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19 Aug 2019

What factors might decrease the pool of oxaloacetate available for the activity of the citric acid cycle? How can the pool of oxaloacetate be replenished?

Oxaloacetate is formed in the last step of the citric acid cycle by the NAD⁺-dependent oxidation of l-malate. Can a net synthesis of oxaloacetate from acetyl-CoA occur using only the enzymes and cofactors of the citric acid cycle, without depleting the intermediates of the cycle? Explain. How is oxaloacetate that is lost from the cycle (to biosynthetic reactions) replenished?

Mammalian liver can carry out gluconeogenesis using oxaloacetate as the starting material. How does this occur? Would the operation of the citric acid cycle be affected by extensive use of oxaloacetate for gluconeogenesis? Explain your answer.

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Keith LeannonLv2

21 Aug 2019

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Related questions

___ 25- The Krebs cycle begins with the union of acetyl CoA with oxaloacetate forming citrate, allowing oxidative decarboxylation reactions to occur, and ends with the conversion of malate to oxaloacetate. Using this information and your knowledge of the Krebs cycle, how many net carbons does the citric acid cycle gain?
A) 0 carbons
B) 1 carbon
C) 2 carbons
D) 4 carbons
___ 26- Directly from the Krebs cycle we can obtain:
A) ATP
B) GTP and NADPH
C) ATP and NADPH
D) ATP, GTP, and NADPH
___ 27- Which of the following is not an intermediary of the Krebs cycle?
A) oxaloacetate
B) citrate
C) succinyl CoA
D) acetyl CoA
___ 28- How many di nucleotides are reduced by four turns of the Krebs cycle?
A) 1 FADH2 and 4 NADH
B) 2 FADH2 and 8 NADH
C) 4 FADH2 and 12 NADH
D) 1 FAD and 4 NAD +

1. Choose the TWO correct statements describing the citrate cycle.

	ATP is an indirect product of the citric acid cycle
	Acetyl CoA can increase the pool of citric acid cycle intermediates
	Fatty acids can increase the pool of citric acid cycle intermediates
	ADP inhibits Î±-ketoglutarate dehydrogenase
	The pool of mitochondrial oxaloacetate can be increased by pyruvate
	All enzymes of the citric acid cycle are found soluble and free in the mitochondrial matrix

2.Which molecule in the net reaction of the citrate cycle contributes to the inhibition of pyruvate dehydrogenase?

	NADH
	H⁺
	H₂O
	FAD

3. How would a high NADH to NAD⁺ ratio be expected to affect the pyruvate dehydrogenase reaction?

	The E1 subunit is phosphorylated by pyruvate dehydrogenase kinase, and the catalytic activity of pyruvate dehydrogenase decreases.
	The last step of the pyruvate dehydrogenase reaction is blocked, resulting in a decrease in activity.
	The pyruvate dehydrogenase phosphatase-1 enzyme would increase, resulting in pyruvate dehydrogenase activation at an accelerated rate.
	The pyruvate dehydrogenase kinase enzyme activity would increase, resulting in an increase in pyruvate dehydrogenase activity.

16- When the body is deficient in oxaloacetate

a) acetyl CoA from the b-oxdiation pathway cannot enter the citric acid cycle

b) oxaloacetate is diverted to gluconeogenesis

c) acetyl CoA is diverted to form the ketone bodies

d) all of the above are true

e) none of the above

17- The synthesis of ketone bodies involves

a) synthesis of acetoacetyl-CoA by reversal of the thiolase reaction of fatty oxidation

b) synthesis of b-hydroxy-b-methylglutaryl-CoA (HMG-CoA)

c) cleavage of HMG-CoA to acetoacetate.

d) b-Hydroxybutyrate is produced by reduction of acetoacetate.

e) all of the above

18- Which of the statements about ketone body production is FALSE?

a) Ketone bodies are produced when there is more acetyl-CoA in the liver than can be oxidized in the citric acid cycle.

b) Ketone bodies production is not a normal process, and occurs only in diabetes or starvation

c) The ketone bodies produced in the body are the free acids and not the CoA esters.

d) When fatty acid oxidation in the liver is uncontrolled, ketone body production becomes excessive and life-threatening because these acidic compounds lower the pH of blood

e) When fatty acid oxidation

19- In which of the following ways can the 4-carbon compound acetoacetyl CoA produced in fatty acid degradation be further metabolized?

a) It can break down further to form acetyl CoA,

b) It can be converted to the ketone bodies

c) It can be used for synthesis of cholesterol and its many derivÂatives.

d) It can do all of the above

e) It can do none of the above

20- Acetyl CoA from the beta-oxidation pathway cannot enter the citric acid cycle in which of these circumstances?

a) periods of fasting

b) periods of starvation

c) diabetes

d) when the body is deficient in oxaloacetate