Introduction to Physiology: The Cell and General Physiology

1
(No Transcript)
2
Question 1. Which parameter of microtubule
dynamic instability is dramatically different
during mitosis?
A. Elongation rateB. Elongation time before
catastropheC. Shortening rateD. Probability
of rescue from a catastrophe
3
Answer
D. Probability of rescue from a catastrophe
4
Feedback
Microtubules tend to be shorter in mitosis
because even though they grow a bit more rapidly
than they do during interphase, once they undergo
a catastrophe, they depolymerize completely.
5
Question 2. Which of the following statements
about the spindle checkpoint is untrue?
A. The spindle checkpoint is activated by
kinetochores that lack bound microtubules. B. The
spindle checkpoint is activated by
kinetochore- microtubule attachments that are not
under proper tension.C. The target of the
spindle checkpoint is the protein kinase
BubR1.D. Even a single unattached kinetochore is
capable of sending a signal to activate the
checkpoint and delay entry of the cell into
anaphase.E. Aberrant kinetochore-microtubule
connections are corrected by the action of the
chromosomal passenger complex and Aurora B
protein kinase.
6
Answer
C. The target of the spindle checkpoint is the
protein kinase BubR1.
7
Feedback
The target of the spindle checkpoint is the
auxiliary subunit of the APC/C, Cdc20.
8
Question 3. Sister chromatid separation at
anaphase is triggered by cleavage of two
proteins, Scc1 and
A. separase. B. cohesin. C. Securin. D. SMC1.
E. Aurora B.
9
Answer
C. Securin.
10
Feedback
Destruction of securin by proteasomes activates
separase, which cleaves Scc1. This breaks the
cohesin ring and allows sister chromatids to
separate.
11
Question 4. True or false The position of
cleavage furrows is specified by a cleavage
stimulus that acts upon the cell cortex midway
between spindle poles, regardless of whether
chromosomes are present or not.
A. True B. False
12
Answer
A. True
13
Feedback
Cortical commitment to cleavage results in
production of a self-propagating furrow that can
spread hundreds of micrometers across the surface
of very large cells, such as fertilized eggs.
14
Question 5. Which of the following statements
about cytokinesis is false?
A. Cytokinesis in animal cells involves
constriction of an actin-myosin ring. B. As
cells undergo cytokinesis, constriction of the
equator causes an overall decrease in surface
area.C. In the mammalian testis, cytokinesis is
incomplete and intercellular bridges remain open
linking large numbers of developing sperm
cells.D. During the latter stages of
cytokinesis, constriction and disassembly of the
contractile ring occur at the same time.E. The
final separation of daughter cells at the end of
cytokinesis is known as abscission.
15
Answer
B. As cells undergo cytokinesis, constriction of
the equator causes an overall decrease in
surface area.
16
Feedback
As cells undergo cytokinesis, constriction of the
equator causes an overall increase in surface
area, necessitating the delivery of new membrane
to the cell surface.
17
Question 6. True or false During plant cell
cytokinesis, daughter cells are separated by
constriction of the phragmoplast.
A. True B. False
18
Answer
A. True
19
Feedback
During plant cell cytokinesis, the phragmoplast,
containing anti-parallel microtubules of the
central spindle plus actin filaments and vesicles
derived from the Golgi forms centrally and
gradually expands laterally to make a double disk
abutting the plane of cell cleavage. Cleavage is
accomplished by fusion of the membrane vesicles
coordinated with the laying down of new cell wall.