The Medical College - Page 53
191.
Enzymes function in reactions by:
A.
increasing the net energy yield.
B.
raising the energy level of the
products.
C.
decreasing the energy of
activation.
D.
changing the thermodynamic nature of
a
reaction, thus making a reaction
thermody-
namically favorable when it would not
oth-
erwise be so.
192.
The nature of enzymes requires that the
enzyme
is:
A.
used up in quantities greater than those
of
substrate that is converted to
product.
B.
used up in quantities approximately
equal
to those of substrate that is converted
to
product.
C.
used up in quantities significantly less
than
those of the substrate that is converted
to
product.
D.
essentially not used up and must
be
replaced only in small quantities.
193.
Activity of enzymes is often regulated by
cova-
lent modification. This is most often
accom-
plished by:
A.
phosphorylation/dephosphorylation.
B.
sulfation/desulfation.
C.
substitution of one cation for
another.
D.
substitution of one anion for
another.
194.
The response of most enzymes to being boiled
in
an aqueous solution is:
A.
substantially increased activity.
B.
substantially decreased activity.
C.
an increase of about 1 unit in
isoelectric
point.
D.
no noticeable change is detected.
Passage IX (Questions 195–199)
All of the possible ketopentose sugar isomers
have
been synthesized in a research project. The
ketopentose
isomers have been reduced with sodium
borohydride,
converting the ketone function to an
alcohol.
195.
The total number of 2-ketopentose isomers
is:
A.
two.
C.
six.
B.
four.
D.
eight.
196.
The total number of isomers of the sugar
alco-
hols produced by sodium borohydride
reaction
is:
A.
two.
C.
four.
B.
three.
D.
five.
197.
If all the sugar alcohols in the previous
question
were selectively oxidized so that the number
3
hydroxyl was converted to a ketone, there
would
be __________ chiral center(s) in each
molecule.
A.
one
C.
three
B.
two
D.
four
198.
The pentose(s) found in RNA usually
consists
of:
A.
deoxyribose.
C.
various pentoses.
B.
ribose.
D.
glucose.
199.
If the sugar alcohols in question 196 were
oxi-
dized to convert carbon numbers 1 and 5 to
car-
boxyls, the number of chiral centers would
be:
A.
none.
C.
two.
B.
one.
D.
three.
Passage X (Questions 200–204)
The synthesis of proteins and nucleic acids is
seen as
being directed by a series of coded messages.
The mes-
sages must be sent, received, and
decoded.
200.
The primary source or repository of
information
concerning synthesis of nucleic acids and
pro-
teins is considered to be:
A.
protein.
C.
RNA.
B.
DNA.
D.
peptides.
201.
In the polymer that directs protein
biosynthesis,
there is a requirement of __________ unit(s)
(or
monomers) to code for each amino
acid.
A.
one
C.
three
B.
two
D.
four
202.
In a chromosome of higher animals there is
(are)
__________ strand(s) of DNA.
A.
one
C.
three
B.
two
D.
four
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