Module 9: Introduction To The Cell Cycle

Question 1

What four events can the cell cycle be divided into? (4)
What occurs during these phases? (1+1+0+1)
What is the G-zero phase? (1) What cells are in this phase; which are not? (2)

Answer 1

1. G1 (Gap Phase 1)— cell actively grows, gene expression & new protein synthesis.
2. S-phase (DNA Synthesis Phase)— DNA replication; entire genome replication
3. G2 (Gap Phase 2)
   4.M-phase (Mitosis Phase)— cell division phase; separation of sister chromatids to two daughter cells
   The phase cells enter when they are not dividing. Most cells exist in this phase; stem cells do not.

Question 2

When are cells no longer capable of cell division? (1)

Answer 2

Once they have differentiated from stem cells to specialized cells.

Question 3

What are the subphases of the M-phase? (7)

Answer 3

1. Interphase.
2. Prophase.
3. Prometaphase.
4. Metaphase.
5. Anaphase.
6. Telophase.
7. Cytokinesis.

Question 4

What occurs in interphase? (1)
What does this entail? (2)

Answer 4

Cell prepares for mitosis:
- chromosomes (DNA and associated proteins) are replicated into sister chromatids in S-phase
- centrosomes are duplicated in G1 and S-phase.

Question 5

What occurs in Prophase to the: (4)
- chromosomes
- centrosomes and their function
- nuclear envelope
- endo-membranes of cell

Answer 5

Chromosomes begin to condense; assembly of mitotic spindle begins (centrosomes separate to opposite sides of cell); dissolution of the nuclear envelope; breakdown of endo-membranes of cell into small vesicles.

Question 6

What occurs in the Prometaphase to the: (2+1+1)
- chromosomes
- kinetochore proteins
- chromosomes <—> ____- ends of spindle microtubules

Answer 6

Fully-condensed chromosomes are in process of attaching to fully-formed bipolar microtubule spindle via their centromeres; during attachment, kinetochore proteins assemble at centromeres of chromosomes to mediate association of chromosomes with plus-ends of spindle microtubules

Question 7

What is Metaphase characterized by? (1)
What does the tension that results from forces pulling a duplicated chromosome simultaneously toward both poles cause? (1)

Answer 7

Bipolar attachment— attachment of every chromosome to spindle microtubules from both poles of mitotic spindle.
It causes the chromosomes to aggregate/align in the middle of the mitotic spindle; at the equator of the spindle.

Question 8

What defines Anaphase? (1)
What allows this to occur? (2)

Answer 8

The separation of sister chromatids to opposite poles of spindle.
When all chromosomes have achieved a bipolar attachment to the spindles, a signal releases the association between replicated sister chromatids and they are pulled to opposite poles of spindle.

Question 9

What defines Telophase? (1)
What does this entail for the chromosomes, mitotic spindle, nuclear envelope & endomembrane systems? (3)

Answer 9

Cell reversal of all cellular changes that occurred in prophase.
Chromosomes decondense, mitotic spindle disassembles, nuclear envelope and endomembrane systems reassemble.

Question 10

What is used to observe the phases and what does is target? (2)

Answer 10

Fluorescent dye called DAPI; it targets DNA.

Question 11

What classes of protein regulate the sequences of events in mitosis? Compare them. (2)

Answer 11

CDKs (cyclin-dependant kinases): heterodimeric protein complexes; facilitate regulated phosphorylation.
E3 ubiquitin ligase complexes : target specific proteins for degradation to turn off kinases/ cell cycle inhibtors

Question 12

Kinase activity of CDK complexes are regulated through association with which protein? (1)
What does the activated kinase result in? (1)

Answer 12

Cyclin.
The various cellular processes through the phosphorylation of target proteins.

Question 13

(Slide 8)