Thread: Q-1) Metabolism N*

Answer E

Originally Posted by Roxanita

In the biosynthesis of glucose from pyruvate by the liver, the first intermediate formed from pyruvate is
A) acetyl CoA
B) alanine
C) lactate
D) methylmalonyl CoA
E) oxaloacetate

My answer is E..

Krebs Cycle1 Krebs CycleOutline - Chapter 11 in Text Reactions of Pyruvate Formation of Oxaloacetate
Formation of Acetyl-CoA
Reactions of Krebs Cycle
Regulation of Krebs Cycle 2 Pyruvate to Oxaloacetate
® Pyruvate ® Oxaloacetate First step in gluconeogenesis
Requires CO2 3 Pyruvate to Acetyl-CoASee text, Figure 11.4, page 295

Reaction occurs inside mitochondria
Partial Net Reaction:
CH3 -C(O)-COO - ® CH3 -C(O)-S-CoA + CO2
Pyruvate oxidized: Oxidative decarboxylation
Lipoic acid undergoes reduction of disulfide group
Dihydrolipoic acid + FAD ® lipoic acid + FADH2 4 Pyruvate Dehydrogenase

Krebs Cycle Pictures and SummaryAs the above diagram illustrates, this is truly a continuous cycle. Acetyl coenzyme A binds to the oxaloacetate in order to convert it to citrate. Water is released from the citrate and then regained in order to form isocitrate. NAD+ binds to isocitrate, leaves as NADH, and carbon dioxide is lost in order to form a-ketoglutarate. NAD+ binds to a-ketoglutarate, leaves as NADH, coenzyme A binds and carbon dioxide is lost in order to form succinyl CoA. Coenzyme A leaves in order to form succinate. FAD binds to succinate and leaves as FADH2 in order to form fumarate. Water binds to fumarate and forms malate. NAD binds to malate and leaves as NADH which creates a new oxaloacetate molecule ready to bind to another acetyl coenzyme A to start the process over again.