Biochemistry: Enzymes, Metabolism, and ATP Quiz

Grade 12 · Science · Quiz

Test your knowledge of enzyme function, metabolic pathways, and cellular energy production.

Questions

1. Which molecule is the direct product of glycolysis that enters the Krebs cycle (after conversion)?

   1. Glucose
   2. Acetyl-CoA
   3. NADH
   4. ATP
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   Answer: Acetyl-CoA

   Pyruvate (from glycolysis) is converted to Acetyl-CoA in the mitochondrial matrix by pyruvate dehydrogenase complex before entering the Krebs cycle.

2. Increasing temperature always increases enzyme activity.

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   Answer: False

   Enzyme activity increases with temperature up to the optimum (~37°C for human enzymes), then drops sharply as heat denatures (unfolds) the active site, permanently inactivating the enzyme.

3. In aerobic respiration, oxygen is the final electron ___ in the electron transport chain.

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   Answer: acceptor

   Oxygen is the final electron acceptor in the ETC. It accepts electrons and protons to form water (H₂O). Without oxygen, the chain stops and ATP production halts.

4. What is the net ATP yield from glycolysis alone?

   1. 0 ATP
   2. 2 ATP
   3. 4 ATP
   4. 36 ATP
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   Answer: 2 ATP

   Glycolysis uses 2 ATP and produces 4 ATP for a net gain of 2 ATP per glucose. It also produces 2 NADH and 2 pyruvate.

5. Lactic acid fermentation regenerates NAD⁺ to allow glycolysis to continue.

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   Answer: True

   During intense exercise, when oxygen runs out, lactic acid fermentation converts pyruvate to lactate while regenerating NAD⁺, allowing glycolysis to keep producing 2 ATP per glucose.

6. An allosteric inhibitor reduces enzyme activity by:

   1. Binding to the active site
   2. Competing with the substrate
   3. Binding to a site other than the active site, changing its shape
   4. Increasing the activation energy directly
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   Answer: Binding to a site other than the active site, changing its shape

   Allosteric inhibitors bind to a regulatory site distinct from the active site, inducing a conformational change that reduces or eliminates enzyme activity.

7. The Krebs cycle takes place in the mitochondrial ___.

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   Answer: matrix

   The Krebs (citric acid) cycle enzymes are located in the mitochondrial matrix, the innermost compartment of the mitochondrion.

8. NADH carries high-energy electrons to the electron transport chain.

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   Answer: True

   NADH is a high-energy electron carrier. It donates electrons to Complex I of the ETC, and the energy released drives proton pumping and ultimately ATP synthesis.

9. Which coenzyme is reduced during the Krebs cycle and carries electrons to the ETC?

   1. ATP
   2. ADP
   3. NADH
   4. CO₂
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   Answer: NADH

   NADH (and FADH₂) are produced in the Krebs cycle as high-energy electron carriers. They deliver electrons to the ETC, where their energy drives ATP synthesis via oxidative phosphorylation.

10. The overall equation for cellular respiration shows that glucose is broken down into:

    1. CO₂ and H₂O
    2. Lactic acid and CO₂
    3. Ethanol and oxygen
    4. Glucose and water
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    Answer: CO₂ and H₂O

    The overall equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ~36-38 ATP. The carbon skeleton of glucose is completely oxidized to CO₂, while water is formed at the end of the ETC.

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