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Bio301 Biochemistry
Final Examination (January 25, 2002)
Choose 6 of the 8 to answer among questions 1 to 8 (each 5 point).
Choose 7 of the 8 to answer among questions 9 to 16 (each 10 point)
Question 1
Which of the following are mechanisms for the regulation of the catalytic
activity of enzymes?
a) the binding of regulatory proteins
b) the covalent modification of tryptophan residues
c) the proteolytic cleavage of an inactive enzyme precursor
d) the binding of regulatory peptides via disulfide bonds
Question 2
Which of the following statements is true? Enzyme catalysis of a chemical
reaction
a) decreases G’ so that the reaction can roceed spontaneously.
b) Increases the energy of the transition state.
c) Does not change Go’,but it changes the ratio of products to reatants.
d) Decreases the entropy of the reaction
e) Increases the forward and reverse reaction rates
Question 3.
State whether the following statements are true or false:
A transition state analog for an enzyme-substrate complex
a) fits better in the active site than the substrate.
b) increases the rate of product formation.
c) is a potent inhibitor of the enzyme.
d) can be used to produce catalytic antibodies.
Question 4.
If the standard free-energy change (Go) for a reaction is zero, which of the
following statements about the reaction are true?
a) The entropy (So) of the reaction is zero.
b) The enthalpy (Ho) of the reaction is zero.
c) The equilibrium constant for the reaction is 1.0.
d) The reaction is at equilibrium.
e) The concentrations of the reactants and products are all 1M at equilibrium.
Question 5.
Which of the folowing statements is correct?
The turnover number for chymotrypsin is 100 s-1, and for DNA polymerase it
is 15 s-1. This means that
a) chymotrypsin binds its substrate with higher affinity than does DNA
polymerase.
b) The velocity of the chymotrypsin reaction is always greater than that of
the DNA polymerase reaction.
c) The velocity of the chymotrypsin reaction at a particular enzyme
concentration and saturating substrate levels is lower than that of the
DNA polymerase reaction under the same conditions.
d) The velocities of the reactions catalyzed by both enzymes at saturating
substrate levels could be made equal if 6.7 times more DNA polymerase
than chymotrypsin were used.
Question 6.
The kinetic data for an enzymatic reaction in the presence and absence of
inhibitors are plotted in the figure below. Identify the curve that corresponds
to each of the following:
a) no inhibitor
b) noncompetitive inhibitor
c) competitive inhibitor
d) mixed inhibitor
Question 7.
In the figure below variation of enzyme activity with pH is shown. Which of
the following pairs of amino acids would be likely candidates as catalytic
groups:
a) glutamic acid and lysine
b) aspartic acid and histidine
c) glutamic acid and aspartic acid
d) histidine and histidine
e) histidine and cysteine
pKa values of the side chains of the
above aminoacids are
Asp 3.9, Glu 4.3, His 6.0, Cys 8.3, Lys 10.8
Question 8.
Which of the following answers complete the sentence correctly?
The three enzymes trypsin, elastase and chymotrypsin
a) evolved from a common ancestor.
b) have major similarities in their amino acid sequences and three
dimensional structures.
c) catalyze the hydrolysis of a peptide bond.
d) catalyze reactions that proceed through a covalent intermediate.
e) have identical structure at their substrate binding sites.
Choose 7 of the 8 questions to answer among questions 9 to 16.
Question 9.
a) Draw a tripeptide (anyone you want). Show the main chain, side
chains, a peptide bond, amino and carboxy terminal of this peptide. (5 points)
b) Name the interactions which stabilize tertiary structure of proteins.
(5 points)
Question 10.
The KM of a Michaelis-Menten enzyme for a substrate is 1.0x10-4M. At a
substrate concentration of 0.2M, vo=43M/min for a certain enzyme
concentration. However, with a substrate concentration of 0.02M, vo has the
same value.
a) Using numerical calculations, show that this observation is accurate.
b) What is the best range of [S] for measuring KM?
Question 11.
Calculate the value for K’eq for a reaction that corresponds to
Go’= 1 kcal/mol at 25oC. Show your calculations.
R=1.987x10-3 kcalmol-1deg-1
Question 12.
An oligonucleotide, pApUpGpUpAp is cleaved with
pancreatic ribonuclease in the presence of H2O labelled
with 18O. Show on the figure where the bonds are broken
and which product contain18O. Explain your answer.
Question 13.
Describe the following: (what they are, their use, function, or definition)
a) SDS:
b) 2-mercaptoethanol:
c) puromycin:
d) okazaki fragments:
e) apoprotein:
Question 14.
Ribosomal RNA actively participate in protein synthesis. Name the evidences
strongly supporting this view.
Question 15.
What is a promoter? Describe or draw a simple picture of an eucaryotic RNApol II promoter. What is the difference between a promoter and an enhancer?
Question 16.
What property of DNA allows the repair of some residues damaged through
the action of mutagens?
Describe the sequence of events and the enzymatic activities involved to
repair i.e. UV damage.