CELLS-Cell division

Question 1

what are chromosomes made up of?

Answer 1

up of coiled threads of DNA and proteins

Question 2

for DNA to condense it has to be packaged, this is achieved using what type of positively charged protein?

Answer 2

Histones

Question 3

DNA winds arounds the histones to form?

Answer 3

nucleosomes

Question 4

what are the three stages of the cell cycle?

Answer 4

1.interphase(G0,G1,S and G2)
2.mitosis
3.cytokinesis

Question 5

When chromosomes are coiled and condensed they can be photographed to produce a?

Answer 5

karyotype

Question 6

during interphase describe what happens during G1?

Answer 6

cells increase in size, produce RNA and synthesize proteins. and control checkpoint
-The p53 gene is important in regulating this phase. It triggers the two main checkpoints in the cell cycle and is known as the tumour suppressor gene.

Question 7

during interphase describe what happens during G0?

Answer 7

There are times when a cell will leave the cycle and quit dividing. This may be a temporary resting period
-Here cells may undergo apoptosis, differentiation or senescence. The length of time spent in G0 varies depending on the cell type.

Question 8

during interphase describe what happens during S phase?

Answer 8

Synthesis phase-DNA replication takes place

Question 9

during interphase describe what happens during G2?

Answer 9

the cell will continue to grow and produce new proteins required for cell division. at the end of this gap there is another control checkpoint to determine if the cell can now proceed to enter Mitosis and divide

Question 10

There are two checkpoints during the mitosis phase when are there?

Answer 10

-At the beginning of mitosis a checkpoint chemical triggers the condensation of chromatin into chromosomes
-Halfway through the cycle the metaphase checkpoint ensures the cell is ready to undergo nuclear division

Question 11

what does apoptosis mean?

Answer 11

Apoptosis is a process of programmed cell death that occurs in multicellular organisms

Question 12

what does senescence mean?

Answer 12

senescence is a process by which a cell ages and permanently stops dividing but does not die.

Question 13

give three points of the importance of mitosis?

Answer 13

-asexual reproduction
-growth
-repair

Question 14

describe what happens during prophase?

Answer 14

-chromosomes coil and condense
-each replicated chromosome is seen to consist of 2 chromatids and joined at the centromere
-The centriole replicates and two new daughter centrioles move to opposite poles of the cell and spindles start to form.
-Spindles are made from protein molecules called microtubules.

Question 15

Describe what happens during metaphase?

Answer 15

-The nuclear membrane breaks down.
-Chromosomes align along the equator of the cell.
-Chromosomes are attached to the spindle fibres via the centromeres.

Question 16

Describe what happens during Anaphase?

Answer 16

-Centromeres of each chromatid separate
-Each sister chromatid is pulled along a spindle to one of the poles of the cell.

Question 17

Describe what happens during Telophase?

Answer 17

Early Telophase
-Chromatids reach the poles of the cell and are now known as chromosomes.
-The nuclear envelope begins to reform and the cytoplasm to divide.
Late Telophase
-Chromosomes start to decondense.
-Nuclear membranes and nucleoli are fully reformed and centrioles are present again.
-Division of the cytoplasm continues until 2 identical cells are formed.

Question 18

describe what happens during cytokinesis?

Answer 18

-In animal cells the plasma membrane folds inwards as the cleavage furrow forms pinching the cell in two.

Question 19

describe what happens during cytokinesis? (for plants)

Answer 19

-Vesicles from the
Golgi apparatus a line
along the centre of the
cell.
-They fuse together and forming a cell plate.
Material to form the cell wall collects as the vesicles fuse forming a new cell wall.
-The cell plate enlarges until its surrounding membrane fuses with the plasma membrane along the perimeter of the cell.

Question 20

what is a mutation?

Answer 20

a random change to the base sequence of DNA

Question 21

what are the two types of mutations?

Answer 21

-substitution
-deletion

Question 22

what is the most common cause of hereditary breast cancer?

Answer 22

is an inherited mutation in theBRCA1orBRCA2gene.

Question 23

what are the two tumour types?

Answer 23

-Benign
-Malignant

Question 24

Describe a malignant tumour?

Answer 24

grows quickly, will invade other tissues and can break off and spread around the body causing tumours in other organs (metastasis).

Question 25

Describe a Benign tumour?

Answer 25

grows slowly and is kept in one place. They do not invade other tissues. These are not usually life threatening.

Question 26

name a couple cancer treatments?

Answer 26

-immunotherapy
-surgery
-chemotherapy
-radiotherapy
-drugs

Question 27

how does chemotherapy work?

Answer 27

Chemotherapy prevents the synthesis of enzymes required for DNA replication. This stops the cell cycle before the S phase as it cannot take place. If DNA cannot be replicated cells will not be able to divide.

Question 28

how does radiotherapy work?

Answer 28

Radiotherapy and some chemotherapy drugs can damage DNA, if DNA is damaged the cell will not pass the check points in S phase. This will force the cell to kill itself (apoptosis). Cells will not divide/mitosis is prevented

Question 29

how does drugs work to help treat cancer?

Answer 29

Drugs which prevent spindle fibres from forming will prevent mitosis as one cell will contain double the DNA and one cell will contain no DNA. This prevents the cells from functioning or dividing again.