cell division

Question 1

what are the 3 phases interphase is split into

Answer 1

G1, S, G2

Question 2

what occurs at interphase G1?

Answer 2

• growth phase
• preparations (duplicating organelles, growing in size & making proteins) are made to ensure the cell is ready to go into S phase

Question 3

what occurs in S and G2 phase

Answer 3

S phase::
-now no going back
-also called the synthesis phase because this is where DNA synthesis occurs
- DNA replicates- more important sequences are replicated first.
-each chromosome consist of a pair of sister chromatids
G2 phase::
-cell grows in prep for mitosis

Question 4

where does exiting of the cell cycle occur

Answer 4

• occurs early in G1 phase- cells can either continue in the cell cycle or enter the G0 phase (exiting the cell cycle)

Question 5

what do cells do in the G0 phase

Answer 5

• cells in the G0 phase may differentiate, die or enter senescence (where they stop dividing)

Question 6

in what part of the cell cycle is DNA replicated

Answer 6

the S phase

… the G2 phase is where the cell is getting prepared to double

Question 7

what are the 3 things mitosis is used for?

Answer 7

growth, tissue repair, wound repair

Question 8

why is mitosis relevant for tissue repair?

Answer 8

• mitosis can produce a genetically identical copy.

- the new cell is able to take over the cell that was lost as it contains all the same genes- e.g repair of skin

Question 9

why is mitosis relevant for wound repair

Answer 9

a wound stimulates the action of white blood cells, platelets and growth factors.
these cause cells to undergo mitosis to repair damaged tissues/ blood vessels
- ensures for fast wound recovery

Question 10

why is mitosis relevant for growth

Answer 10

• allows for a growth of a foetus, cells duplicate

- all multicellular organisms grow by producing genetically identical cells

Question 11

what do bacteria reproduce asexually by?

Answer 11

via binary fission

Question 12

what type of offspring does asexual reproduction result in?

Answer 12

genetically identical offspring

Question 13

when can damage to DNA occur

Answer 13

during DNA replication in interphase (s phase)

Question 14

why is the DNA replication phase ( S phase) kept short

Answer 14

since exposed bases are more susceptible to mutation

Question 15

what do cell cycle checkpoints do?

Answer 15

• when mutation occurs damaged DNA id detected and repaired
• makes sure DNA is replicated once in each cycle
• also checks cell division and that its not going too fast as tumours and cancer can then form
• ensures the cell cycle goes in one direction or sections could occur twice

Question 16

what are cell checkpoints

Answer 16

-times in the cell cycle where chemical events occur to regulate division

Question 17

what happens at the G1/S checkpoint (restriction point)

Answer 17

during the G1 phase a chemical can trigger a cell to leave the cell cycle and enter G0- makes sure there are not too many cells or not too few cells

Question 18

what happens at the G1 checkpoint

Answer 18

checks cell is ready for S phase ( occurs at the end of G1)

Question 19

what happens at the G2/M checkpoint

Answer 19

• checks and repairs DNA

- makes sure all the DNA has been checked and repaired before the cell enters mitosis

Question 20

what happens at the mitosis checkpoint

Answer 20

• checkpoint in the middle of mitosis

- checks cell is ready to proceed in mitosis

Question 21

what can happen when the genes controlling cell division mutate

Answer 21

-cell division can occur uncontrollably

Question 22

whats a chromosome

Answer 22

a set of genes made from chromatin (genetic material) wrapped around histones

Question 23

where do spindle fibres attach and what do they do

Answer 23

at the centromere and separate the chromosomes

Question 24

whats a chromatid

Answer 24

a copy of a chromosome while attached to a duplicate

Question 25

how many chromosomes does a human (somatic (body)) cell contain

Answer 25

46 chromosomes ( 23 pairs of homologous chromosomes)

Question 26

what does each pair of chromosomes contain

Answer 26

one chromosome from each parent

Question 27

what are many body cells ( haploid or diploid)

Answer 27

diploid

Question 28

what are homologous chromosomes

Answer 28

matching pairs of chromosomes ( 1 paternal 1 maternal) containing the same genes at the same place but may contain different alleles (variants for the gene)

Question 29

what occurs in meiosis one: prophase 1

Answer 29

• nuclear envelope disappears
• homologous chromosomes pair up and chromatids cross over==-crossing over- random chromatin moves from one pair to another (genes will change)

Question 30

what occurs in meiosis one: metaphase 1

Answer 30

• spindle fibres form and reach chromosomes
• pairs of chromosomes line up on the equator
• pairs line up in a random order (paternal and maternal each way)
• this is independent assortment

Question 31

what occurs in meiosis one: anaphase 1

Answer 31

• entire chromosomes=pulled to poles

- homologous pairs= now separated

Question 32

what occurs in meiosis one: telophase 1

Answer 32

• two nuclei reform
• each is haploid
• chromosomes decondense
• cytokinesis follows

Question 33

what occurs in meiosis two: prophase 2

Answer 33

• nuclear envelope disappears
• chromosomes condense
• chromosomes move to poles +s.f form

Question 34

what occurs in meiosis two: metaphase 2

Answer 34

• chromosomes line up in single file at equator
• s.f binds to centromeres
• random arrangement introduces further variation

Question 35

what occurs in meiosis two: anaphase 2

Answer 35

-chromatids= separated and are pulled to poles

Question 36

what occurs in meiosis two: telophase 2

Answer 36

• envelope forms
• chromosomes decondense
• cytokinesis splits to produce 4 haploid cells

Question 37

where is variation introduced in sexual reproduction

Answer 37

-crossing over in prophase 1, independent assortment in metaphase 1, random arrangement in metaphase 2, random selection of gametes that fuse