BI234 CH - MICROBIAL METABOLISM EXAM QUESTIONS
AND ANSWERS WITH COMPLETE SOLUTIONS
What role do enzymes play in metabolic pathways?
Enzymes control the chemical reactions in metabolic pathways. They are necessary for
metabolism to occur.
How is the action of a competitive inhibitor different from that of an allosteric
inhibitor?
-Competitive inhibitors have a shape that is similar to the substrate of the enzyme and
bind to the active site of the enzyme - these inhibitors compete for the active site.
-Allosteric inhibitors bind to a site other than the active site. When bound to the
allosteric site, these inhibitors induce a conformational change in the enzyme, changing
the shape of the active site and prevent the substrate from binding
Lactoferrin is a chemical in the human body that binds free iron. The absence of
iron in the body inhibits bacterial enzyme activity. Based on the information, what
role does iron play in many bacteria?
Iron is a Cofactor for bacterial enzymes
In E. coli, when tryptophan (trap) levels in the cell are high, trip binds to the
enzymes in the metabolic pathway for trp Biosynthesis. This is an example of
what type of enzyme regulation?
Feedback inhibition
,You grow a culture of E. coli in broth that contains glucose and lactose.
a) What is catabolite repression?
b) Which sugar will be used up first?
a) Catabolite repression occurs when the presence of one substrate inhibits the
metabolism of a second substrate. Cells use the more energy efficient (energetic
favorable) source first.
b) Glucose
The end pathways of fermentation, aerobic respiration and anaerobic respiration
oxidize NADH to NAD+. Why is this recycling of NAD+ important?
-NAD+ is required Coenzyme for the enzymes in Glycolysis and the Krebs cycle.
-Without NAD+, these metabolic pathways would not run. NADH must be oxidized to
NAD+ so that metabolism can continue.
How many molecules of ATP are produced per molecule of glucose by aerobic
respiration, anaerobic respiration and fermentation?
-Aerobic respiration - 34-36 ATP
-Anaerobic respiration - up to 32 ATP
-Fermentation - up to 2 ATP
What are the final electron acceptors used by by aerobic respiration, anaerobic
respiration and fermentation?
, -Aerobic respiration - Oxygen
-Anaerobic respiration - Inorganic oxygen containing molecule
-Fermentation - Organic molecule (pyruvate)
Consider two flasks of the same facultative anaerobe grown in broth
supplemented with glucose for 16hrs. One flask is incubated in the presence of
Oxygen, the other in incubated under anaerobic conditions. If all other conditions
are held constant, what differences would you predict for the cell masses of the
two cultures.
-The culture grown in aerobic conditions would have a greater cell mass. In the
presence of oxygen, more ATP will be produces per glucose, allowing for a faster
growth rate than in the culture grown under anaerobic conditions.
How does oxidation of a molecule occur without molecular oxygen?
Oxidation - is the Loss of electrons; molecular oxygen is not necessary for this to occur.
What are the end product for each kind of Fermentation:
a) Homolactic fermentation
b) Heterolactic fermentation
c) Propionic acid fermentation
d) Mixed acid fermentation
e) 2,3-Butanediol fermentation
f) ABE fermentation
a) Homolactic fermentation- Lactic acid (yogurt, kefir, beer, bread)
AND ANSWERS WITH COMPLETE SOLUTIONS
What role do enzymes play in metabolic pathways?
Enzymes control the chemical reactions in metabolic pathways. They are necessary for
metabolism to occur.
How is the action of a competitive inhibitor different from that of an allosteric
inhibitor?
-Competitive inhibitors have a shape that is similar to the substrate of the enzyme and
bind to the active site of the enzyme - these inhibitors compete for the active site.
-Allosteric inhibitors bind to a site other than the active site. When bound to the
allosteric site, these inhibitors induce a conformational change in the enzyme, changing
the shape of the active site and prevent the substrate from binding
Lactoferrin is a chemical in the human body that binds free iron. The absence of
iron in the body inhibits bacterial enzyme activity. Based on the information, what
role does iron play in many bacteria?
Iron is a Cofactor for bacterial enzymes
In E. coli, when tryptophan (trap) levels in the cell are high, trip binds to the
enzymes in the metabolic pathway for trp Biosynthesis. This is an example of
what type of enzyme regulation?
Feedback inhibition
,You grow a culture of E. coli in broth that contains glucose and lactose.
a) What is catabolite repression?
b) Which sugar will be used up first?
a) Catabolite repression occurs when the presence of one substrate inhibits the
metabolism of a second substrate. Cells use the more energy efficient (energetic
favorable) source first.
b) Glucose
The end pathways of fermentation, aerobic respiration and anaerobic respiration
oxidize NADH to NAD+. Why is this recycling of NAD+ important?
-NAD+ is required Coenzyme for the enzymes in Glycolysis and the Krebs cycle.
-Without NAD+, these metabolic pathways would not run. NADH must be oxidized to
NAD+ so that metabolism can continue.
How many molecules of ATP are produced per molecule of glucose by aerobic
respiration, anaerobic respiration and fermentation?
-Aerobic respiration - 34-36 ATP
-Anaerobic respiration - up to 32 ATP
-Fermentation - up to 2 ATP
What are the final electron acceptors used by by aerobic respiration, anaerobic
respiration and fermentation?
, -Aerobic respiration - Oxygen
-Anaerobic respiration - Inorganic oxygen containing molecule
-Fermentation - Organic molecule (pyruvate)
Consider two flasks of the same facultative anaerobe grown in broth
supplemented with glucose for 16hrs. One flask is incubated in the presence of
Oxygen, the other in incubated under anaerobic conditions. If all other conditions
are held constant, what differences would you predict for the cell masses of the
two cultures.
-The culture grown in aerobic conditions would have a greater cell mass. In the
presence of oxygen, more ATP will be produces per glucose, allowing for a faster
growth rate than in the culture grown under anaerobic conditions.
How does oxidation of a molecule occur without molecular oxygen?
Oxidation - is the Loss of electrons; molecular oxygen is not necessary for this to occur.
What are the end product for each kind of Fermentation:
a) Homolactic fermentation
b) Heterolactic fermentation
c) Propionic acid fermentation
d) Mixed acid fermentation
e) 2,3-Butanediol fermentation
f) ABE fermentation
a) Homolactic fermentation- Lactic acid (yogurt, kefir, beer, bread)
