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King Saud University
College of Science
Department of Biochemistry
BCH 221 – Enzymology
Final Examination
2nd Semester 1419-1420
Name:_____________________________________
No.__________________
Time: 3 hours.
Final Marks
Section 1 ………… /10
Section 2 ………… /40
Section 3 ………… /10
Section 4 ………… /5
Section 5 ………… /25
Section 6 ………… /10
Total: …. /100
Total: …… /60
Final Marks
CAT: _________ /40
Final: _________ /60
Total: _________ /100
Grade: _______
BCH 221 Final
Section 1
Answer the following questions as True [T] or False [F]:
1.
An enzyme can have different Km for the same substrate.
[
]
2.
Eadee-Hofstee plot is obtained when [S]/v is plotted against [S]
[
]
3.
Any substance that binds the active site of an enzyme is known as a substrate. [
]
4.
All enzymes have a quarternary structure.
[
]
5.
Haloenzymes are conjugated proteins.
[
]
6.
Coenzymes are derived from fat soluble vitamins.
[
]
7.
Absence or deficiency of melanin due to deficiency of enzyme tyrosinase
produces albinism.
[
]
8.
pH changes have no effect on the charge on the enzyme.
[
]
9.
Enzymes have an ability to take-in or give-out H+ (protons).
[
]
10.
The maximum absorption at 280 nm given by enzymes is due to the
presence of aromatic amino acids.
[
]
11.
At the isoelectric pH the enzyme has no negative or positive charge.
[
]
12.
Standard free energy (G°) is the difference in the energy level of
transition state and reactants.
[
]
According to the international classification of enzymes, enzymes are placed
in 6 classes depending on the substrate on which they act.
[
]
The following reaction will be catalysed by an enzyme belonging to class 6
of enzyme classification: A - B + C  A-C + B
[
]
15.
Glucokinase is an enzyme with absolute specificity.
[
]
16.
Velocity (v) of the following reaction S  P is equal to –d[p]
dt
t½ is the time in which the concentration of substrate is reduced to half
its original concentration.
[
]
[
]
13..
14.
17.
Page 2 of 11
18.
BCH 221 Final
In the Lineweaver-Burk plot the intercept on the axis on which 1/[S] is
plotted is equal to 1/Km.
[
]
19.
When v is plotted against v/[S] the slope of the line gives-Km.
[
]
20.
If a non-competitive inhibitor is added to reaction E + S
P + E, the
concentration of free enzyme [EF] is equal to: [ET]-ES]-[EI)
[
]
Section 2
In this Section each statement is followed by FOUR related statements which may be all
true, all false or a mixture of true and false. Put [T] in front of the true statement and [F]
in front of the false one:
1.
Different coenzymes are involved in different reactions:
(a)
(b)
(c)
(d)
2.
Coenzyme A transports acyl groups.
FAD transports CO2.
All carboxylases used biotin.
NAD+ is involved in H+ transport.
[
[
[
[
]
]
]
]
[
[
[
[
]
]
]
]
In the following curve:
(a)
(b)
(c)
(d)
[S] represents molar concentration of substrate.
Point (b) is called the initial velocity.
Point (c) is due to mixed order reaction.
Point (a) occurs as the rate is independent of substrate concentration.
Page 3 of 11
BCH 221 Final
3.
Cofactors:
(a)
(b)
(c)
(d)
4.
]
]
]
[
]
Tyrosine.
Histidine.
Phenylalanine.
Threonine.
[
[
[
[
]
]
]
]
[
[
[
[
]
]
]
]
[
[
[
[
]
]
]
]
[
[
]
]
[
]
[
]
The following enzymes belong to class I of enzyme classification:
(a)
(b)
(c)
(d)
6.
[
[
[
Enzymes give a maximum absorption at 280nm. This is due to the presence of:
(a)
(b)
(c)
(d)
5.
are always organic molecules.
combine with haloenzyme to form apoenzyme.
are generally stable to heat.
are essential for the activity of the enzyme which requires the
specific cofactor.
Oxygenases.
Aldolases.
Carboxylases.
Reductases.
The following reaction:
Glucose + ATP
Glucose-6-phosphate + ADP
is brought about by enzymes
(a)
(b)
(c)
(d)
7
belonging to class 2 of enzyme classification.
generally known as kinases.
lyases.
synthetases.
The specific activity of an enzyme was 240 and you had 2 mg of this enzyme:
(a)
(b)
(c)
(d)
Each mg has 240 units of enzyme activity.
Each mg has 120 units of enzyme activity.
You purified this enzyme more and the specific activity become
360. This means that the amount of protein decreased.
During heating the specific activity decreased as protein
concentration increased.
Page 4 of 11
BCH 221 Final
8.
Spectrophotometer can be used to study the following enzymic reactions:
(a)
(b)
(c)
(d)
9.
[
[
[
[
]
]
]
]
is a constant.
Shows the affinity between enzyme and substrate.
is decreased by presence of competitive inhibitors.
= k-1+k+2.
k+1
[
[
[
[
]
]
]
]
[
[
[
[
]
]
]
]
Km:
(a)
(b)
(c)
(d)
10.
Fumerate
malate.
G-6-P+NADP
6-phospho-gluconolactone + NADPH
Phosphoenol pyruvate + ADP
Pyruvate + ATP.
+
+
Dehydrogenases using NAD or FAD as H -ion acceptor.
If we plot 1/v vs [I] at two different substrates concentration, we obtained the
following graph:
(a)
(b)
(c)
(d)
This indicates competitive inhibition.
This is the Lineweaver and Burk plot.
Point (c) on the graph gives -Ki.
Point (b) gives - 1/km.
Page 5 of 11
BCH 221 Final
Section 3
In this Section each statement is followed by four related statements, only ONE of which is
correct, put [T] in front of the correct answer.:
1.
Enzymes:
(a)
(b)
(c)
(d)
2.
are only coenzymes.
are strongly linked to the enzyme protein.
may be removed from an enzyme molecule without loss of activity .
are only metal ions.
[
[
[
[
]
]
]
]
can bind a competitive inhibitor.
can be altered without loss of enzyme activity.
binds noncompetitive inhibitors.
is always hydrophobic.
[
[
[
[
]
]
]
]
[
[
[
[
]
]
]
]
When pH of an enzyme catalysed reaction is changed from pH 8.6 to 12.5:
(a)
(b)
(c)
(d)
5.
]
]
]
]
Active site of an enzyme:
(a)
(b)
(c)
(d)
4.
[
[
[
[
Prosthetic groups:
(a)
(b)
(c)
(d)
3.
increase rate of reaction by decreasing Gibbs Free Energy G°.
are changed during catalytic reactions.
are all simple proteins.
do not change K equilibrium of a reaction.
the enzyme becomes positively charged.
the enzyme precipitates.
the rate of reaction increases.
the enzyme becomes negatively charged.
The following substrate:
Page 6 of 11
BCH 221 Final
R
H2N – C – COOH
H
is optically active as:
(a)
(b)
(c)
(d)
6.
it has one –NH2 group.
it has one COOH group.
it has one R group.
it has assymetric C atom.
(a)
(b)
(c)
(b)
is endothermic.
must get energy from another source to proceed.
has negative (-) value for G°.
has positive (+) value for G°.
]
]
]
]
a ligase.
a lyase.
an isomerase.
a transferase.
[
[
[
[
]
]
]
]
[
[
[
[
]
]
]
]
[
[
[
[
]
]
]
]
The following coenzymes are not involved in H+ transfer:
(a)
(b)
(c)
(d)
9.
[
[
[
[
P + 5 Kcal (energy)
The number of an enzyme is 5.3.4.7: It is:
(a)
(b)
(c)
(d)
8.
]
]
]
]
A reaction:
A
7
[
[
[
[
FAD+.
NADP+
FMN.
Coenzyme A.
The enzyme protease:
(a)
(b)
(c)
(d)
has absolute specificity.
is a hydrolase.
links amino acids to form proteins.
belongs to class 2 of the enzyme classification.
Page 7 of 11
BCH 221 Final
Which of the following methods is most appropriate to study the following
reaction:
10.
Pyruvate + CO2
Oxaloacetate.
Pyruvate carboxylase
(a)
(b)
(c)
(d)
Electrode method.
Fluorescence method.
Spectrophotometric method..
Manometric method.
[
[
[
[
]
]
]
]
Section 4
Complete the following Table for an enzyme extracted from potatoes:
Step
Total
volume
Total
units
protein/m
l
Specific
activity
purification
Yield
(%)
Extract
4520
20450
30
………
1
100
(NH4)SO4
Precipitation (4045%)
590
18290
……
4.2
………
……..
370
…….
1.4
48.0
……..
……..
100
15400
0.21
……….
……….
………
DEAE
Cellulose (eluate)
Affinity
chromato-graphy
(eluate)
Page 8 of 11
BCH 221 Final
Section 5
Write short notes on the following:
1.
Significance of enzymes in diagnosis.
[5 Marks}
2.
Enzyme specificity.
[5 Marks]
Page 9 of 11
BCH 221 Final
[5 Marks]
3.
What are inhibitors and what are their uses.
4.
Propeties of enzymes.
[5 Marks]
5.
Methods for assaying enzymes.
[5 Marks]
Section 6
Page 10 of 11
BCH 221 Final
Section 6
In an experiment carried out in your BCH 221 laboratory the following initial velocity
was obtained when different amounts of substrate were added to a fixed amount of enzyme.
The experiment was repeated again in presence of 0.00022M inhibitor.
v (µmol/min)
S (mmol/l)
without I
with I
1.0 x 10-1
28
17
1.5 x 10-1
36
23
2.0 x 10-1
43
29
5.0 x 10-1
65
50
7.5 x 10-1
74
61
Using Lineweaver-Burk plot determine Km, Ki and Vmax in presence and absence of
inhibitor. What is the type of this inhibitor.
Page 11 of 11