BI203 Lecture 23: The Cell Cycle - Anaphase and Meiosis (Slides 51 - 66)

Question 1

___ ___ ___ (APC) - A ubiquitin ligase that induces progression from metaphase to anaphase.

Answer 1

Anaphase Promoting Complex (APC)

Question 2

At the ___ ___ ___, 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.

Answer 2

spindle assembly checkpoint

Question 3

At the spindle assembly checkpoint, progression to anaphase is mediated by activation of ___/___ ubiquitin ligase which is phosphorylated by Cdk1/cyclin B.

The presence of even one unaligned chromosome is sufficient to prevent activation of the ___/___.

Answer 3

APC/C

Question 4

At the spindle assembly checkpoint, progression to anaphase is mediated by activation of APC/C ubiquitin ligase which is phosphorylated by ___/___ ___.

The presence of even one unaligned chromosome is sufficient to prevent activation of the APC/C.

Answer 4

Cdk1/cyclin B

Question 5

Unattached kinetochores lead to the assembly of the ___ ___ ___ (MCC), which inhibits APC/C.

Once all chromosomes are aligned on the spindle, the ___ ___ (MCC) no longer forms and APC/C is activated.

Answer 5

Mitotic Checkpoint Complex (MCC)

Question 6

___/___ proteins inhibit APC activity.

___/___ are activated by kinetochores which are unattached to the mitotic spindle.

Attachment of all kinetochores to the mitotic spindle inactivates ___/___.

Answer 6

Mad/Bub

Question 7

___ degrades cohesin, which breaks the link between sister chromatids, allowing them to segregate and move to opposite spindle poles (allows Anaphase to occur).

Answer 7

separase

Question 8

When APC/C is active, it ubiquitylates ___, thus activating ___ to go ahead and degrade cohesins.

Answer 8

securin, separases

Question 9

When APC/C is active, it also ubiquitylates ___ ___, inactivating ___ in the process.

This leads to:
Reformation of nuclear envelope
Chromatin decondensation
Reformation of Golgi
Restructuring of MT cytoskeleton

Answer 9

cyclin B, Cdk1

Question 10

___ usually starts shortly after anaphase starts and is triggered by inactivation of Cdk1.

Answer 10

cytokinesis

Question 11

Cytokinesis usually starts shortly after anaphase starts and is triggered by inactivation of ___.

Answer 11

Cdk1

Question 12

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 ___.

Answer 12

contractile ring, two

Question 13

___ is a specialized cell cycle that reduces the chromosome number by half, resulting in four haploid daughter cells called gametes or germ cells (sperm and egg).

Answer 13

meiosis

Question 14

Meiosis is a specialized cell cycle that reduces the chromosome number by ___, resulting in ___ ___ daughter cells called gametes or germ cells (sperm and egg).

Answer 14

half, four haploid

Question 15

Genetic recombination between homologous chromosomes occurs at high rates during ___ ___ of meiosis.

Answer 15

prophase 1

Question 16

Prophase 1 has ___ stages.

Answer 16

5

Question 17

The 5 stages of Prophase 1:

Answer 17

leptotene, zygotene, pachytene, diplotene, and diakinesis

Question 18

___ - The highly conserved endonuclease Spo11 induces double-strand breaks.

Answer 18

leptotene

Question 19

___ - Close association of homologous chromosomes (synapsis) begins.

Answer 19

zygotene

Question 20

___ - Completion of recombination, leaving the chromosomes linked at sites of crossing over (chiasmata).

Answer 20

pachytene

Question 21

___ - The synapto-nemal complex disappears, except at the chiasmata.

Answer 21

diplotene

Question 22

___ - Each chromosome pair (a bivalent) consists of four chromatids.

Answer 22

diakinesis

Question 23

___ ___ - 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.

Answer 23

metaphase I

Question 24

___ ___ - The chiasmata are disrupted and homologous chromosomes separate; sister chromatids remain attached.

Answer 24

anaphase I

Question 25

Meiosis II starts immediately after ___, usually before the chromosomes have fully decondensed.

Answer 25

cytokinesis

Question 26

___ ___ resembles mitosis.

Answer 26

meiosis II

Question 27

Telophase II produces one gamete and a ___ ___ ___.

Answer 27

second polar body

Question 28

Cell division after meiosis I is asymmetric, resulting in a ___ ___ ___ and an oocyte that retains its large size.

Answer 28

small polar body

Question 29

The oocyte enters meiosis II without having re-formed a nucleus or ___ its chromosomes.

Most vertebrate oocytes are arrested again at metaphase II, until fertilization.

Answer 29

decondensed

Question 30

Binding of a sperm to its receptor signals an increase in ___ levels in the egg cytoplasm which signals the completion of meiosis.

Answer 30

Ca2+

Question 31

After completion of meiosis, the fertilized egg (___) contains two haploid nuclei (___), one derived from each parent.

Answer 31

zygote, pronuclei

Question 32

The two pronuclei replicate their DNA as they migrate toward each other.

As they meet, the zygote enters ___ ___ of the first mitotic division.

Completion of mitosis then gives rise to two embryonic cells, each containing a new ___ genome.

Answer 32

M phase, diploid