Biochemistry Mid-Semester 2 CAT — 2013 (Past Paper)

18 clinical MCQs in Biochemistry. Name the four (4) steps for the successive addition of 2-carbon atoms to a growing chain o. Kenya, Africa and global r...

Questions, Answers & Explanations

1. Q1. Name the four (4) steps for the successive addition of 2-carbon atoms to a growing chain of palmitic acid in the order of occurrence. ( ---

   • ______
   • ______
   • ______
   • ______

   Answer: ______

2. Q2. Glycolysis leads to the production of and two molecules of ATP. In the absence of oxygen, fermentation leads to the production of . Glycolysis plus the TCA cycle can convert the carbons of glucose to , storing the energy as ATP, and . ---

   • Lactate, pyruvate, $\text{CO}_2$, NADH, $\text{FADH}_2$
   • $\text{CO}_2$, NADH, $\text{FADH}_2$, Lactate, pyruvate
   • $\text{O}_2$, Lactate, pyruvate, $\text{FADH}_2$
   • Pyruvate, Lactate, $\text{CO}_2$, NADH, $\text{FADH}_2$
   • Glucose, Lactate, $\text{CO}_2$, NADH, $\text{FADH}_2$

   Answer: Lactate, pyruvate, $\text{CO}_2$, NADH, $\text{FADH}_2$

3. Q3. At the end of glycolysis, each molecule of glucose has yielded two molecules of , two molecules of and a net of two molecules of . ---

   • $\text{H}_2\text{O}$, $\text{CO}_2$, ATP
   • Pyruvate, NADH, ATP
   • Lactate, Ethanol, $\text{CO}_2$
   • $\text{CO}_2$, $\text{NAD}^+$, ADP
   • FAD, $\text{NAD}^+$, ADP

   Answer: $\text{H}_2\text{O}$, $\text{CO}_2$, ATP

4. Q4. The enzyme hexokinase uses ATP to phosphorylate glucose to G6P. The product continues to be oxidized forming pyruvate and eventually acetylCoA. Suppose that a cell has only glucose available for hexokinase is suddenly stopped in this cell. Which of the following conditions will occur? ---

   • The cell will continue to produce energy from mitochondrial electron transport.
   • The cell will continue to produce ATP using the TCA cycle.
   • The cell will ultimately be unable to produce ATP.
   • The cell will be forced to switch to fermentation to produce ATP.
   • The use of oxygen by the cell will increase.

   Answer: The cell will continue to produce energy from mitochondrial electron transport.

5. Q5. As a result of glycolysis, pyruvate oxidation and the TCA cycle, only a small portion of the energy of glucose has been converted to ATP. At this point, majority of the usable energy is contained in ---

   • $\text{NAD}^+$, FAD
   • $\text{CO}_2$
   • Pyruvate
   • AcetylCoA
   • $\text{NADH}$, $\text{FADH}_2$

   Answer: $\text{NAD}^+$, FAD

6. Q6. During a heart attack, blood flowing to the heart muscle is interrupted by blockage of a coronary artery. How would you expect the metabolism in the heart to change? ---

   • Oxidative phosphorylation in the mitochondria would slow down.
   • The rate of production of lactate would be stimulated.
   • The use of glucose by the muscle tissue would increase.
   • The production of water by mitochondria would be inhibited.
   • All above are expected metabolic changes.

   Answer: Oxidative phosphorylation in the mitochondria would slow down.

7. Q7. The standard reduction potential of a relox reaction is a measure of the tendency of the to electrons. ---

   • Reductant, gain
   • Reductant, lose
   • Oxidant, gain
   • Oxidant, lose
   • None of the above

   Answer: Reductant, gain

8. Q8. The oxidation of 3 mol of glucose by the pentose phosphate pathway may result in the production of ---

   • 2 mol of pentose, 4 mol of NADPH and 8 mol of $\text{CO}_2$
   • 3 mol of pentose, 4 mol of NADPH and 3 mol of $\text{CO}_2$
   • 3 mol of pentose, 6 mol of NADPH and 3 mol of $\text{CO}_2$
   • 4 mol of pentose, 3 mol of NADPH and 3 mol of $\text{CO}_2$
   • 4 mol of pentose, 6 mol of NADPH and 3 mol of $\text{CO}_2$

   Answer: 2 mol of pentose, 4 mol of NADPH and 8 mol of $\text{CO}_2$

9. Q9. Which of the following substrates derived from adipose tissues contribute to net gluconeogenesis in human liver? ---

   • Fatty acid
   • Glycerol
   • Pyruvate
   • AcetylCoA
   • propionylCoA

   Answer: Fatty acid

10. Q10. Which statement best describes the oxidation of odd chain fatty acids? ---

    • One carbon is removed
    • Additional enzymes are not required
    • End product is propionylCoA
    • AcetylCoA is also produced
    • The process requires some vitamins

    Answer: One carbon is removed

11. Q11. One and the only energy requiring step in fatty acid oxidation is catalyzed by ---

    • Thiokinase
    • Thiolase
    • AcylCoA dehydrogenase
    • Enoyl dehydratase
    • CAT I

    Answer: Thiokinase

12. Q12. Which of the following is not used for fatty acid synthesis? ---

    • Cobalamine
    • NADPH
    • Biotin
    • Bicarbonate
    • AcetylCoA carboxylase

    Answer: Cobalamine

13. Q13. MalonylCoA is a direct inhibitor of which enzyme of fatty acid oxidation? ---

    • CAT I
    • CAT II
    • AcylCoA synthetase
    • Thiolase
    • None of the above

    Answer: CAT I

14. Q14. The following are conditions of ketosis except ---

    • Starvation
    • Uncontrolled diabetes mellitus
    • Low CHO diet
    • Von Gierke's (Type I GSD) disease
    • All the above

    Answer: Starvation

15. Q15. When the liver converts excess glucose into fatty acids, all of the following are true except ---

    • Glucose is converted by glycolysis into pyruvate in the cytosol.
    • Pyruvate is converted to acetylCoA by the PDH complex in the cytosol.
    • acetylCoA and oxaloacetate form citrate that leaves the mitochondria.
    • Citrate lyase converts citrate, CoA-SH and ATP into oxaloacetate, acetylCoA, ADP and Pi.
    • The acetylCoA is converted to palmitate and the oxaloacetate is converted to pyruvate.

    Answer: Glucose is converted by glycolysis into pyruvate in the cytosol.

16. Q16. The acyl carrier protein (ACP) and CoA have all of the following in common except ---

    • Both incorporate ADP into their structure
    • Both incorporate pantothenate into their structure
    • Both have a functional – SH group
    • Both form thioester bonds with fatty acids
    • Both form high energy bonds with fatty acids

    Answer: Both incorporate ADP into their structure

17. Q17. Starting with an intermediate in glycolysis and acylCoA, all of the following are intermediates in the synthesis of triacylglycerols except ---

    • Monoacylglycerol
    • Glycerol 3-phosphate
    • Monoacylglycerol phosphate
    • Diacylglycerol phosphate
    • Diacylglycerol

    Answer: Monoacylglycerol

18. Q18. Oxidation of fatty acids with an odd number of carbon atoms does not require

    • A decarboxylase
    • Biotin
    • An isomerase
    • A mutase
    • Cyanocobalamine

    Answer: A decarboxylase