Exam 6: Enzymes

The enzymatic activity of lysozyme is optimal at pH 5.2 and decreases above and below this pH value.Lysozyme contains two amino acid residues in the active site essential for catalysis: Glu³⁵ and Asp⁵².The pK value for the carboxyl side chains of these two residues are 5.9 and 4.5,respectively.What is the ionization state of each residue at the pH optimum of lysozyme? How can the ionization states of these two amino acid residues explain the pH-activity profile of lysozyme?

Which of the following is true of the binding energy derived from enzyme-substrate interactions?

Why does pH affect the activity of an enzyme?

What is a zymogen (proenzyme)? Explain briefly with an example.

The number of substrate molecules converted to product in a given unit of time by a single enzyme molecule at saturation is referred to as the:

For the reaction E + S $\rightarrow$ ES $\rightarrow$ P the Michaelis-Menten constant,K_m,is actually a summary of three terms.What are they? How is K_m determined graphically?

Which of these statements about enzyme-catalyzed reactions is false?

Which one of the following is not among the six internationally accepted classes of enzymes?

The Lineweaver-Burk plot is used to:

Give the Michaelis-Menten equation and define each term in it.Does this equation apply to all enzymes? If not,to which kind does it not apply?

Write an equilibrium expression for the reaction S $\rightarrow$ P and briefly explain the relationship between the value of the equilibrium constant and free energy.

Which of the following statements is false?

The role of an enzyme in an enzyme-catalyzed reaction is to:

Chymotrypsin belongs to a group of proteolytic enzymes called the "serine proteases," many of which have an Asp,His,and Ser residue that are crucial to the catalytic mechanism.The serine hydroxyl functions as a nucleophile.What do the other two amino acids do to support this nucleophilic reaction?

Both water and glucose share an -OH that can serve as a substrate for a reaction with the terminal phosphate of ATP catalyzed by hexokinase.Glucose,however,is about a million times more reactive as a substrate than water.The best explanation is that:

Which of the following statements about allosteric control of enzymatic activity is false?

Define the terms "cofactor" and "coenzyme."

Michaelis-Menten kinetics is sometimes referred to as "saturation" kinetics.Why?

In a plot of l/V against 1/[S] for an enzyme-catalyzed reaction,the presence of a competitive inhibitor will alter the:

Why is a transition-state analog not necessarily the same as a competitive inhibitor?