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Biochemistry

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Glyoxylate Cycle: Reactions and Function

BIOCHM-NEGETB

Plants, but not animals, can carry out reactions of the glyoxylate cycle which, when coupled with some of the reactions of the citric acid cycle, can feed into gluconeogenesis. The overall equation for glycolysis is given below.

${ 2\, \text{Acetyl CoA} \, +\, 2 }{ NAD }^{ + }{ +\, FAD\longrightarrow \text{Oxaloacetate} \,+\,2\,CoA\,+\,2\,NADH\,+\, }{ FADH }_{ 2\, }{ +\, 2\, { H }^{ + } }$

Considering how these 3 pathways (glyoxylate cycle, citric acid cycle, and gluconeogenesis) interconnect, identify which of the following statements is NOT true considering the glyoxylate cycle in plants?

A

The glyoxylate cycle takes place in glyoxysomes.

B

The two enzymes unique to the glyoxylate cycle are isocitrate lyase and malate synthase.

C

In the glyoxylate cycle, 2 acetyl-CoA are converted to succinate in the glyoxysome, and succinate is then transported to the mitochondrion and converted to malate.

D

The glyoxylate cycle is important in seed germination in part for the conversion of stored lipids, through acetyl-CoA, to glucose via gluconeogenesis.

E

Animals do not have glyoxysomes or a glyoxylate cycle and thus, cannot carry out gluconeogenesis.

F

The glyoxylate cycle is able to feed the carbons of acetyl-CoA (from the beta-oxidation of fatty acids) into gluconeogenesis by bypassing the decarboxylation steps in the citric acid cycle where the carbons would normally be lost as ${ CO }_{ 2 }$.