BIOC3022 EXAM 4 COMPLETE QUESTIONS
WITH 100% CORRECT ANSWERS
\.What enzyme cleaves citrate in the cytoplasm during fatty acid
synthesis? - ANSWERS-ATP-Citrate Lyase
\.What two molecules are produced when ATP-Citrate Lyase cleaves
citrate? - ANSWERS-Oxaloacetate and acetyl-CoA
\.What is the first committed step of fatty acid synthesis? - ANSWERS-
Carboxylation of acetyl-CoA to form malonyl-CoA by acetyl-CoA
carboxylase (ACC)
\.What cofactors/energy does the ACC reaction require? - ANSWERS-
ATP and biotin
\.What is the role of Fatty Acid Synthase (FAS)? - ANSWERS-It is a multi-
enzyme protein complex that catalyzes the addition of two-carbon units
to a growing acyl chain
,\.How does chain extension occur in FAS? - ANSWERS-Malonyl-CoA is
decarboxylated, and the resulting two-carbon fragment is added to the
growing chain
\.What is the final product of FAS-mediated chain extension? -
ANSWERS-Palmitic acid (16 carbons)
\.What happens if a fatty acid longer than 16 carbons or with double
bonds is needed? - ANSWERS-Other enzymes (elongases and
desaturases) add further carbons and double bonds
\.What metabolic condition triggers the initiation of fatty acid synthesis?
- ANSWERS-A high energy charge, causing NADH accumulation
\.What happens to citrate when the energy charge is high? - ANSWERS-
Citrate accumulates in the TCA cycle and is transported to the cytosol
\.Why does citrate accumulate when glycolysis is high? - ANSWERS-
Excess acetyl-CoA enters the TCA cycle; when NADH builds up and slows
the cycle, citrate backs up and is exported
\.How does citrate cross the inner mitochondrial membrane? -
ANSWERS-Via the citrate transport protein (a specific carrier)
,\.How does citrate cross the outer mitochondrial membrane? -
ANSWERS-By free diffusion
\.What does ATP-citrate lyase do to citrate in the cytosol? - ANSWERS-It
cleaves citrate into acetyl-CoA and oxaloacetate, consuming ATP
\.What happens to oxaloacetate (OAA) after citrate is cleaved in the
cytosol? - ANSWERS-OAA is reduced to malate by malate
dehydrogenase, using NADH
\.What enzyme converts malate to pyruvate in the cytosol? - ANSWERS-
Malate enzyme (malic enzyme)
\.What cofactor does malic enzyme require, and what is produced? -
ANSWERS-It requires NADP⁺ and produces NADPH and CO₂
\.Why is the NADPH generated by malic enzyme significant? -
ANSWERS-It is required for lipid synthesis (though it is a minor pathway
for NADPH production)
\.What happens to pyruvate produced by malic enzyme? - ANSWERS-It
is transported back into the mitochondria and converted back to OAA
by pyruvate carboxylase
, \.What is the function of the carboxybiotin group in ACC? - ANSWERS-It
transfers a carboxylate group to acetyl-CoA to form malonyl-CoA
\.What is malonyl-CoA's role in fatty acid synthesis? - ANSWERS-It is the
donor of two-carbon acetyl units for chain elongation
\.How does malonyl-CoA inhibit fatty acid oxidation? - ANSWERS-High
levels of malonyl-CoA inhibit fatty acid transport into the mitochondria,
acting as a critical negative regulator of β-oxidation
\.What is ACC's role in fatty acid synthesis? - ANSWERS-It is the key,
rate-limiting regulated enzyme that controls the rate of fatty acid
synthesis
\.What are the two main regulatory mechanisms of ACC? - ANSWERS-
(1) Allosteric regulation and (2) phosphorylation by AMP-activated
protein kinase (AMPK)
\.What allosteric activator stimulates ACC? What allosteric inhibitor
inactivates ACC? - ANSWERS-Citrate; Palmitoyl-CoA (the end product)
\.What activates AMPK? - ANSWERS-High AMP/ATP ratio (low energy
state)
WITH 100% CORRECT ANSWERS
\.What enzyme cleaves citrate in the cytoplasm during fatty acid
synthesis? - ANSWERS-ATP-Citrate Lyase
\.What two molecules are produced when ATP-Citrate Lyase cleaves
citrate? - ANSWERS-Oxaloacetate and acetyl-CoA
\.What is the first committed step of fatty acid synthesis? - ANSWERS-
Carboxylation of acetyl-CoA to form malonyl-CoA by acetyl-CoA
carboxylase (ACC)
\.What cofactors/energy does the ACC reaction require? - ANSWERS-
ATP and biotin
\.What is the role of Fatty Acid Synthase (FAS)? - ANSWERS-It is a multi-
enzyme protein complex that catalyzes the addition of two-carbon units
to a growing acyl chain
,\.How does chain extension occur in FAS? - ANSWERS-Malonyl-CoA is
decarboxylated, and the resulting two-carbon fragment is added to the
growing chain
\.What is the final product of FAS-mediated chain extension? -
ANSWERS-Palmitic acid (16 carbons)
\.What happens if a fatty acid longer than 16 carbons or with double
bonds is needed? - ANSWERS-Other enzymes (elongases and
desaturases) add further carbons and double bonds
\.What metabolic condition triggers the initiation of fatty acid synthesis?
- ANSWERS-A high energy charge, causing NADH accumulation
\.What happens to citrate when the energy charge is high? - ANSWERS-
Citrate accumulates in the TCA cycle and is transported to the cytosol
\.Why does citrate accumulate when glycolysis is high? - ANSWERS-
Excess acetyl-CoA enters the TCA cycle; when NADH builds up and slows
the cycle, citrate backs up and is exported
\.How does citrate cross the inner mitochondrial membrane? -
ANSWERS-Via the citrate transport protein (a specific carrier)
,\.How does citrate cross the outer mitochondrial membrane? -
ANSWERS-By free diffusion
\.What does ATP-citrate lyase do to citrate in the cytosol? - ANSWERS-It
cleaves citrate into acetyl-CoA and oxaloacetate, consuming ATP
\.What happens to oxaloacetate (OAA) after citrate is cleaved in the
cytosol? - ANSWERS-OAA is reduced to malate by malate
dehydrogenase, using NADH
\.What enzyme converts malate to pyruvate in the cytosol? - ANSWERS-
Malate enzyme (malic enzyme)
\.What cofactor does malic enzyme require, and what is produced? -
ANSWERS-It requires NADP⁺ and produces NADPH and CO₂
\.Why is the NADPH generated by malic enzyme significant? -
ANSWERS-It is required for lipid synthesis (though it is a minor pathway
for NADPH production)
\.What happens to pyruvate produced by malic enzyme? - ANSWERS-It
is transported back into the mitochondria and converted back to OAA
by pyruvate carboxylase
, \.What is the function of the carboxybiotin group in ACC? - ANSWERS-It
transfers a carboxylate group to acetyl-CoA to form malonyl-CoA
\.What is malonyl-CoA's role in fatty acid synthesis? - ANSWERS-It is the
donor of two-carbon acetyl units for chain elongation
\.How does malonyl-CoA inhibit fatty acid oxidation? - ANSWERS-High
levels of malonyl-CoA inhibit fatty acid transport into the mitochondria,
acting as a critical negative regulator of β-oxidation
\.What is ACC's role in fatty acid synthesis? - ANSWERS-It is the key,
rate-limiting regulated enzyme that controls the rate of fatty acid
synthesis
\.What are the two main regulatory mechanisms of ACC? - ANSWERS-
(1) Allosteric regulation and (2) phosphorylation by AMP-activated
protein kinase (AMPK)
\.What allosteric activator stimulates ACC? What allosteric inhibitor
inactivates ACC? - ANSWERS-Citrate; Palmitoyl-CoA (the end product)
\.What activates AMPK? - ANSWERS-High AMP/ATP ratio (low energy
state)
