Concepts in Biochemistry, Chapter 5

1. Enzymes are catalysts. They increase the rate of chemical reactions by:
A.Raising the activation energy
B.Stabilizing the transition state
C.Temporarily increasing the temperature
D.Covalently binding the substrate


2. Shown below is a graph describing energy versus reaction coordinate for a catalyzed and uncatalyzed reaction. Fill in the blanks with the letter that corresponds to each stage of the graph.

_____ ES
_____ S (substrate)
_____ P (product)
_____ Uncatalyzed reaction

Answer:


3. Some enzymes require another chemical to function. These helper compounds are called __________. If a cofactor is covalently bound to the enzyme, it is called a __________ group. An enzyme with its cofactor attached is called a __________, while an enzyme minus its extra component is called an __________.

Answer:


4. Enzymes are classified by the:
A.Size of the enzyme
B.Size of the substrate
C.Type of reaction they catalyze
D.Rate of reaction


5. The Michaelis-Menten equation is vo=Vmax [S]/(Km+[S]).
Fill in the blanks with the letters shown to correctly label each part of the graph.

_____ Vmax
_____ [S]
_____ vo
_____ Point used to determine the Km

Answer:


6. The turnover number of an enzyme is the rate at which product is formed.
E+S ES - k3 E+P
turnover number=k3=Vmax/[ET]
This is the maximum rate of product formation if all of the enzyme substrate binding sites are filled. What can the turnover number tell us about an enzyme?
A.Number of binding sites
B.Reaction mechanism
C.Substrate concentration
D.Enzyme efficiency


7. Often the kinetic values of an enzyme are plotted using the Lineweaver-Burk equation:
1/vo=Km/Vmax·1/[S] +1/Vmax
Enter "yes" or "no" to indicate if the equation and graphical terms match in each statement.
_____ Y-intercept and -1/Km
_____ X-intercept and 1/Vmax
_____ Slope and Km/Vmax

Answer:


8. Which of the following does not influence enzyme activity?
A.pH
B.Temperature
C.Product degradation
D.Effectors
E.Substrate concentration


9. Enzymes carry out different chemical reactions in catalysis. Fill in the blanks with the name of the mechanism that matches with the example described in each line. Mechanism names to choose from are: covalent catalysis, acid-base catalysis, and metal ion catalysis.
__________ catalysis may involve glu, asp, his, lys, or arg residues.
__________ catalysis may involve Na+, K+ or Mg2+, Ca2+.
__________ catalysis may involve serine proteases.

Answer:


10. Enzyme action can be influenced by the presence of inhibitors. Which of the following statements correctly matches the type of inhibitor with its effect on an enzyme.
A.Irreversible and Renders the enzyme permanently inactive
B.Competitive and Inhibitor binds only to ES complex, only important when [S] high, Vmax lower, Km lower
C.Noncompetitive and Can be overcome with high [S]; Vmax unchanged, Km higher
D.Uncompetitive and Cannot be overcome with high [S]; Vmax lower, but Km unchanged



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