Question

1.
Mr A. likes to eat a lot of high energy food and hates to do exercise. Theoretically speaking, will the rate of the citric acid cycle in his body be faster or slower than average? Please explain.

2.
Which of the following modification is normally NOT present in proteins? (please explain)
A. polysaccharide conjugation
B. lipid conjugation
C. polyadenylation
D. phosphorylation

3.
Why is the TCA cycle is the central pathway of metabolism of the cell? (please explain)
A. it occurs in the center of the cell
B. its intermediates are commonly used by other metabolic reaction
C. all other metanolic pathways depend upon it
D. none of the above

4.
In the reaction of converting fructose 6-phosphate to fructose 1,6-biphosphate, which of the following is NOT true? (please explain)
A. the free energy change is highly negative
B. the concentration of ADP af the equilibrium of the reaction is very low
C. the extra phosphate group on fructose 1,6-biphosphate comes from ATP
D. the entropy does not increase after the reaction

5.
After hydrolysis of sucrose into individual monosaccharides, what is the chage in sweetness? please explain
A. remain the same
B. sweeter
C. less sweet
D. as sweet as lactose

Answer 1

1) TCA rate would be slower than average. If energy is obtained from the food eaten and one doesn’t do exercise to use it, then body doesn’t need to create more energy. Thus TCA rate would be lower.

2) Polyadenylation is done for mRNA and not for proteins.

3) TCA intermediates are fed into many other cycles of the cell, thus it is centrally important to metabolism. Its intermediates ensure cross-talk between various cycles, thus allowing for regulation as per metabolic status of cell. Eg, if energy is not needed, TCA won’t be active and thus the intermediates won’t be readily available, thus other pathways dependent on TCA, would also slow down, so that energy is not wasted.

4) ADP concentration at equilibrium sate of reaction can’t be low. The substrates and products are at a steady-state concentration at equilibrium.

5) It becomes sweeter. Glucose and fructose are individually less sweet than sucrose, but if considered together, they add up to more sweetness than their disaccharide sucrose.