LSM1101 Sem1 Enzyme Tutorial

1. The equilibrium constant for the conversion of the disaccharide sucrose to the simple sugars glucose and

fructose is 140,000. What can you conclude about the reaction?

Sucrose + H2O ↔ Glucose + Fructose

A. It never reaches equilibrium.

B. It is a spontaneous reaction, starting with sucrose.

C. The equilibrium constant increases when the starting concentration of sucrose is increased.

D. At equilibrium, the concentration of sucrose is much higher than the concentrations of glucose and fructose.

E. Glucose and fructose exhibit a higher free energy level than sucrose and water.

2. The following set of data was obtained by LSM1101 students.

(a) Draw a plot of Vo against [S]

(b) Explain why the turnover (or the rate of marble transfer from one plastic container to the other) is not

depended on the number of marbles present in the substrate container

(c) Plot a graph of the time it took the student to find and transfer a marble from the substrate to the product

container against # marbles in the substrate container.

3. Enzyme A follows simple Michaelis-Menten kinetics. Its Km and kcat for substrate S are 30 M and 5,000

sec-1, respectively. Does this enzyme approach catalytic perfection?

4. Km and Vmax for two substrates A and B are 4.0 M, 25 mol/sec and 0.5 M, 15 mol/sec, respectively. At low

concentration (<1mM), which substrate will react more rapidly?

5. Liver alcohol dehydrogenase (ADH) can oxidize ethanol or other alcohols, including methanol. Methanol

oxidation generates formaldehyde, which is very toxic, causing blindness. My dog Clancy mistakenly ingested

50 mL of washer fluid (a solution 50% w/w in methanol). Knowing that methanol would be discharged

eventually by Clancy’s kidneys if its oxidation could be blocked, and realizing that, in terms of methanol

oxidation by ADH, ethanol would act as a competitive inhibitor, I decided to offer Clancy some wine.

How much of wine (12% w/w ethanol) must Clancy consume in order to lower the activity of his ADH on

methanol to 5% of its current value?

Assume:

(a) Density of the washer fluid and wine: 0.9 g/ml. (b) Km of ADH for methanol is 10 mM (c) Clancy’s body fluid

volume: 15 L. (d) Dissociation constant Ki of ethanol for ADH is 1 mM.