TMJC H2 Bio data response questions (Ans)

Tampines Meridian Junior College JC2 H2/9744 Biology Data Response Practice (Ans) PRACTICE 1 Pyruvate dehydrogenase is a tetrameric enzyme found in the mitochondria that catalyses the conversion of pyruvate to acetyl CoA during cellular respiration. The activity of pyruvate dehydrogenase is inhibited by acetyl Co-A. Fig. 1 shows the relationship between the initial rate of reaction of pyruvate dehydrogenase activity and the concentration of pyruvate at the optimal temperature and pH of the enzyme. All other variables are kept constant. Fig 1 OR

(a) Comment on the trend shown on the graph. [HI2] [6] • [Describe] As the concentration of pyruvate increases from 0 to 0.02 moldm-3, the rate of reaction increases gradually from 0 molmin-1 to 0.01 molmin-1. • [Explain] At low pyruvate concentrations, the inactive form of the pyruvate dehydrogenase is favoured. / Only a small number of enzymes are able to form enzyme-substrate complexes per unit time. • [Describe] As the concentration of pyruvate increases from 0.02 moldm-3 to 0.04 moldm- 3, the rate of reaction increases steeply from 0.01 molmin-1 to (0.044 - 0.045) molmin-1 (sigmoidal curve) • [Explain] The substrate binds to one active site in the enzyme and causes a conformational change in the enzyme, hence, stabilising the other subunits in the active form and increases the affinity for binding to its substrate molecules. • [Describe] As the concentration of pyruvate increases from (0.057-0.059) moldm-3 to 0.10 moldm-3, the rate of reaction plateaus/remains constant at 0.05 molmin-1. • [Explain] All active sites of all pyruvate dehydrogenase molecules are saturated with pyruvate molecules. (b) On Fig 1, sketch and label a curve to show the effect of adding acetyl Co-A on the initial rate of reaction of pyruvate dehydrogenase activity. [HI 1][1] • Graph should show a lower initial rate of reaction over the entire range of pyruvate concentrations. Graph may reach the Vmax of the normal graph or not reach it. Describe + Explain

PRACTICE 2 Fig. 2 shows the effect of increasing temperature on the activity of three protein -digesting enzymes: • thermitase from thermophilic Thermoactinomyces vulgaris • subtilisin from Bacillus subtilis • modified subtilisin Fig. 2 (a) Describe, with reference to Fig. 2, the effect of temperature on the rate of protein digestion by thermitase. [HI-1] [3] • As temperature increases from 10C to 40 C, rate of protein digestion increases gradually from 0 a.u. to 120 a.u. • As temperature increases from 40C to 76C, the rate increases steeply from 120 a.u. to 650 a.u. • At optimum temperature of 76C, rate of protein digestion is at its maximum. • As temperature increases from 76C to 90C, the rate decreases steeply from 650 a.u. to 350 a.u. Describe means “describe trend of graph and cite data