryotic and eukaryotic ribosomes
prokaryotic - 70S made up of 50S and 30S subunits
eukaryotic - 80S made up of 40S and 80S

30
Q

mupirocin

A

inhibits formation of isoleucyl tRNA - interferes with charging
8000 times more affinity for bacterial

31
Q

linezolid

A

binds to the A site of the 50s ribosome
prevents attachment of incoming amino acyl tRNA
used for MRSA infection

32
Q

macrolides

A

natural product but modified
azithromycin has expanded spectrum -used in respiratory infection and chlamydial infection
binds to the 23s rRNA peptide exit site in the 50S subunit, blocks peptide leaving
causes premature termination

33
Q

fusidic acid

A

binds to Elongation Factor G (EF-G)
EF-G allows translocation of mRNA through ribosome.
binding of fusidic acid binds EF-G, cannot dissociate from ribosome acceptor site, materials cannot be delivered to ribosome

34
Q

selective toxicity

A

preferentially accumulates inside bacterial cells

bacteriology (14 decks)

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