Answers for Biochemistry II, Test Two (April 2, 2001)
(100 points total; 20 points for each question.)
Name:
; Student Number:
1. In order to examine the citric acid cycle you have obtained a pure preparation of
isolated, intact mitochondria. You add some succinyl-CoA to the suspension of
mitochondria. How many moles of ATP would you expect to be generated in one
turn of the citric acid cycle from each mole of succinyl-CoA added to the test tube?
Answer:
E (succinyl-CoA can not enter the intact mitochondrion)
(a) 3
(b) 4
(c) 5
(d) 5.5
(e) No ATP would form under these conditions.
2. All of the following enzymes are linked to the reduction of NADH except:
Answer: C
A. Isocitrate dehydrogenase.
B. Lactate dehydrogenase.
C. Succinate dehydrogenase.
D. Pyruvate dehydrogenase.
E. -ketoglutarate drhydrogenase.
3. Indicate whether each of the following statements about the glyoxylate cycle is true
(T) or false (F).
A. It allows the products of fatty acid oxidation to be converted, eventually, to
glucose. T
B.
It provides intermediates for the citric acid cycle during periods when
amino acids are being synthesized. T
C. It depletes cellular stores of oxaloacetate. F
D. It occurs instead of the citric acid cycle in plants. F
4. Place the following steps in lipid oxidation in their proper sequence. (Note: this is
not a complete list of steps.) Answer: D, E, B, F, C,A
A. Thiolysis.
B. Reaction of fatty acyl-CoA with carnitine.
C. Oxidation requiring NAD+.
D. Hydrolysis of triacylglycerol by lipase.
E. Activation of fatty acid by joining to CoA.
F. Hydration.
5. How does the production of ketone bodies allow continued oxidation of fatty acids?
How does this affect the cytosolic coenzyme A concentration? (please write the
answer on the back of this page) Answer: The generation of ketone bodies (which
contain no CoA moiety) from acetyl-CoA frees up mitochondrial coenzyme A for
continued fatty acid oxidation. The separation of the coenzyme A pools of the cytosol
and the mitochondrial matrix is maintained by the acyl-carnitine/carnitine transport
system. Ketone body production therefore does not affect the cell’s cytosolic CoA
concentration.