Question

Some enzymes have a very flat pH profile m dash that is, they have essentially the same activity over a broad pH range. How might you explain this observation? Michaelis-Menten Kinetics. Figure 6-19 represents a Michaelis-Menten plot for a typical enzyme, with initial reaction velocity plotted as a function of substrate concentration. Three regions of the curve are identified by the letters A, B, and C. For each of the statements that follow, indicate with a single letter which one of the three regions of the curve fits the statement best. A given letter can be used more than once. The active site of an enzyme molecule is occupied by substrate most of the time. The active site of an enzyme molecule is free most of the time. The range of substrate concentration in which most enzymes usually function in normal cells. Includes the point (K_av V_max/2). Reaction velocity is limited mainly by the number of enzyme molecules present. Reaction velocity is limited mainly by the number of substrate molecules present.

Answer 1

a) The active site of the molecule is occupied by substrate most of the time - C , because at C the active sites of the enzymes are saturated with substrate molecules, blocking further action.

b) The active site of the molecule is free most of the time - A. At stage A, the active sites of the enzymes are ready and free to combine with substrate molecules to form enzyme substrate complex.

c) The range of substrate concentration at which most of the enzymes function in normal cells - B and C. These are the states at which all the enzyme molecules combine or have combined with the substrate molecules.

d) Includes Km, Vmax/2 - B. At B, the velocity of the enzyme reaction corresponds to exactly one half of the maximal velocity and enzyme substrate saturation is exactly half (Vmax/2). The substrate concentration whic produces one half of the maximal velocity is the Km value.

e) Relative velocity is limited mainly by the number of enzyme molecules present - C. At this stage, the active sites of enzyme limits the number of substrate molecules to bind and form a complex.

f) Relative velocity is limited mainly by the number of substrate molecules present - A. This stage marks the initial velocity at which the concentration of the substrate is very low.