Test 4. Lecture 36 Flashcards
“events of M phase”
At the spindle assembly checkpoint, progression to anaphase is mediated by
activation of APC/C ubiquitin ligase which is phosphorylated by Cdk1/cyclin B.
The presence of even one
unaligned chromosome is sufficient to prevent
activation of the APC/C.
Unattached kinetochores lead to the assembly of the ______________, which inhibits APC/C.
Once all chromosomes are aligned on the spindle, the inhibitory complex is no
longer formed and APC/C is activated.
APC/C ubiquitylates cyclin B and securin, which inactivates Cdk1 and separase.
___________, which breaks the link between sister
chromatids, allowing them to segregate and move to opposite spindle poles.
APC/C ubiqumitotic checkpoint
complex (MCC)itin ligase
Separase degrades cohesin
Cytokinesis usually starts shortly after anaphase starts and is triggered by the
inactivation of Cdk1.
• Cytokinesis of yeast and animal cells is mediated by a ____________ of actin
and myosin II filaments that forms beneath the plasma membrane.
Ring formation is activated by Aurora and Polo-like kinases.
• The cell is cleaved in a plane that passes through the metaphase plate.
• Contraction of the actin-myosin filaments pulls the plasma membrane inward,
eventually pinching the cell in half
contractile ring
- During meiosis I, _____________pair with one another
and then segregate to different daughter cells.
Sister chromatids remain together, so the daughter cells contain a single
member of each chromosome pair (two sister chromatids).
homologous chromosomes
- Meiosis II resembles mitosis in that_________________
and segregate to different daughter cells.
The result is four haploid daughter cells; each has only one copy of each
chromosome.
Recombination between homologous chromosomes occurs during
the sister chromatids separate
Prophase I has five stages, based on chromosome morphology:
________________
leptotene, zygotene, pachytene, diplotene, and diakinesis
“meiosis”
1. In __________, the highly conserved endonuclease Spo11 induces
double-strand breaks.
These lead to single-strand regions that invade a homologous
chromosome by complementary base pairing.
- Close association of homologous chromosomes (synapsis) begins
during ___________.
The zipperlike_____________ forms along the length of the
paired chromosomes.
This keeps homologous chromosomes closely associated and aligned.
- Recombination is complete by the end of ___________, leaving the
chromosomes linked at sites of crossing over (chiasmata). - The synaptonemal complex disappears at _______________, except at
the chiasmata.
Each chromosome pair (a bivalent) consists of four chromatids. - ___________ is the transition to metaphase, during which the
chromosomes become fully condensed.
leptotene
zygotene
synaptonemal complex
pachytene
diplotene
Diakinesis
_______________: bivalent chromosomes align on the spindle.
Kinetochores of sister chromatids are oriented in the same
direction; kinetochores of homologous chromosomes are
pointed toward opposite spindle poles.
Microtubules from the same pole of the spindle attach to sister
chromatids, while microtubules from opposite poles attach to
homologous chromosomes.
_____________: the chiasmata are disrupted and homologous
chromosomes separate; sister chromatids remain attached.
Metaphase I
Anaphase I
Meiosis II starts immediately after cytokinesis, usually before the chromosomes
have fully decondensed.
Meiosis II resembles mitosis.
Vertebrate oocytes have been useful models in cell cycle research because they
are large and easy to manipulate in the laboratory.
Meiosis of these oocytes is regulated at two unique points in the cell cycle.
Oocytes can remain arrested in theMeiosis II starts immediately after cytokinesis, usually before the chromosomes
have fully decondensed.
Meiosis II resembles mitosis.
Vertebrate oocytes have been useful models in cell cycle research because they
are large and easy to manipulate in the laboratory.
Meiosis of these oocytes is regulated at two unique points in the cell cycle.
Oocytes can remain arrested in the diplotene stage of meiosis I for long
periods—up to 50 years in humans.
During this arrest, chromosomes decondense and are actively transcribed.
Oocytes grow very large and stockpile materials for early embryonic growth________________ for long
periods—up to 50 years in humans.
During this arrest, chromosomes decondense and are actively transcribed.
Oocytes grow very large and stockpile materials for early embryonic growth.
Meiosis II starts immediately after cytokinesis, usually before the chromosomes
have fully decondensed.
Meiosis II resembles mitosis.
Vertebrate oocytes have been useful models in cell cycle research because they
are large and easy to manipulate in the laboratory.
Meiosis of these oocytes is regulated at two unique points in the cell cycle.
Oocytes can remain arrested in the diplotene stage of meiosis I for long
periods—up to 50 years in humans.
During this arrest, chromosomes decondense and are actively transcribed.
Oocytes grow very large and stockpile materials for early embryonic growth.
Oocytes of most vertebrates resume meiosis in
response to hormonal stimulation and proceed
through meiosis I prior to fertilization.
Cell division after meiosis I is asymmetric,
resulting in a small __________ and an oocyte
that retains its large size.
The oocyte enters meiosis II without having reformed
a nucleus or decondensed its
chromosomes.
Most vertebrate oocytes are ______________, until fertilization
polar body
arrested again at
metaphase II
Meiosis of oocytes is controlled by Cdk1/cyclin B complexes:
• ________________ resulting in progression to
metaphase I.
• Levels of Cdk1/cyclin B determine progression to the next stages.
Hormonal stimulation activates Cdk1/cyclin B,
The factor responsible for \_\_\_\_\_\_\_\_\_\_\_\_\_ was identified in 1971, in the same series of experiments that led to discovery of MPF.
• Cytoplasm from an egg arrested at metaphase II was injected into an early embryo cell, causing it to arrest at metaphase.
metaphase II arrest
Fertilization:
The sperm binds to a _________ the
egg surface and fuses with the egg plasma membrane.
Fertilization mixes paternal and maternal chromosomes and induces
changes in the egg cytoplasm
important for further development.
receptor on
- Binding of a sperm to its receptor signals an increase in Ca2+
levels in the egg cytoplasm, probably from hydrolysis of (PIP2). - Secretory vesicles release materials that coat the egg and block
entry of additional sperm. This ensures a normal diploid embryo. - ___________ also signals completion of meiosis.
- Asymmetric cytokinesis gives rise to a second small polar body. After completion of meiosis, the fertilized egg (______________) contains two haploid nuclei (__________), one derived from each parent.
Increased Ca2
zygote
pronuclei
The pronuclei replicate their DNA as
they migrate toward each other.
• As they meet, the zygote enters M
phase of the first mitotic division.
Chromosomes align on one spindle.
• Completion of mitosis gives rise to
_________________________________________
two embryonic cells, each containing
a new diploid genome
