Cell Cycle and Mitosis

Question 1

G2 Phase

What happens?

Answer 1

• Centrosomes duplicate
• Nuclear Envelope encloses the nucleus still
• Chromosomes are not condensed yet and are still in the form of chromatin

Question 2

Prophase

Chromosomes? Spindle Apparatus? Nuclear Envelope?

Answer 2

• Chromsomes condense and can now be visibly seen
• Mitotic spindle begins to form made of centrosomes and microtubules connecting them
• Centrosomes move away from each other
• Nuclear Envelope is still present

Question 3

Prometaphase

Chromosomes? Spindle Apparatus? Nuclear Envelope?

Answer 3

• Chromosomes are fully condensed
• Some microtubules attach to the kinetochores, structures formed at the centromere of each chromatid
• Nuclear envelope fragments

Question 4

Metaphase

Chromosomes? Spindle Apparatus? Nuclear Envelope?

Answer 4

• All chromosomes go to the metaphase plate
• Centrosomes are at opposite poles of the cell
• Each chromosomes is connected to each centrosome at the kinetochore by a microtubule
• No nuclear envelope has formed

Question 5

Anaphase

Chromosomes? Spindle Apparatus? Nuclear Envelope?

Answer 5

• Each chromatid becomes an independent chromosome
• The separated chromosomes move toward opposite poles of the cell
• The two ends of the cell have identical chromosomes
• No nuclear envelope has formed

Question 6

Telophase

Chromosomes? Spindle Apparatus? Nuclear Envelope?

Answer 6

• Chromosomes become less condensed
• Microtubules dissapear and cleavage separates the two daughter cells
• Nuclear envelopes form around each daughter cells respective chromosomes

Question 7

Cytokinesis

How is it different in animal and plant cells?

Answer 7

In animal cells, cytokinesis occurs by a process known as cleavage where a cleavage furrow splits the cell.
In plant cells, cytokinesis occurs through vesicles forming a cell plate in the middle of the cell.

Question 8

What did this experiment conclude about chromosome movement in anaphase?

Gary Borisy and colleagues at the University of Wisconsin wanted to determine whether kinetochore microtubules depolymerize at the kinetochore end or the pole end as chromosomes move toward the poles during mitosis.

Answer 8

This experiment supported the hypothesis that spindle fibers shortened at the kinetochore ends and not the spindle pole ends. Also, this meant that chromsomes were walked towards the poles by motor proteins, depolymerizing the microtubule and releasing tubulin subunits as it went along.

Question 9

How can mutations in the spindle apparatus lead to developmental disorders?

How many genes for each? (TWO DISORDERS)

Answer 9

Spindle defects are associated with brain disorders and cancer
- Microcephaly (small brain, stru turally normal but reduced number of cortical neurons)
- Lissencephaly (small brain, smooth surface)

Microcephaly is related to 9 genes that produce proteins localized to centrosomes
Lissencephaly is related to the Lis 1 gene which produces a protein that stabilizes the microtubule/dynein complex.

Question 10

How do anti-cancer drugs work to stop cancer cells from uncontrolled cell division?

Answer 10

Anti-cancer drugs normally target topoisomerase to prevent uncontrolled cell division. They can also halt cells in certain parts of interphase.

Question 11

What portion of the cell cycle is Interphase and what happens in each part.

Answer 11

Interphase accounts for aboput 90% of the cell cycle
1. In G1, there is synthesis of macromlolecules and cytoplasmic organells
2. In the S phase, DNA is replicated
3. In G2, there is additional growth