Exam #1: Microbial Metabolism Flashcards
What is the lag phase?
Initial period where the bacteria accumulates metabolites for maximal growth, but:
- No cell division occurs
- Sensitive to antimicrobials
What is the exponential phase?
Bacteria rapidly multiply by binary fission i.e. population doubles at constant rate
- Most susceptible to antimicrobials
What is the stationary phase?
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
What is the decline phase?
Terminal phase where more bacteria are killed than generated
What are the minimum requirements for growth?
- Carbon source
- Nitrogen source
- Energy
- Water
- Ions
What is an Obligate aerobe?
A bacteria that requires oxygen & metabolize by respiration
Produce catalase & superoxide dismutase
What is an Obligate anaerobe?
A bacteria inhibited or killed by oxygen & utilizes fermentation for respiration
(Do NOT produce catalase & superoxide dismutase)
Which is more efficient, respiration or fermentation?
Respiration
What is a Facultative anaerobe?
Bacteria that grow under aerobic or anaerobic conditions
Produce catalase but NOT superoxide dismutase i.e. cannot handle superoxide anion
Define Microaerophilic.
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)
What is the function of superoxide dismutase & catalase?
Enzymes that generally function to counteract ROS
What is the reaction carried out by superoxide dismutase?
Superoxide dismutase= counteracts superoxide anion by breaking it down into hydrogen peroxide & molecular oxygen
What is the reaction carried out by catalase?
Catalase= counteracts hydrogen peroxide by breaking it down into water & molecular oxygen
Which type of bacteria express superoxide dismutase/ catalase & which do not?
Aerobic bacteria express superoxide dismutase & catalase; aNaerobic do NOT
What is the ultimate electron receptor in aerobic respiration?
Molecular oxygen
What is the ultimate electron receptor in anaerobic respiration?
Compounds other than oxygen e.g. nitrate & sulfate
What can be measured from the fermentation process for diagnostic purposes?
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.
How is nucleic acid synthesis used as a target for antibiotics?
- 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
How is DNA replication used as a target for antibiotics?
Quinolones target bacterial DNA gyrase (required for winding & unwinding DNA)
How are transcription & translation used as a target for antibiotics?
- 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
What is folate derived from in bacteria? How does this compare to humans?
In bacteria, folate is derived from para-aminobenzoic acid (PABA)
What are antifolates?
Drugs that inhibit folate synthesis i.e. bacterial purine & thymidine synthesis.
What two drugs are categorized as antifolates? What are their drug targets?
1) Sulfonamides= Dihydropteroate synthase (DHPS) inhibitors
2) DHFR Inhibitors= Dihydrofolate reductase (DHFR) inhibitors
List the 8 steps of Peptidoglycan synthesis.
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
What are transglycosylases?
Enzymes that added NAG-NAM-pentapeptide to the growing peptidoglycan chain
What is transpeptidation?
Reaction that connects adjacent NAG-NAM-pentapeptides in the peptidoglycan chain via the pentapeptides
What are transpeptidases or PBPs?
Enzymes that carry out the transpeptiation reaction, also called Penecillin Binding Proteins (PBPs) because they bind PCN
Where in the pentapeptide does the transpeptidation reaction occur?
Between the 3rd & 4th amino acid positions
- Free amine of the diamino acid in position 3
- D-alanine in position 4 of adjacent chain
Describe the mechanism of Vancomycin.
Vancomycin inhibits the transglycosylation reaction, preventing the addition of NAG-NAM-pentapeptide to the growing peptidoglycan chain.
Describe the mechanism of Bacitracin.
Bacitracin inhibits Bactoprenol from being recycled i.e. NAG-NAM-pentapeptide-bactoprenol cannot be transported across the cell membrane.
Describe the mechanism of B-Lactams.
B-Lactams are the overarching class of antibiotics that penecillin falls into; they inhibit the transpeptidation reaction.
During what phase will spore forming bacteria undergo sporulation? What type of bacteria form spores?
- Stationary phase
- Gram (+)
