Mitosis And Meiosis Flashcards
Where are Astral microtubules and what are their function?
Extend from spindle poles to cell cortex
ORIENT spindle with axis of cell division
Where are kinetochore microtubles located and what is there function?
Link spindle poles to kinetochores on sister chromatic pairs
Transport newly separated chromosomes to respective poles.
Where are polar microtubles located and what is their function?
Extend from each spindle poles body towards opposite one.
Push apart duplicated centrosomes during prophase
Maintain structure of spindle
Push spindle poles apart in anaphase B
What causes asters to separate and move to opposite sides of the nucleus?
The action of Kinesin-5 motors
Where do kinetochores assemble?
On regions of DNA marked by H3 histone variant CENP-A.
What end of microtuble is connected to the kinectochore?
The positive end
What is congression?
It is the moving to the center that occurs when a kinetochore is bi-oriented (connected to both spindles) and under tension moves to the center.
Features of the shortening side in congression?
Microtubules disassemble
Shortening is enhanced by kinesin-13
Dynein-dynactin complex moves chromosomes towards pole.
Features of the lengthening side during congression?
Kinesin-7 holds chromosome onto growing microtubule
Kinesin-4 pulls chromosome towards center of spindle.
What two mechanisms ensure chromosomes are bi-oriented?
- Tension is generated by attachment to opposite poles
- The spindle assembly checkpoint, which stops the progression into anaphase until tension is present in all kinetochores.
What structure links trhe kinetochore to the microtubule?
The Ndc80.
What is the mechanism of Ndc80 linkage?
- Function is regulated by Chromosomal passenger complex (CPC)
- CPC contains protein kinase Aurora B
- Aurora B phosphorylates multple proteins
- CPC contains protein kinase Aurora B
- When phosphorylated, Ndc80 is less tightly attached to microtubule
- Phosphorylation is unstable due to presence of phosphatase
- When tension moves kinetochores away from CPC, Aurora B no longer phosphorylates, resulting in Ndc80 clamping down on the microtubule.
How does the spindle assembly checkpoint function?
Signaling circuitry that stops cell cycle from entering anaphase until tension is present in all kinetocores.
Steps of Anaphase
- Induced by activation of anaphase-promoting complex/cyclosome (APC/C)
- Cohesins degrade
- Sister chromatids separate and move to opposite poles (anaphase A)
- Spindle poles move farther apart (Anaphase B)
Steps of Telophase
- Nuclear envelope reforms
- Chromosomes decondense
- Contractile ring assembles
- Formed from actin and myosin
- Placement mediated by CPC
Steps in cytokinesis?
- actin-myosin filaments contract
- pulls plasma membrane inward
- cell pinch in half to form two daughter cells
- bridge broken and plasma membrane reseals
What does meiosis result in?
Haploid germ cells
What occurs in meiosis?
- DNA replication followed by two consecutive chromosomes segregation phases.
- 1 diploid cell becomes 4 haploid cells
Pre-meiotic cell (#n)?
2n
After chromosomes replicated (#n)?
4n
After anaphase 1 (#n)?
2 cells each 2n
After meiosis 2? (#n)?
4 cells each 1n
Meiosis 1 steps
- Initiates after S phase completed
- Extended prophase 1 with 5 stages based on chromosome morphology
- Homologous chromosomes segregate
- Pair with one another
- Segregate to different daughter cells
- Sister chromatids remain together
- Results in daughter cells containing single member of each chromosome pair
5 stages of prophase 1 in meiosis 1
- LZPDD
- Leptotene - ball
- Zytogene - separated
- Pachytene - crossover events
- Diplotene - intertwined
- Diakinesis - break apart
Differences between Mitosis and Meiosis?
- Meiosis
- has crossover events
- 2 cell divisions: Generates 4 haploid cells
- Cohesins lost from chromosome arms by end of meiosis 1, but those at kinetochores remain until anaphase 2
- full synapsis of homologous chromosomes in prophase
- centromeres divide at anaphase 2 not 1.
- Mitosis
- All cohesins lost by start of anaphase
- Same as Meiosis 2
- No pairing of homologous chromosomes in prophase
Sites of homologous chromosome linkage?
- Chiasmata (singular chiasma)
- They hold homologous chromosomes together.
Oocyte Meiosis?
- Oocytes arrest at diplotene stage
- Chromosomes decondense and are transcribed
- Cell gets BIG
- Resume meiosis in response to hormonal stimulation
- Cell division following meiosis 1 asymmetric
- Produces small polar body and large oocyte
- Arrest in metaphase 2 until fertilization or degradation.
- Fertilization
- Fertilized egg completes meiosis 2
- Second polar body forms
- DNA synthesis and mitosis begins
