The Medical College - Page 57
Selective protein transport from the maternal
circu-
lation to the rat fetus is thought to occur via
the vis-
ceral yolk sac. The maternal proteins are
transferred
to the yolk sac cavity and then must pass
through the
visceral endoderm, the visceral basement
membrane
(VBM), and the vitelline capillary endothelium
to
reach the fetal blood. Proteins X, Y, and Z
were
injected into a pregnant rat on day 12 of
gestation
and then were localized in the layers of the
visceral
yolk sac at 2 minutes, 6 hours, and 12 hours
follow-
ing injection. The results below demonstrate
where
each protein was localized at the three
postinjection
intervals.
Vitelline
Fetal
Protein
Visceral Endoderm
VBM
Endothelium
Blood
X
2 min.
6 hrs.
12 hrs.
--
Y
2 min., 6 hrs., & 12 hrs.
--
--
--
Z
2 min.
6 hrs.
12 hrs.
12 hrs.
214.
Based on the information given, select the
state-
ment not supported by the information
given
above.
A.
All three proteins were absorbed at
the
same rate by the visceral
endoderm.
B.
The transport of protein X is blocked
by
the visceral basement membrane.
C.
The visceral endoderm appears to block
the
transport of protein Y.
D.
Protein X appears to be transported
through
the visceral endoderm.
The following graph represents an
experiment
designed to measure the rate of collagen
synthesis in
developing chondrocytes. Chondrocytes were
isolated
from developing sterna of chick embryos and
incu-
bated in culture media containing
proline–
3H, a
precur-
sor of collagen. Specimens were fixed after
various
time intervals and prepared for
autoradiography. The
graph represents number of silver grains
counted
(µm/square of organelle).
215.
The following statements are related to
the
information presented. Select the statement
sup-
ported by the information given.
A.
The radioactive label found in the
rough
endoplasmic reticulum is
transferred
directly into the extracellular
collagen
without passing through the Golgi
com-
plex.
B.
Radioactive isotope is incorporated
into
the extracellular collagen within 2
hours.
C.
Collagen is a highly stable molecule and
is
not degraded.
D.
The amount of rough endoplasmic
reticu-
lum in the cell increases during
collagen
synthesis.
216.
Amino acids found in higher animals are
usually:
A.
optically inactive.
B.
of the L-series.
C.
of the D-series.
D.
a racemic mixture.
217.
Carbohydrates found in higher animals (such
as
glucose, fructose, and galactose) are
usually:
A.
optically inactive.
B.
of the L-series.
C.
of the D-series.
D.
a racemic mixture.
218.
D-glucose and L-galactose, both
aldohexoses,
could be said to be:
A.
epimers.
C.
enantiomers.
B.
diastereomers.
D.
A and B.
219.
Foods with the highest number of kcal/g are
the:
A.
carbohydrates.
C.
fats.
B.
proteins.
D.
nucleic acids.
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