Carbohydrate Chemistry and Metabolism Flashcards

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

Answer: AMP

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

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

Answer: CO₂ and NADH

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

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

Answer: NAD⁺

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.

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

Answer: NADPH and ribose-5-phosphate

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

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

Answer: Acetyl-CoA

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.

Von Gierke disease (Type I glycogen storage disease) is caused by deficiency of:

Answer: Glucose-6-phosphatase

Glucose-6-phosphatase deficiency in Von Gierke disease prevents the liver from releasing free glucose from glycogen (or gluconeogenesis), causing severe fasting hypoglycemia.