Krebs cycle — practice questions

Question 1 · difficulty L1 · recall

Where does the Krebs cycle occur in eukaryotic cells?

• A. Outer mitochondrial membrane
• B. Cytoplasm
• C. Mitochondrial matrix
• D. Golgi apparatus

Question 2 · difficulty L2 · understanding

Before entering the Krebs cycle, pyruvate is converted into which two-carbon compound?

• A. Succinate
• B. Oxaloacetate
• C. Citrate
• D. Acetyl-CoA

Question 3 · difficulty L3 · understanding

Identify the step in tricarboxylic acid cycle, which does not involve oxidation of substrate.

• A. Malic acid $$\rightarrow$$ Oxaloacetic acid
• B. Succinic acid $$\rightarrow$$ Malic acid
• C. Succinyl-CoA $$\rightarrow$$ Succinic acid
• D. Isocitrate $$\rightarrow \alpha$$-ketoglutaric acid

Question 4 · difficulty L3 · understanding

How many times decarboxylation occurs during each TCA cycle?

• A. Thrice
• B. Many
• C. Once
• D. Twice

Question 5 · difficulty L3 · understanding

Match List I with List II: List I List II (A) Oxidative decarboxylation (I) Citrate synthase (B) Glycolysis (II) Pyruvate dehydrogenase (C) Oxidative phosphorylation (III) Electron transport system (D) Tricarboxylic acid cycle (IV) EMP pathway Choose the correct answer from the options given below :

• A. A – II, B – IV, C – I, D – III
• B. A – III, B – I, C – II, D – IV
• C. A – II, B – IV, C – III, D – I
• D. A – III, B – IV, C – II, D – I

Question 6 · difficulty L3 · understanding

Melonate inhibits the growth of pathogenic bacteria by inhibiting the activity of

• A. Amylase
• B. Lipase
• C. Dinitrogenase
• D. Succinic dehydrogenase

Question 7 · difficulty L3 · understanding

The 5-C compound formed during TCA cycle is

• A. Fumaric acid
• B. $$\alpha$$-ketoglutaric acid
• C. Oxalo succinic acid
• D. Succinic acid

Question 8 · difficulty L3 · understanding

The number of time(s) decarboxylation of isocitrate occurs during single TCA cycle is

• A. Four
• B. One
• C. Two
• D. Three

Question 9 · difficulty L3 · understanding

The number of substrate level phosphorylations in one turn of citric acid cycle is

• A. Zero
• B. One
• C. Three
• D. Two

Question 10 · difficulty L3 · application

If oxaloacetate is not regenerated in the Krebs cycle, which immediate consequence follows?

• A. Acetyl-CoA cannot continue entering the cycle efficiently
• B. Glycolysis cannot form pyruvate
• C. Oxygen cannot diffuse into mitochondria
• D. ATP cannot be formed by substrate-level phosphorylation anywhere