CHM 365
Exam 2
Oct. 13, 2004
Name:
Do all of the questions.
Part I. All questions are worth 5 points each.
Multiple Choice: Circle the single, best answer
1.
All of the following statements are true about the relationships between [S], Km and Vmax EXCEPT:
a) As the [S] is increased, v approaches the limiting value, Vmax.
b) Km = Vmax /2.
c) The rate of the reaction, v, follows a first order rate equation
v = K'[A] and K' = Vmax/K m.
d) The rate of product formed, v, is at Vmax when [S] is high ([S]>>>Km)
e) Km and Vmax assist in finding the rate of the enzyme catalyzed reaction
2.
The molecule shown to the right is:
a)
b)
c)
d)
e)
3.
NAD+
NADH
FADH2
FAD
ATP
Which separation technique uses an applied electric field to separate peptides and proteins?
a) isoelectric focusing
d) SDS PAGE
4.
c) PAGE
Changes in protein conformation can be detected rapidly by:
a)
b)
c)
d)
e)
5.
b) capillary electrophoresis
e) All of the above
ultraviolet absorbance spectroscopy
Edman Sequencing
X-ray diffraction
Mass spectrometry
Reverse-phase HPLC
Edman degradation will:
a) determine the C-terminal amino acid by using a carboxypeptidase.
b) cleave the protein into a multitude of smaller peptides.
c) compare overlapping sets of peptide fragments.
d) determine the N-terminal amino acid.
e) generate two different, but overlapping sets of peptide fragments.
6.
An enzyme's specificity can be due to:
a) the ratio of catalyzed rate to the uncatalyzed rate of reaction
b) molecular recognition based on structural complementarity
c) amount of enzyme produced by the cell
d) amount of substrate available
e) metabolic activators
7.
All of the following are correct statements about enzyme regulation EXCEPT:
a) Enzymes can be inhibited by the products they produce.
b) Enzymes can be inactivated by the addition of a functional group.
c) Coenzyme and substrate availability can regulate enzyme reaction rate.
d) The reaction rate slows as equilibrium is approached.
e) The activity of an enzyme is covalently affected by allosteric regulators.
Short Answer:
8.
Circle all of the following statements that are true about mixed inhibition:
a) The inhibitor interacts with the enzyme as well as the enzyme-substrate complex.
b) Increasing the concentration of [S] can overcome the inhibition.
c) The Vmax value does not remain the same as for a reaction that is not inhibited.
d) The inhibitor can cause a conformational change in the enzyme.
e) The inhibitor binds to a different site than does the substrate.
9.
Circle all of the following that are true statements about the transition state of a reaction:
a) The transition state concentration is equal to the rate of the reaction.
b) The transition state is located at the height of a free energy diagram.
c) The energy required to raise the average energy of one mole of reactant to the transition state is the
free energy of activation.
d) Reaching the transition state indicates that there is a high probability that the reaction will occur.
e) The transition state describes the energetic relationship between the reactants and products.
10.
Use the Lineweaver-Burke plot shown to the right to answer these questions.
a) What is the Km value for the enzyme?
b) What is the Vmax value for the enzyme?
c) What type of inhibitor is depicted on the plot?
11.
What class of enzymes is invo lved in the following reactions?
a)
b)
12.
For a given enzyme, what fraction of the enzyme molecules would have a bound substrate when
[S]=3Km?
13.
Given the peptide STYKVLRAIHG: Show the amino acid sequence of the resulting peptides when this
peptide is cleaved with trypsin.
Essay:
14.
Explain how isoelectric focussing works.
15.
Design an experiment that could be conducted in the lab to determine whether a bisubstrate enzyme
follows a Ping Pong mechanism or a Sequential mechanism.
16.
The catalytic action of an enzyme occurs with the substrate bound at the active site. How can the
binding of another chemical at a point distant from the active site (allosteric modulator) influence the
catalytic activity of the enzyme?
The following questions are worth 8 pts each:
17.
A hexapeptide contains the following amino acids:
Met Phe Lys Ser Trp Leu
Determine the sequence of the peptide using the following data.
a) One round of Edman degradation yielded the PTH derivative:
b) Treatment of the peptide with trypsin yielded a dipeptide with a +1 charge at physiological pH and a
neutral tetrapeptide.
c) Treatment of the peptide with cyanogen bromide yielded two tripeptides.
d) Treatment of the peptide with chymotrypsin yielded a free F and a pentapeptide.
18.
Given the following information about three peptides:
Sequence
RSTYDHQ
GADTEAV
MQHRFWLY
Molecular Weight
906 amu
662 amu
1180 amu
pI Value
7.3
4.2
8.6
a) What order will the peptides be eluted from a capillary electrophoresis column using a buffer with a
pH of 7.4? (Be sure to tell which is first and last).
b) Show the separation of peptides by polyacrylamide gel electrophoresis with SDS (SDS-PAGE).
19.
Explain the function of each of the amino acids in the active site of a serine protease.
Answers:
6. B
7. E