Week 14.1 Antimicrobials

Question 1

What things are used to to kill bacteria or inhibit their growth?

Answer 1

antibiotics and disinfectants

Question 2

Examples of antibiotics and disinfectants

Answer 2

-Penicillin prevents bacteria from building a cell wall (block peptidoglycan)
-Chloramphenicol and tetracycline inhibit protein synthesis
-Rifampicin inhibits RNA transcription
-Alcohol dissolves bacterial membrane

Question 3

Why don’t antibiotics or disinfectants kill us like they do bacteria?

Answer 3

We have slight structure differences in ribosomes so they don’t target our cells

Question 4

Antibiotics bind to…

Answer 4

proteins

Question 5

Competitive inhibition vs noncompetitive inhibition

Answer 5

-Competitive: competitive inhibitor and substrate compete for active site
-Noncompetitive: competitive inhibitor binds to allosteric site that induces a conformational change in the active site, preventing the substrate from binding to it

Question 6

Bacteriostatic

Answer 6

the growth of the bacteria is inhibited but the bacteria are not necessarily killed

Question 7

Bactericidal

Answer 7

the bacteria are killed

Question 8

Six primary antibiotic targets in bacteria

Answer 8

1. Cell membrane
2. Cell wall synthesis
3. DNA replication
4. RNA synthesis
5. Protein synthesis
6. Metabolism (folic acid synthesis)

Question 9

Other special antibiotic targets in bacteria

Answer 9

1. Biofilm formation
2. Flagella/pilli
3. Quorum sensing

Question 10

What do you need to know to predict how an antibiotic will affect a cell?

Answer 10

1. Antibiotic’s target
2. Target’s function

Question 11

What is the bacterial plasma membrane?

Answer 11

A phospholipid bilayer with a variety of embedded proteins, lipids, and carbohydrates that perform various functions for the cell

Question 12

Functions of embedded proteins

Answer 12

1. Transport
2. Enzymatic activity
3. Signal transduction
4. Cell-cell recognition
5. Intracellular joining
6. Attachment to the cytoskeleton and ECM

Question 13

Antibiotics that disrupt the bacterial membrane

Answer 13

1. Daptomycin: causes depolarization of cytoplasmic membrane, resulting in disruption of ionic concentration gradients
2. Bacitracin: inhibits export of peptidoglycan precursors
3. Polymyxins: disrupts the membrane

Question 14

Isotonic solution

Answer 14

no net movement of water particles; cell membrane is attached to cell wall

Question 15

Hypertonic solution

Answer 15

water particles move OUT of the cell; cell membrane shrinks and detaches from cell wall (plasmolysis)

Question 16

Hypotonic solution

Answer 16

water particles move INTO the cell; cell wall counteracts osmotic pressure to prevent swelling and lysis

Question 17

Peptidoglycan

Answer 17

a polymer composed of alternating N-acetylmuramic acid (NAM) and N-acetylglucosamine (NAG)
-NAM: peptide sidechain
-NAG: does not have peptide sidechain

Question 18

NAG-NAM synthesis

Answer 18

1. NAM is synthesized in the cytoplasm and linked to UDP
2. NAM is linked to bactoprenol
3. NAG is added to NAM
4. Bactoprenol flips NAM-NAG to periplasm
5. Transpeptidase polymerizes the disaccharides into the growing peptidoglycan chain (crosslinking occurs)
6. Bactoprenol flips back to cytoplasm

Question 19

Why are peptide chains on 2 stacked N-acetylmuramic acids crosslinked?

Answer 19

to stabilize the layers

Question 20

What is separation of bacterial daughter cells controlled by?

Answer 20

FtsZ protein

Question 21

How do bacterial cells divide using FtsZ protein?

Answer 21

FtsZ proteins assembled along the membrane and form the Z ring. Then the Z ring is anchored to the membrane and pinches together to cleave the cells.

Question 22

How do bacterial cells with cell walls divide?

Answer 22

Autolysins (an enzyme) cleave peptidoglycan so the dividing cell can separate
-Ex: amidase

Question 23

What happens when autolysins cleave the cell wall?

Answer 23

New peptidoglycan is inserted along the break to facilitate elongation and septum formation

Question 24

Antibiotics that affect cell wall synthesis

Answer 24

1. Beta-lacams
2. Beta-lacam/B-lactamase inhibitors
3. Vancomycin
4. Bacitracin
5. Isoniazid/ethionamide
6. Ethambutol
7. Cycloserine

Question 25

Beta-lacams

Answer 25

-Penicillins, cephalosporins, cephamycins, carbapenems, monobactams -Mechanism: Bind proteins and enzymes responsible for peptidoglycan synthesis

Question 26

Beta-lacam/beta-lactamase inhibitors

Answer 26

Bind beta-lactamases and prevent INactivation of lactam

Question 27

Vancomycin

Answer 27

Inhibits cross-linkage of peptidoglycan layers

Question 28

Bacitracin

Answer 28

Inhibits export of peptidoglycan precursors

Question 29

Isoniazid/ethionamide

Answer 29

Inhibit mycolic acid synthesis (mycobacterium)

Question 30

Ethambutol

Answer 30

Inhibits arabinogalactan synthesis (mycobacterium)

Question 31

Cycloserine

Answer 31

Inhibits cross-linkage of peptidoglycan layers

Question 32

Central Dogma of Molecular Biology

Answer 32

DNA > RNA > protein

Question 33

DNA replication (summarized)

Answer 33

1. Complementary strands of DNA must be separated and prevented from rewinding (DNA gyrase, helicase, single-stranded binding proteins) 2. DNA polymerase requires an RNA primer to bind to DNA (RNA primase) 3. Discontinuous strands must be ligated together (Okazaki fragments and DNA ligase)

Question 34

DNA gyrase

Answer 34

relaxes supercoiling

Question 35

Helicase

Answer 35

separates strands of DNA

Question 36

Single-stranded binding proteins

Answer 36

prevent DNA from coming back together

Question 37

RNA primase

Answer 37

adds complementary RNA nucleotides to DNA -allows attachment of DNA polymerase -problem: RNA nucleotides instead of DNA

Question 38

Okazaki fragments

Answer 38

short sequences of DNA that are synthesized discontinuously

Question 39

DNA ligase

Answer 39

joins the 5' phosphate to the 3' end hydroxyl

Question 40

Antibiotics that disrupt DNA replication

Answer 40

1. Quinolones 2. Metronidazole

Question 41

Quinolones

Answer 41

-nalidixic acid, ciprofloxacin, levofloxacin, moxifloxacin -Mechanism: inhibits DNA gyrase (strands remain extremely supercoiled)

Question 42

Metronidazole

Answer 42

Disrupts host DNA and therefore DNA replication

Question 43

RNA polymerase

Answer 43

able to bind DNA, unwind, unzip, and polymerize without help from other enzymes

Question 44

Antibiotics that disrupt RNA synthesis

Answer 44

1. Rifampin (rifampicin): inhibits RNA polymerase 2. Rifabutin: inhibits RNA polymerase *bacteriostatic

Question 45

Antibiotics that disrupt protein synthesis

Answer 45

1. Aminoglycosides 2. Tetracyclines 3. Glycylclines 4. Oxazolidinone 5. Macrolides, ketolides, clindamycin, streptogramins

Question 46

Aminoglycosides

Answer 46

-streptomycin, kanamycin, gentamycin, tobramycin, amikacin -Mechanism: produce premature release from 30S ribosomal subunit

Question 47

Tetracyclines

Answer 47

Prevent peptide elongation at 30S ribosomal subunit

Question 48

Glycyclines

Answer 48

Bind to 30S ribosomal subunit (prevent 50S from binding)

Question 49

Oxazolidinone

Answer 49

Prevents initiation of protein synthesis at 50S ribosomal subunit

Question 50

Macrolides, ketolides, clindamycin, streptogramins

Answer 50

Prevent polypeptide elongation at 50S ribosome

Question 51

Why is folic acid important for protein and nucleic acid synthesis?

Answer 51

It's a required precursor

Question 52

Why is folic acid synthesis not a good target?

Answer 52

-bacterial cells can become persister cells -bacterial cells can also get folic acid from nearby

Question 53

Antibiotics that disrupt folic acid synthesis (aka antimetabolites)

Answer 53

1. Sulfonamides: inhibit dihydropteroate synthesis and disrupt folic acid synthesis 2. Dapsone: inhibits dihydropteroate synthase 3. Trimethoprim: inhibits dihydrofolate reductase and disrupts folic acid synthesis