3.8 The cell cycle

Question 1

What are the 3 stages of the cell cycle called

Answer 1

Interphase: Occupies most of the cell cycle, called the resting phase because no division takes place

Nuclear division: When the nucleus divides either into two (mitosis) or four (meiosis)

Cytokinesis: Division of the cytoplasm, which follows nuclear division and the cytoplasm divides to make two new cells (mitosis) or 4 new cells (meiosis)

Question 2

How long is the complete cell cycle and what percentage of this is interphase

Answer 2

It takes around 24 hours

90% of it is interphase

Question 3

What is cancer, how does a tumour develop

Answer 3

.Uncontrolled growth and division of cells

A group of diseases caused by a growth disorder in cells.
When there is damage to the genes that regulate mitosis and the cell cycle

So as a result a group of abnormal cells (a tumour) develops.

Question 4

How can a tumour become malignant

Answer 4

Malignant is cancerous, whilst benign isn’t, and doesn’t invade organs or tissues as the group of cells are held together in a membrane.

It becomes cancerous if the tumour changes from benign to malignant

Question 5

Why do cells divide by mitosis

3 reasons

Answer 5

. Growth: Increase the size of a tissue during development

. Repair: Replace dead and worn out cells

. Asexual reproduction: It produces an identical copy of the parent cell

Question 6

What can the rate of mitosis be affected by

How do mutations impact it

Answer 6

The environment of the cell,

Two types of gene: mutations in one of these genes results in uncontrolled mitosis

Mutant cells are structurally and functionally different from normal cells, and most mutated cells die.
However any that survive can form clones of themselves and form tumours

Question 7

What is the difference between malignant and benign tumours

Answer 7

. Malignant tumours grow rapidly, are less compact, and are more likely to be life threatening

. Benign tumours grow more slowly, are more compact, and are less likely to be life threatening

Question 8

How do drugs used to treat cancer (chemotherapy) work?

Answer 8

It involves killing dividing cells by blocking parts of the cell cycle, so it is disrupted. These drugs disrupt the cell cycle by:

. Preventing DNA from replicating
. Inhibiting the metaphase stage of mitosis by interfering with the spindle fibre formation

Question 9

What is a problem with chemo / cancer drugs to do with hair loss

but why isn’t it this bad

Answer 9

• They also disrupt the cell cycle of normal cells, eg ones that divide rapidly like hair cells, so they are vulnerable to damage. This explains frequent hair loss.

However, the drugs are more effective against rapidly dividing cells, like cancer cells.