Cell Division

Question 1

Why do we need mitosis?

Answer 1

Growth
Repair
Reproduction (asexual)

Question 2

What are the three stages of the cell cycle?

Answer 2

Interphase
Nuclear division: mitosis
Cell division: cytokinesis

Question 3

What stage of the cell cycle is the longest?

Answer 3

Interphase

Question 4

What happens in the G1phase?

Answer 4

RNA, enzymes and other proteins required for growth are made.

Question 5

What happens in the synthesis phase?

Answer 5

DNA replicates (each chromosome consists of two sister chromatids)

Question 6

What happens in the G2 phase?

Answer 6

Cell continues to grow (energy stores increase) and replicated DNA is checked for any errors which if found are usually repaired.

Question 7

What are the four phases of mitosis?

Answer 7

Prophase
Metaphase
Anaphase
Telophase

Question 8

What happens in prophase?

Answer 8

Nuclear envelope breaks down.
Chromosomes condense (visible when stained.
Chromosomes = identical chromatids joined by centromere.
Centrosomes move to opposite poles.
Spindle fibres emerge from centrosomes.

Question 9

What are spindle fibres made of?

Answer 9

Protein microtubules

Question 10

What happens during metaphase?

Answer 10

Centrosomes reach opposite poles.
Spindle fibres continue to extend.
Chromosomes line up along the metaphase plate.
Spindle fibres reach the chromosomes and attach to the centromeres.
Each sister chromatid is attached to a spindle fibre originating from the opposite poles.

Question 11

What happens during anaphase?

Answer 11

Sister chromatids separate at the centromere (centromere divides in two).
Spindle fibres begin to shorten.
Separated sister chromatids (now called chromosomes again) are pulled to opposite poles by spindle fibres.

Question 12

What happens during telophase?

Answer 12

Chromosomes arrive at opposite poles and begin to decondense.
Nuclear envelope begins to reform around each set of chromosomes to form a nucleus.
Spindle fibres break down.

Question 13

What is cytokinesis?

Answer 13

The physical separation of parent cells into two genetically identical daughter cells.

Question 14

When does cytokinesis occur?

Answer 14

Once a new nucleus has completely reformed at each pole of the parent cell at the end of telophase.

Question 15

What happens during cytokinesis in animals?

Answer 15

A cleavage furrow forms and separates the daughter cells.

Question 16

What happens during cytokinesis in plants?

Answer 16

A cell plate (precursor to new cell wall) forms at the site of the metaphase plate.
Once the cell plate reaches the cell walls of the parent cell new cell walls are produced separating the new daughter cells.

Question 17

What is the cell plate?

Answer 17

Precursor to a new cell wall.

Question 18

What is cancer?

Answer 18

Uncontrolled mitosis - cells divide rapidly and uncontrollably forming a tumour.

Question 19

How does cancer start?

Answer 19

When a mutation occurs in the genes that control cell division.

Question 20

What is an oncogene?

Answer 20

A mutated gene that has the potential to cause cancer.

Question 21

True or false: mutations always lead to cancer.

Answer 21

False
Mutations are common events and most cell mutations are destroyed.

Question 22

What genes control the cell cycle?

Answer 22

Oncogene
Tumour suppressor gene

Question 23

How do oncogenes control the cell cycle?

Answer 23

Code for proteins that stimulate the transition from one stage of the cell cycle to the next.

Question 24

What would mutations in an oncogene cause?

Answer 24

Cell continues the cell cycle unchecked.

Question 25

How do tumour suppressor genes control the cell cycle?

Answer 25

Produce suppressor proteins that stop the cell cycle.

Question 26

What do mutations in the tumour suppressor gene cause?

Answer 26

Inactive these genes leaving the cell with no break on the cell cycle.

Question 27

What is the P53 gene? What does it do during the cell cycle?

Answer 27

A tumour suppressor protein. Stops the cell cycle - inhibits enzymes in the G1/S phase, preventing the cell from copying DNA.

Question 28

In cancer cells what does the lack of P53 genes mean?

Answer 28

Can’t stop entry into S phase + DNA replication therefore cell has lost control of the cell cycle.

Question 29

How many people who have cancer posses a P53 gene?

Answer 29

1/2

Question 30

Give examples of carcinogens

Answer 30

Radiation (UV + X-ray) Smoking Pollutants Chemicals Viruses

Question 31

How does a mutated cell become cancerous?

Answer 31

If it doesn’t undergo early cell death or destroyed.

Question 32

What’s a benign tumour? Does it cause cancer?

Answer 32

Tumour doesn’t spread from orginal site. Doesn’t cause cancer.

Question 33

What’s a malignant tumour? Does it cause cancer?

Answer 33

Tumour spreads through the body, invading and destroying other tissues. Causes cancer.

Question 34

State the steps for the spread of malignant tumours.

Answer 34

1) Tumours cells secrete chemicals to stimulate blood vessels to grow around the tumour. 2) Cancer cells detach from the tumour and are transported into the blood. 3) A malignant cell squeezes through the blood capillary wall. 4) The cell divides - a secondary tumour starts to grow.

Question 35

How can cancer to be treated?

Answer 35

By killing dividing cells by blocking parts of the cell cycle to cease division. Chemotherapy

Question 36

What are the two ways chemotherapy disrupts the cell cycle?

Answer 36

1) Preventing DNA from replicating (inhibits enzymes such as DNA polymerase or DNA helicase) 2) Inhibiting metaphase stage of mitosis by interfering with spindle formation.

Question 37

True or false: side effects of chemotherapy also interfere with cycle of normal cells.

Answer 37

True

Question 38

What type of cells does chemotherapy work fastest on?

Answer 38

Rapidly dividing cells.