Biochemistry Assignment: Multiple Choice Questions and Fill-in-the-Blank

Allosteric enzymes

1.Which of the following describes a characteristic of most allosteric enzymes?

a)They are composed of single subunits.

b)In the absence of effectors, they generally follow Michaelis-Menten kinetics.

c)They show cooperativity in substrate binding.

d)They have allosteric activators that bind in the catalytic site.

e)All of the above

2.The active site of an enzyme

a)is frequently located in a cleft in the enzyme.

b)is the portion of the enzyme to which the substrate binds.

c)contains the reactive groups that catalyze the reaction.

d)All of the above

e)None of the above

3.Which of the following residues cannot be phosphorylated?

a)Alanine

b)Serine

c)Threonine

d)Tyrosine

4.What percentage of Vmax is obtained when the substrate is present at the KM?

a)10%

b)25%

c)50%

d)75%

e)100%

5.The fundamental difference between competitive and noncompetitive inhibition is

a)the degree of cooperativity of the reaction.

b)the size of the active site of the enzyme.

c)the location of binding of substrate on the enzyme.

d)the location of binding of inhibitor on the enzyme.

6.An uncompetitive inhibitor

a)changes the slope of the line formed on a Lineweaver-Burk plot relative to uninhibited enzyme.

b)binds only to the enzyme-substrate complex.

c)does not affect the value of Vmax.

d)increases the value of KM.

7.Enzymatic activity has an optimum temperature because

a)the component amino acids have varying melting points.

b)the rate of reactions is thermodynamically controlled.

c)raising the temperature speeds up the reaction until protein denaturation sets in.

d)the organism dies beyond a certain temperature.

8.In the reaction catalyzed by chymotrypsin, a graph in which the rate is plotted against substrate concentration

a)is sigmoidal, characteristic of an allosteric enzyme.

b)shows that cooperative kinetics are observed.

c)shows that the substrate concentration does not affect the rate.

d)is hyperbolic, characteristic of a non-allosteric enzyme.

9.Which of the following lipid molecules feature carbon rings in their structures?

a)Fatty acids

b)Glycolipids

c)Triglycerides

d)Sphingolipids

e)Steroids

10.Naturally occurring unsaturated fatty acids usually have ____ double bonds.

a)cis

b)trans

c)no

d)five or six

11.How does cholesterol affect membrane fluidity?

a)It tends to increase the fluidity.

b)It tends to decrease the fluidity.

c)It doesn't have any specific effect on fluidity.

d)Membranes don’t have cholesterol.

12.The main difference between active transport and passive transport is that

a)concentration gradients are involved in one and not in the other.

b)glycolipids play a role in one and not in the other.

c)one requires expenditure of energy by the cell and the other does not.

d)ions are transported into and out of the cell by one process and not by the other.

13.Which of the following vitamins is not fat soluble?

a)A

b)C

c)D

d)E

e)K

14.In the _______________________ model of enzyme-substrate binding, an enzyme changes shape upon substrate binding.

15.The sigmoidal behavior of allosteric proteins is a result of _______________________ between the subunits.

16._______________________ are a class of enzymes that move a functional group, such as a phosphate, from one molecule to another.

17.Chymotrypsin is an example of an enzyme that facilitates _______________________, in which water is used to break one molecule into two separate molecules.

18.Enzymes increase the _______________________ of a chemical reaction.

19._______________________ is a measure of the catalytic efficiency of an enzyme under saturating _______________________ conditions, which maximize enzyme activity.

20.Multiple _______________________ of carbonic anhydrase exist throughout our bodies, which means that these enzymes catalyze the same reaction but have different structures.

21.Many digestive enzymes such as chymotrypsin often exist in a precursor state known as the _______________________ form, which is denoted by a pro- prefix or –inogen suffix.

22.Given the structures below, answer the following questions: 

a)Which letter represents a phospholipid?  _____

b)Which letter represents cholesterol?  _____

c)Which letter represents a triacylglyceride?  _____

d)Which letter represents a glycolipid?  _____

e)Which letter represents a saturated fatty acid?  _____

23."Stopate" is an enzyme inhibitor. In the presence of the inhibitor, the enzyme's Vmax is unchanged, but the apparent KM for its preferred substrate is altered.

a) Does this pattern suggest that the inhibitor is competing with the active site?

yes no cannot be determined

b) What kind of inhibition is this most likely to be?

competitive          noncompetitive          uncompetitive

24.The reaction catalyzed by aspartate transcarbamoylase (ATCase) is the first step in a series of reactions leading to the production of CTP. ATP and CTP are effectors of ATCase. 

a)Is ATCase an allosteric enzyme or a non-allosteric enzyme? Circle the correct answer. 

b)Do you expect CTP to be an activator or inhibitor of ATCase? 

25.Explain how the overall shape of fatty acids is affected by cis and trans double bonds.