Exam #1: Microbial Metabolism

Question 1

What is the lag phase?

Answer 1

Initial period where the bacteria accumulates metabolites for maximal growth, but:

• No cell division occurs
• Sensitive to antimicrobials

Question 2

What is the exponential phase?

Answer 2

Bacteria rapidly multiply by binary fission i.e. population doubles at constant rate
- Most susceptible to antimicrobials

Question 3

What is the stationary phase?

Answer 3

Phase where nutrients are depleted & toxic waste products accumulate BUT cell population remains constant (no dying yet)
- Spore forming (gram-positive) bacteria will enter spore phase during this time

Question 4

What is the decline phase?

Answer 4

Terminal phase where more bacteria are killed than generated

Question 5

What are the minimum requirements for growth?

Answer 5

• Carbon source
• Nitrogen source
• Energy
• Water
• Ions

Question 6

What is an Obligate aerobe?

Answer 6

A bacteria that requires oxygen & metabolize by respiration

(Produce catalase & superoxide dismutase)

Question 7

What is an Obligate anaerobe?

Answer 7

A bacteria inhibited or killed by oxygen & utilizes fermentation for respiration

(Do NOT produce catalase & superoxide dismutase)

Question 8

Which is more efficient, respiration or fermentation?

Answer 8

Respiration

Question 9

What is a Facultative anaerobe?

Answer 9

Bacteria that grow under aerobic or anaerobic conditions

Produce catalase but NOT superoxide dismutase i.e. cannot handle superoxide anion

Question 10

Define Microaerophilic.

Answer 10

A microaerophillic bacteria requires 5-10% oxygen for maximal growth i.e. grow best at low O2 concentrations

(Produce small amounts of catalase, but NOT superoxide dismutase)

Question 11

What is the function of superoxide dismutase & catalase?

Answer 11

Enzymes that generally function to counteract ROS

Question 12

What is the reaction carried out by superoxide dismutase?

Answer 12

Superoxide dismutase= counteracts superoxide anion by breaking it down into hydrogen peroxide & molecular oxygen

Question 13

What is the reaction carried out by catalase?

Answer 13

Catalase= counteracts hydrogen peroxide by breaking it down into water & molecular oxygen

Question 14

Which type of bacteria express superoxide dismutase/ catalase & which do not?

Answer 14

Aerobic bacteria express superoxide dismutase & catalase; aNaerobic do NOT

Question 15

What is the ultimate electron receptor in aerobic respiration?

Answer 15

Molecular oxygen

Question 16

What is the ultimate electron receptor in anaerobic respiration?

Answer 16

Compounds other than oxygen e.g. nitrate & sulfate

Question 17

What can be measured from the fermentation process for diagnostic purposes?

Answer 17

Obligate anaerobes convert pyruvate into various end-products through the fermentation process; these bacteria can be identified on the basis of these different end-products.

Question 18

How is nucleic acid synthesis used as a target for antibiotics?

Answer 18

• Bacteria must synthesize folate for purine & thymidine synthesis
• Enzymes in this synthesis process are drug-targets
• Humans obtain folate from diet & are not harmed by these drugs

Question 19

How is DNA replication used as a target for antibiotics?

Answer 19

Quinolones target bacterial DNA gyrase (required for winding & unwinding DNA)

Question 20

How are transcription & translation used as a target for antibiotics?

Answer 20

• Both occur simultaneously in bacteria (no nuclear membrane)
• Rifampin inhibits bacterial DNA-dependent RNA polymerase
• Bacteria= 70S ribosome, which is different from human ribosome & a drug target

Question 21

What is folate derived from in bacteria? How does this compare to humans?

Answer 21

In bacteria, folate is derived from para-aminobenzoic acid (PABA)

Question 22

What are antifolates?

Answer 22

Drugs that inhibit folate synthesis i.e. bacterial purine & thymidine synthesis.

Question 23

What two drugs are categorized as antifolates? What are their drug targets?

Answer 23

1) Sulfonamides= Dihydropteroate synthase (DHPS) inhibitors

2) DHFR Inhibitors= Dihydrofolate reductase (DHFR) inhibitors

Question 24

List the 8 steps of Peptidoglycan synthesis.

Answer 24

1) Activation of NAG & NAM in cytoplasm to make UDP-NAG & UDP-NAM
2) Pentapeptide added to UDP-NAM to make UDP-NAM-pentapeptide
3) UDP-NAM-pentapeptide added to bactroprenol on the inner leaflet of the cell membrane
4) NAG added to UDP-NAM-pentapeptide-bactoprenol
5) NAG-NAM-pentapeptide-bactoprenol transported across membrane to outer leaflet
6) NAG-NAM-pentapeptide added to growing peptidoglycan chain by transglycosylases
7) Bactoprenol recycled
8) Transpeptidation

Question 25

What are transglycosylases?

Answer 25

Enzymes that added NAG-NAM-pentapeptide to the growing peptidoglycan chain

Question 26

What is transpeptidation?

Answer 26

Reaction that connects adjacent NAG-NAM-pentapeptides in the peptidoglycan chain via the pentapeptides

Question 27

What are transpeptidases or PBPs?

Answer 27

Enzymes that carry out the transpeptiation reaction, also called Penecillin Binding Proteins (PBPs) because they bind PCN

Question 28

Where in the pentapeptide does the transpeptidation reaction occur?

Answer 28

Between the 3rd & 4th amino acid positions - Free amine of the diamino acid in position 3 - D-alanine in position 4 of adjacent chain

Question 29

Describe the mechanism of Vancomycin.

Answer 29

Vancomycin inhibits the transglycosylation reaction, preventing the addition of NAG-NAM-pentapeptide to the growing peptidoglycan chain.

Question 30

Describe the mechanism of Bacitracin.

Answer 30

Bacitracin inhibits Bactoprenol from being recycled i.e. NAG-NAM-pentapeptide-bactoprenol cannot be transported across the cell membrane.

Question 31

Describe the mechanism of B-Lactams.

Answer 31

B-Lactams are the overarching class of antibiotics that penecillin falls into; they inhibit the transpeptidation reaction.

Question 32

During what phase will spore forming bacteria undergo sporulation? What type of bacteria form spores?

Answer 32

- Stationary phase | - Gram (+)