Biochemistry Carbohydrate Chemistry and Metabolism 2

Question 1

Phosphofructokinase-1 (PFK-1) is the key regulatory enzyme of glycolysis. Which molecule allosterically activates it?

Accepted Answer

AMP

Answer

AMP (and ADP) allosterically activates PFK-1, signaling low energy status in the cell and stimulating glycolysis to increase ATP production.

Question 2

Pyruvate dehydrogenase complex (PDC) converts pyruvate to acetyl-CoA with release of:

Accepted Answer

CO₂ and NADH

Answer

PDC catalyzes the oxidative decarboxylation of pyruvate: pyruvate + CoA + NAD⁺ → acetyl-CoA + CO₂ + NADH, using five cofactors including thiamine pyrophosphate.

Question 3

Under anaerobic conditions in muscle, pyruvate is converted to lactate to regenerate:

Accepted Answer

NAD⁺

Answer

Lactate dehydrogenase reduces pyruvate to lactate, oxidizing NADH back to NAD⁺, which is required for glycolysis to continue producing ATP in the absence of oxygen.

Question 4

The pentose phosphate pathway (PPP) primarily generates which two products needed for biosynthesis?

Accepted Answer

NADPH and ribose-5-phosphate

Answer

The oxidative PPP produces NADPH for reductive biosynthesis and antioxidant defense, and ribose-5-phosphate for nucleotide synthesis.

Question 5

Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors. Which of the following is NOT a gluconeogenic precursor?

Accepted Answer

Acetyl-CoA

Answer

Acetyl-CoA cannot be converted to net glucose in mammals because the two carbons entering the TCA cycle as acetyl-CoA are lost as CO₂ before the cycle can regenerate oxaloacetate.

Biochemistry Practice Test

Biochemistry Practice Test

Biochemistry Carbohydrate Chemistry and Metabolism 2