cell cycle

Question 1

Describe the prophase stage

Answer 1

Prophase
DNA condenses into
chromosomes each consisting of two sister chromatids.
Nuclear membrane breaks down;
spindle microtubules extend from the MTOC by polymerisation and attach to
chromosomes via their kinetochores in the centromere region.

Question 2

Describe the metaphase stage

Answer 2

Metaphase
chromosomes are aligned at the metaphase plate (equator of the spindle).

Question 3

Describe the anaphase stage

Answer 3

Anaphase
As spindle microtubules shorten
by depolymerisation, sister chromatids are separated, and the chromosomes are pulled to opposite poles.

Question 4

Describe the telophase stage

Answer 4

Telophase
the chromosomes decondense
and nuclear membranes are formed around them.

Question 5

What are the two main stages of the cell cycle

Answer 5

Interphase and the mitotic phase

Question 6

What does the interphase stage involve

Answer 6

Interphase involves growth and DNA
synthesis including
- G1, a growth phase
- S phase, during which the DNA is replicated
- G2, a further growth phase.

Question 7

What does the mitotic phase involve?

Answer 7

Mitotic phase involves mitosis (which is prophase, metaphase, anaphase, telophase) and cytokinesis.

Question 8

In mitosis what separates the chromosome material? How does this happen?

Answer 8

In mitosis the chromosomal material is
separated by the spindle microtubules.

Spindle fibres attach to the chromosomes, they radiate either from the centrosome or the microtubule organising centre (MTOC), the spindle fibres contract and shorten which leads to the spindle microtubules separating the homologous chromosomes.

This is followed by cytokinesis, in which the cytoplasm is separated into two daughter cells.