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Carbohydrate Chemistry and Metabolism Flashcards

6 cards from real Biochemistry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. The Cori cycle involves the transfer of metabolites between muscle and liver. Muscle exports lactate; the liver converts it back to:

    Answer: Glucose via gluconeogenesis, which is returned to muscle

    In the Cori cycle, lactate from anaerobic muscle glycolysis travels to the liver, where gluconeogenesis converts it back to glucose, which is released into the blood for muscle use.

  2. Insulin stimulates glucose uptake in muscle and adipose tissue primarily by:

    Answer: Promoting translocation of GLUT4 transporters to the plasma membrane

    Insulin signaling via PI3K/Akt promotes the translocation of GLUT4-containing vesicles from intracellular stores to the plasma membrane, rapidly increasing glucose uptake.

  3. Glycogen synthase is activated when it is in which phosphorylation state?

    Answer: Dephosphorylated (active)

    Glycogen synthase is active in its dephosphorylated form; phosphorylation by kinases such as GSK-3 inhibits the enzyme, reducing glycogen synthesis.

  4. Galactosemia results from accumulation of galactose-1-phosphate due to deficiency of which enzyme?

    Answer: Galactose-1-phosphate uridylyltransferase (GALT)

    Classic galactosemia is caused by GALT deficiency, which prevents conversion of galactose-1-phosphate to UDP-galactose, leading to toxic accumulation of galactose-1-phosphate in the liver, brain, and kidneys.

  5. Which sugar transporter (GLUT) is expressed in pancreatic beta-cells and serves as a glucose sensor?

    Answer: GLUT2

    GLUT2 in pancreatic beta-cells has a high Km for glucose, allowing glucose uptake proportional to blood glucose concentration, enabling beta-cells to sense and respond to glucose levels.

  6. The net ATP yield from complete oxidation of one molecule of glucose through glycolysis and oxidative phosphorylation is approximately:

    Answer: 30-32 ATP

    Using current estimates of the P/O ratio, complete oxidation of glucose yields approximately 30–32 ATP: 2 from glycolysis, 2 from the TCA cycle substrate-level phosphorylation, and ~26–28 from oxidative phosphorylation.

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