Cell Structure and Division - Cell Division - Mitosis

Question 1

What does the cell cycle consist of? [2]

Answer 1

1 - INTERPHASE:

2 - MITOSIS

Question 2

What are the 3 stages of interphase?

Answer 2

a) - GAP PHASE 1 (cell grows and new organelles + proteins are made)
b) - SYNTHESIS (cell replicates it DNA, ready to divide by mitosis)
c) - GAP PHASE 2 (cell keeps growing and proteins needed for cell division are made)

Question 3

What are the 4 division stages of mitosis in order, and what happens in each?

Answer 3

PROPHASE:

• Chromosomes condense - get shorter and fatter
• Tiny bundles of protein called CENTRIOLES start moving to opposite ends of the cell, forming a network of protein fibres called the spindle
• Nuclear envelope breaks down
• Chromosomes lie free in the cytoplasm

METAPHASE:
- Chromosomes (each with 2 chromatids) line up along the middle of the cell and become attached to the spindle by their centromere.

ANAPHASE:

• Centromeres divide, separating each pair of sister chromatids
• Spindles contract, pulling chromatids to opposite poles (ends) of the spindle, centromeres first
• This makes the chromatids appear v-shaped

TELOPHASE:

• Chromatids reach opposite poles on the spindle
• They uncoil - get long and thin and called chromosomes again
• Nuclear envelope forms around each group of chromosomes, so there are now two nuclei
• Cytoplasm divides (cytokinesis) and there are now 2 daughter cells that are genetically identical to original cell and each other.
• Mitosis is finished and each daughter cell starts the interphase part of the cell cycle ready for another round of mitosis.

Question 4

What happens during Interphase?

not the stages

Answer 4

The cell carries out normal functions, but also prepares to divide.

The cell’s DNA is UNRAVELLED and REPLICATED,
to double its genetic content.

The ORGANELLES are also REPLICATED
so it has spare ones,

and its ATP content is INCREASED
(which provides the energy needed for cell division).

Question 5

What are mutations?

Answer 5

MUTATIONS:

Changes in the base sequence of an organism’s DNA.

Question 6

What are mitosis and the cell cycle controlled by?

Answer 6

Genes

Question 7

How do some treatments for cancer work?

[6]

Answer 7

Cancer treatments are designed to control the rate of cell division in tumour cells by disrupting the cell cycle.

This kills the tumour cells.

These treatments don’t distinguish between tumour cells and normal cells, so normal cells undergoing cell division may also be killed.
However, cancer cells divide more frequently so are more likely to be killed.

Some cell cycle targets of cancer treatments include:

G1 (cell growth and protein production):
– CHEMOTHERAPY helps to prevent the synthesis of enzymes needed for DNA replication.
If these aren’t produced, the cell is unable to enter the synthesis (S) phase, disrupting the cell cycle and forcing the cell to kill itself.

S phase (DNA replication):
-- RADIATION and some drugs damage DNA.
At several points in the cell cycle (including just before and during S phase) the DNA in the cell is checked for damage. If severe damage is detected, the cell will kill itself -- preventing further tumour growth.