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Biochemistry Flashcards

7 cards from real PCAT 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. Which enzyme catalyzes the committed step of glycolysis?

    Answer: Phosphofructokinase-1

    Phosphofructokinase-1 (PFK-1) catalyzes the phosphorylation of fructose-6-phosphate to fructose-1,6-bisphosphate, which is the committed and rate-limiting step of glycolysis.

  2. What is the primary function of ubiquinone (CoQ) in the electron transport chain?

    Answer: Transfers electrons from complexes I and II to complex III

    Ubiquinone (CoQ) is a mobile electron carrier that collects electrons from NADH (via Complex I) and FADH2 (via Complex II) and transfers them to Complex III.

  3. Which amino acid serves as the direct precursor for dopamine biosynthesis?

    Answer: Tyrosine

    Tyrosine is hydroxylated to L-DOPA by tyrosine hydroxylase, then decarboxylated to dopamine by DOPA decarboxylase.

  4. A patient with a deficiency in glucose-6-phosphatase would be unable to perform which process?

    Answer: Glycogenolysis releasing free glucose to blood

    Glucose-6-phosphatase, found mainly in the liver, removes the phosphate from glucose-6-phosphate so free glucose can be exported into the bloodstream; its deficiency causes Von Gierke disease.

  5. In the urea cycle, which nitrogen-containing compound directly donates one of the two nitrogen atoms incorporated into urea?

    Answer: Aspartate

    Aspartate donates its amino group to argininosuccinate, contributing the second nitrogen atom of urea; ammonia provides the first nitrogen via carbamoyl phosphate.

  6. Which of the following best describes the Km value of an enzyme?

    Answer: The substrate concentration at which velocity is half of Vmax

    Km (Michaelis constant) is the substrate concentration at which the reaction velocity equals half of Vmax, and it reflects the affinity of the enzyme for its substrate.

  7. Which vitamin is required as a cofactor for pyruvate dehydrogenase complex activity?

    Answer: Vitamin B1 (thiamine)

    Thiamine pyrophosphate (TPP), derived from vitamin B1, is an essential cofactor for pyruvate dehydrogenase, enabling oxidative decarboxylation of pyruvate to acetyl-CoA.