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ENZYMES
1
...
Michaelis constant of enzyme (Km) is:
a) The substrate concentration which gives
maximal velocity
b) The substrate concentration which gives 1/2
the maximal velocity
c) 1/2 the substrate concentration which gives
maximal velocity
d) The enzyme concentration which gives
maximal velocity
e) The enzyme concentration which gives 1/2 the
maximal velocity
3
...
The non-protein part of an enzyme is called:
a) Apoenzyme
b) Holoenzyme
c) Allosteric Enzyme
d) Isoenzyme
e) Coenzyme

5
...
Enzymes:
a) Increase the energy barrier for a reaction
b) Are recovered chemically altered after a
complete reaction
c) Increase the equilibrium constant of the
reaction
d) Activity is subject to regulation
e) Are exclusively proteins
7
...
At Vmax of an enzyme catalyzed reaction:
a) Further increase in substrate concentration
increases the rate of the reaction
b) All the enzyme molecules are combined with
substrate
c) The substrate concentration that produces
maximal velocity is termed Km
d) Half the enzymes are combined with substrate
e) Km is maximum

9
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Isoenzymes:
a) Are factors required for enzyme activity
b) Are functional plasma enzymes
c) Show similar responses to inhibitor molecules
d) Are important tools in the diagnosis &
prognosis of disease
e) Catalyze oxidation-reduction reactions
11
...
Which of the following statements is true of
enzyme catalysts?
a) To be effective they must be present at the
same concentration as their substrate
b) They can increase the equilibrium
constant for a given reaction by a
thousand -fold or more

c) They lower the activation energy for
conversion of substrate to product
d) Their catalytic activity is independent of pH
e) They are generally equally active on D and L
isomers of a given substrate
13
...
The following enzyme complex requires both
thiamine and lipoic acid:
a) Malate dehydrogenase
b) Alpha-ketoglutarate dehydrogenase
c) Fumarase
d) Isocitrate dehydrogenase
e) Succinate dehydrogenase
15
...
In an enzyme catalyzed reaction:

a) Enzymes increase the energy barrier for the
reaction
b) Enzymes form a perminant complex with the
substrate
c) After the reaction, enzymes are recovered
unchanged
d) V-max is reached in the presence of a noncompetitive inhibitor
e) The equilibrium constant is decreased
17
...
Subclasses of oxidoreductases include:
a) Kinases and oxygenases
b) Reductases and dehydrogenases
c) Racemases and oxidases
d) Catalases and aminotransferases
e) Peroxidases and anomerase
19
...
Coenzymes:

a) Are small organic molecules needed for
enzyme activity
b) Are associated with apoproteins
c) Are vitamin derivatives
d) Are called prosthetic groups if they are tightly
bound to the enzyme
e) All of the above is correct
21
...
In non-competitive inhibition of enzyme activity:
a) Both Vmax and Km are increased
b) Inhibitor has no structural resemblance to the
substrate
c) There is a significant alteration of the active
site
d) Vmax is decreased
e) A is the only wrong answer
23
...
The following statements about regulation of
enzyme activity are correct:
a) Phosphorylation/ dephosphorylation is the
common covalent modification
b) Regulatory enzymes usually catalyze
reversible reactions
c) Allosteric inhibitors are usually the end
products
d) Increase in the enzyme level has no effect
e) Irreversible inhibition is physiological type of
regulation
25
...
The enzyme for starch digestion is:
a) Salivary amylase
b) Pancreatic amylase
c) Lysosomal glucosidase
d) Both A and B
e) All of the above is correct

27
...
The following enzymes are absent in muscles but
are present in the liver:
a) Pyruvate carboxylase and citrate synthase
b) Glucose-6-phosphatase and glycerol kinase
c) Lactate dehydrogenase and isocitrate
dehydrogenase
d) Pyruvate dehydrogenase and beta-ketothiolase
e) Glycogen synthase and 3-HMG CoA synthase

29
...
Isoenzymes:
a) Are differentiated by dialysis

b) Show the same electrophoretic mobility
c) Include lactate dehydrogenase
d) Are used as diagnostic tools
e) Both C and D are correct
31
...
Restriction enzymes:
a) Recognize specific nucleotide sequences in
DNA
b) Cut both strands of DNA
c) Often produce single stranded tails
d) Do all of the above
e) Do none of the above
33
...
Enzymes and pH:
a) All enzymes have one optimum pH
b) Enzymes in the stomach require alkaline pH
c) All enzymes in eukaryotic cells require the
same pH

d) The optimum pH is the one at which the
enzyme has maximum activity
e) The pH is the same in the lysosome and plasma
35
...
The following vitamin work as coenzymes with the
corresponding enzyme:
a) Biotin and carboxylases
b) Cobalamin with isomerases
c) Retinol with lyases
d) Riboflavin with hydrolases
e) Thiamin and isomerases



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