Cell Cycle (mitosis)

Question 1

Why do we need mitosis?

Answer 1

• growth (unicellular zygote to a multi cellular embryo, constantly growing plants)
  -repair
  -reproduction (some single-celled organisms)

Question 2

3 stages of cell cycle

Answer 2

1)interphase
2)mitosis
3)cytokinesis

Question 3

Interphase

Answer 3

Gap 1 -making of the RNA,enzymes and other proteins required for growth
Synthesis Phase- DNA replicated and each chromosome consists of two chromatids joined via a centromere
Gap 2- continues to grow and checks synthesised DNA for errors. Other preparations such as production of the Tubulin protein which is used to make micro tumbles for spindle fibres

Question 4

Prophase

Answer 4

-chromosomes condense and become visible when stained
-chromosomes consist of 2 sister chromatids joined via centromere
-centromere move to opposite poles of cell and produce spindle fibres
-nuclear envelope breaks down into small vesicles

Question 5

Metaphase

Answer 5

-centrosomes reach poles of cell and spindle fibres are extended
-chromosomes line up along metaphase plate to be equidistant from poles
-spindle fibres reach chromosomes and attach to their centromeres
-each sister chromatid attached to fibre of opposite pole

Question 6

Anaphase

Answer 6

-sister chromatids separate at the centromere (divides in 2)
-spindle fibres shorten
-separated sister chromatids are now called chromosomes and are pulled to opposite poles by spindle fibres

Question 7

Telophase

Answer 7

-chromosomes arrive at poles and begin to decondense
-nuclear envelopes begin to reform around each set of chromosomes to form a nucleus
-spindle fibres breakdown

Question 8

Cytokinesis

Answer 8

-physical separation of a parent cell into 2 genetically identical daughter cells occurring when a nucleus is formed at each pole of a cell

Question 9

Cytokinesis in animals

Answer 9

-cleavage furrow is formed and separates the daughter cell

Question 10

Cytokinesis in plants

Answer 10

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

Question 11

How is cancer caused?

Answer 11

-before a cell divides DNA is checked for mutations and certain chemical signals will start/stop dividing

Cancer is caused by:
-uncontrolled mitosis
-dividing repeatably and uncontrollably forming a tumour
-start when mutation occurs in genes that control cell division
-if mutated gene is one that causes cancer it is referred to as an oncogene
-mutations are common and do not often lead to cancer
Mutations has to occur in correct gene to cause a mutation (greater chances as you get older)

Question 12

What are oncogenes?

Answer 12

Genes that code for proteins that stimulate the transition form one stage of the cell cycle to another. Mutations in these means cell continue the cycle unchecked

Question 13

What are humour suppressor genes?

Answer 13

Genes which produce suppressor proteins that stop the cell cycle. Mutations which inactivate these genes leaves the cell with no brake on the cell cycle

Question 14

What are P53 genes?

Answer 14

Example of a tumour suppressor gene which stops cell cycle by inhibiting enzymes in G1 phase. Which therefore prevents cells from copying DNA
-in cancer cells that lack P53 the cell cannot stop entry or replication so they loose control of the cell cycle
-almost half of people with cancer possess mutated P53 gene

Question 15

Types of carcinogens

Answer 15

1)ionising radiation
2)smoking
3)pollutants
4)chemicals
5)viruses

Question 16

Two types of tumours

Answer 16

Benign- do not spread for their original site and do not cause cancer
Malignant- spread throughout body invading and destroying other tissues causing cancer

Question 17

Steps of a spreading malignant tumour

Answer 17

1)tumour cells secrete chemicals to stimulate blood vessels to grow around the tumour
2)cancer cells detach from the tumour and are transported in the blood
3)a malignant cell squeezes through blood capillary wall
4)cell divides and secondary tumour starts to grow

Question 18

Treating Cancer

Answer 18

-killing dividing cells vis blocking parts of cell cycle
-disrupting cell cycle so it ceases

Chemotherapy:
1) can prevent DNA replicating via inhibiting DNA polymerase enzymes.
2)inhibits the metaphase stage of mitosis by interfering with spindle formation
-side effects also effect cell cycle of normal cells
-chemotherapy works faster on rapidly dividing cells such as cancer but also hair cells