The Medical College - Page 73
187.
A.
Because GMP-140 coating of dishes
increased neutrophil attachment (Figure 1),
the
neutrophils clearly attach to GMP-140.
Pretreat-
ment of neutrophils with GMP-140 (Figure
3)
decreased attachment of the neutrophils to
cul-
tured endothelial cells, indicating that the
GMP-
140 binding sites on neutrophils are involved
in
endothelial attachment.
188.
D.
Treatment of neutrophils with
antibody
against CD-18 had no effect on attachment
of
neutrophils to GMP-140-coated dishes, so
CD-18
on neutrophils is apparently not
involved.
189.
A.
Neutrophils and macrophages (derived
from
monocytes) are most important in
phagocytosis
and if these cells could not easily leave
vessels in
inflammation sites, phagocytosis of
bacteria
should be impaired. Lymphocytes would not
be
affected because they do not appear to depend
on
GMP-140, so natural killer activity (due to
large
granular lymphocytes), cell-mediated
responses
(using helper T lymphocytes and cytotoxic T
lym-
phocytes), and humoral responses (using helper
T
lymphocytes and B lymphocytes) should not
be
heavily affected. Some reduction in
cell-mediated
and humoral responses could occur due to
reduc-
tion in macrophages available to serve as
antigen-
presenting cells and/or cytokine
sources.
190.
B.
Enzymes are generally proteins in
nature,
thus largely polymers of amino acids. Some
other
material may be present as well. The
recent
recognition of a small number of nucleic
acids
(ribozymes) that act as enzymes does not
invali-
date the question.
191.
C.
Enzymes function in reactions by
decreasing
the energy of activation. The net energy
yield
(positive or negative) is not affected, and a
ther-
modynamically unfavorable reaction will not
pro-
ceed simply by addition of an
enzyme.
192.
D.
Enzymes are considered not to be used up
in
reaction. Incidental loss or destruction of
enzyme
does not require replacement
however.
193.
A.
Covalent modification would not
include
changes of ions.
Phosphorylation/dephosphoryla-
tion is often used as a means of regulation
of
activity of various enzymes.
Sulfation/desulfation
is seldom if ever employed.
194.
B.
The response of most enzymes to
being
boiled in aqueous solution is
substantially
decreased activity as a result of enzyme
denatura-
tion. (Remember that enzymes are proteins
in
general.) More moderate increase in
temperature
increases the activity of an
enzyme.
195.
B.
The number of possible isomers is four.
Note
that positions 3 and 4 are chiral and thus
may
have the hydroxyl group on either side. Thus
2
2 = 4.
196.
B.
Although there appear at first glance to
be
three chiral centers, this is not so; the
number 3
carbon is not attached to four nonidentical
groups.
Thus only four isomers appear to be possible,
but
it can be seen that two of these are identical
and
thus there are two optically active isomers
and
one optically inactive isomer.
197.
B.
There are two chiral centers.
198.
B.
Ribose is found in RNA, contributing to
the
name, ribonucleic acid. Deoxyribose is found
in
DNA.
199.
C.
As seen in the explanation for question
196,
there are only two chiral centers (carbons 2
and 4).
200.
B.
DNA is the primary source of information.
It
is usually considered that DNA directs the
synthe-
sis of RNA and that RNA directs the synthesis
of
protein. DNA also directs its own replication.
In
some cases (for example the retroviruses),
RNA
can direct the synthesis of DNA.
201.
C.
RNA directs the synthesis of protein
(see
above) and three nucleotide bases are required
to
code for each amino acid.
202.
B.
Paired strands of DNA are found in the
chro-
mosomes of higher animals.
203.
A.
None of the cells will have only DNA
con-
taining deuterium. Each cell will have two
strands
of DNA for each chromosome, and one strand
of
each pair will contain deuterium.
204.
D.
As stated above, DNA is required to code
for
RNA and RNA is required to code for
protein.
The enzymes that actually carry out the
biosyn-
thesis are protein. (It might be argued that
DNA is
not required, but ultimately DNA is required
for
RNA synthesis.)
205.
A.
This study investigated the response of
anti-
body produced by a host against the protein of
the
virus inducing tumor. Statements C and D are
con-
tradicted by the evidence. There is no
information
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