module 2 - 6.2 mitosis

Question 1

what does the nucleus contain?

Answer 1

chromosomes but as chromatin

Question 2

what is chromatin?

Answer 2

a tangle of unwound chromosomes (DNA) to allow genes to be expressed (e.g. protein synthesis)

Question 3

when is the DNA unwound?

Answer 3

during proteins synthesis

Question 4

what is a chromosome?

Answer 4

a molecule of DNA (linear molecule)

Question 5

what is a centromere made of?

Answer 5

protein

Question 6

why are the chromosomes packaged?

Answer 6

so they can be moved in mitosis

Question 7

what are the chromatids called when they are joined together in one chromosome?

Answer 7

sister chromatids

Question 8

how are there 2 chromatids in the chromosome?

Answer 8

1 line is the original chromosome, the second is its copy of chromosome

Question 9

what are centromeres drawn as when they are drawn more realistically?

Answer 9

2 protein complexes

Question 10

how do you work out the number of chromosomes?

Answer 10

count the number of centromeres (when not draw as individual proteins, only as blobs)

Question 11

what are the stages of mitosis?

Answer 11

prophase
metaphase
anaphase
telophase

Question 12

what happens before prophase?

Answer 12

chromosomes have been replicated/ synthesised during the S phase

Question 13

what are the chromosomes as a diploid number?

Answer 13

2n = 4

Question 14

what are the chromosomes as a haploid number?

Answer 14

n = 2 (1 long chromosome, 1 short chromosome)

Question 15

what does the n stand for in the haploid number of chromosomes?

Answer 15

n = number of different chromosomes based on length/ position of centromere/ bonds

Question 16

what happens during early prophase?

Answer 16

1. chromosomes replicated and condensed, exist as pair of sister chromatids held by centromeres
2. centrioles begin to produce spindle fibres, one centriole moves to opposite pole
3. nuclear envelope begins to disappear
4. spindle fibres grow and bind to centromeres so they can move chromosomes around

Question 17

how is the movement of centrioles special?

Answer 17

movement of centrioles happens in ALL ANIMALS but only in SOME PLANTS

Question 18

what happens during late prophase?

Answer 18

1. nuclear envelope nearly digested/disappeared
2. spindle fibres bind to centromeres and start to move chromosomes around ready for metaphase checkpoint

Question 19

what happens during metaphase and the metaphase checkpoint?

Answer 19

1. spindle fibres move the chromosomes so
   they line up on equator of cell called METAPHASE PLATE (meet in the middle)
2. cell only proceeds to anaphase if conditions of metaphase checkpoint are met

Question 20

what are the conditions of the metaphase checkpoint that need to be met?

Answer 20

• all chromosomes attached to a spindle fibre
• all chromosomes on the metaphase plate

Question 21

what happens during anaphase?

Answer 21

1. spindle fibres contract and pull apart sister chromatids, so they’re called chromosomes again
2. chromosomes pulled to poles of the cell, the ‘arms’ of each chromosome trail behind as they are pulled through the cytoplasm

Question 22

what happens during telophase?

Answer 22

• start of cleavage furrow
• cytoskeleton begins to separate the cytoplasm and pull into plasma membrane
• cell still a single cell but with 2 nuclei, cell nucleus is a copy of original cells
• mitosis is finished

Question 23

what is cytokinesis?

Answer 23

last stage of ‘mitotic phase’

Question 24

what happens during cytokinesis within animal cells?

Answer 24

• cytoskeleton pulls the plasma membrane into the cleavage furrow
• cells separate forming 2 daughter cells
• chromosomes unpackage to form CHROMATIN
• cell enters G1

Question 25

what happens during cytokinesis in plants?

Answer 25

• vesicles line up on metaphase plate and fuse to form 2 separate plasma membranes
• on cell plates, cell wall forms for EACH cell so 2 cell walls form
• 2 daughter cells will grow during G1