Mitosis And Meiosis

Question 1

Where are Astral microtubules and what are their function?

Answer 1

Extend from spindle poles to cell cortex

ORIENT spindle with axis of cell division

Question 2

Where are kinetochore microtubles located and what is there function?

Answer 2

Link spindle poles to kinetochores on sister chromatic pairs

Transport newly separated chromosomes to respective poles.

Question 3

Where are polar microtubles located and what is their function?

Answer 3

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

Question 4

What causes asters to separate and move to opposite sides of the nucleus?

Answer 4

The action of Kinesin-5 motors

Question 5

Where do kinetochores assemble?

Answer 5

On regions of DNA marked by H3 histone variant CENP-A.

Question 6

What end of microtuble is connected to the kinectochore?

Answer 6

The positive end

Question 7

What is congression?

Answer 7

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.

Question 8

Features of the shortening side in congression?

Answer 8

Microtubules disassemble

Shortening is enhanced by kinesin-13

Dynein-dynactin complex moves chromosomes towards pole.

Question 9

Features of the lengthening side during congression?

Answer 9

Kinesin-7 holds chromosome onto growing microtubule

Kinesin-4 pulls chromosome towards center of spindle.

Question 10

What two mechanisms ensure chromosomes are bi-oriented?

Answer 10

1. Tension is generated by attachment to opposite poles
2. The spindle assembly checkpoint, which stops the progression into anaphase until tension is present in all kinetochores.

Question 11

What structure links trhe kinetochore to the microtubule?

Answer 11

The Ndc80.

Question 12

What is the mechanism of Ndc80 linkage?

Answer 12

1. Function is regulated by Chromosomal passenger complex (CPC)
   
   1. CPC contains protein kinase Aurora B
      
      1. ​Aurora B phosphorylates multple proteins
2. When phosphorylated, Ndc80 is less tightly attached to microtubule
   
   1. Phosphorylation is unstable due to presence of phosphatase
3. When tension moves kinetochores away from CPC, Aurora B no longer phosphorylates, resulting in Ndc80 clamping down on the microtubule.

Question 13

How does the spindle assembly checkpoint function?

Answer 13

Signaling circuitry that stops cell cycle from entering anaphase until tension is present in all kinetocores.

Question 14

Steps of Anaphase

Answer 14

• 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)

Question 15

Steps of Telophase

Answer 15

• Nuclear envelope reforms
• Chromosomes decondense
• Contractile ring assembles
  
  • Formed from actin and myosin
  • Placement mediated by CPC

Question 16

Steps in cytokinesis?

Answer 16

• actin-myosin filaments contract
  
  • pulls plasma membrane inward
• cell pinch in half to form two daughter cells
  
  • bridge broken and plasma membrane reseals

Question 17

What does meiosis result in?

Answer 17

Haploid germ cells

Question 18

What occurs in meiosis?

Answer 18

• DNA replication followed by two consecutive chromosomes segregation phases.
• 1 diploid cell becomes 4 haploid cells

Question 19

Pre-meiotic cell (#n)?

Answer 19

2n

Question 20

After chromosomes replicated (#n)?

Answer 20

4n

Question 21

After anaphase 1 (#n)?

Answer 21

2 cells each 2n

Question 22

After meiosis 2? (#n)?

Answer 22

4 cells each 1n

Question 23

Meiosis 1 steps

Answer 23

• 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

Question 24

5 stages of prophase 1 in meiosis 1

Answer 24

• LZPDD
• Leptotene - ball
• Zytogene - separated
• Pachytene - crossover events
• Diplotene - intertwined
• Diakinesis - break apart

Question 25

Differences between Mitosis and Meiosis?

Answer 25

• 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

Question 26

Sites of homologous chromosome linkage?

Answer 26

• Chiasmata (singular chiasma)
  
  • They hold homologous chromosomes together.

Question 27

Oocyte Meiosis?

Answer 27

• 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