L13 - Cell Cycle

Question 1

purpose of the cell cycle?

Answer 1

copy entire genome for :
growth
replacement of lost/damaged cells
maintain cell number

Question 2

how do prokaryotes divide

Answer 2

binary fission

Question 3

describe process of prokaryote division

Answer 3

1. DNA is attached to membrane
2. cell enlarges and DNA duplicates
3. septum forms (___|___) in middle of cell with DNA either side
4. cells separate

Question 4

what is unusual about DNA replication and cytokinesis in prokaryotes

Answer 4

they occur at same time - so have to be coordinated

Question 5

describe DNA replication in prokaryotes

Answer 5

1. there is 1 origin of replication
2. helicase catalyses DNA unwinding forming two replication forks at origin (bidirectional)
3. DNA pol works around DNA until the bottom where two circular copies are formed

Question 6

describe prokaryote cytokinesis

Answer 6

1. FtsZ is a protein that forms a ring of protein around the middle of the inner surface of PM
2. this ring contracts
3. PM on each side becomes so close that they fuse
4. two cells

Question 7

do cytokinesis and DNA replication take the same amount of time? (in prokaryotes)

Answer 7

no, DNA replication takes longer

Question 8

how is DNA rep and cytokinesis co ordinated in prokaryotes

Answer 8

cells undergo multifork replication to ensure at least 1 round of replication is completed before cytokinesis

Question 9

what is multifork replication

Answer 9

DNA replication is initiated before previous is completed

Question 10

what are the phases of the Eukaryotic cell cycle (in order)

Answer 10

1. G1
2. S
3. G2
4. mitosis

Question 11

describe what happens in G1

Answer 11

growth phase

doubling of organelles, proteins, enzymes etc

Question 12

what happens in S phase

Answer 12

DNA replication

Question 13

why mustn’t the newly replicated sister chromatids be separated too soon? how are they kept together

Answer 13

would affect attachment of mitotic spindle

hoop of cohesin around the pair held together by kleisin

Question 14

what happens in G2

Answer 14

preparation for mitosis

Question 15

what 3 events mark the beginning of mitosis

Answer 15

1. chromosome condensation
2. nuclear envelope breakdown
3. mitotic spindle formation

Question 16

what is interphase

Answer 16

G1 S G2

Question 17

what happens during prophase

Answer 17

1. chromosome condensation - condensin circles DNA and compresses (C become visible)
2. nuclear envelope breaks down

Question 18

why must the nuclear envelope break down early on in mitosis

Answer 18

so the spindle has access to the chromosomes

Question 19

what happens during metaphase

Answer 19

mitotic spindle formation

chromosomes line up on equator

Question 20

what happens during anaphase

Answer 20

separation of sister chromatids - kleisin cleaved, cohesin ring opens up, spindle attaches and begins shortening

Question 21

what happens during telophase

Answer 21

chromatids separated to either end of cell

Question 22

describe the process of cytokinesis

Answer 22

1. nuclear membrane begins to reform
2. cytoplasm divided in two by contractile ring of actin &myosin 2 filaments
3. membranes pinch from outside in into two cells in middle

Question 23

cell cycle variations : explain how cell cycles vary time wise

Answer 23

1. timing differs between species

2. timing differs due to part of body cell is from eg liver 1 year cycle

Question 24

cell cycle variations : how do cell cycles differ in size

Answer 24

eg somatic cells all same size as they grow after division

embryonic cells divide without growing so cells get smaller with each division

Question 25

cell cycle variations : how do cell cycles differ in nuclear envelope dynamics

Answer 25

multicellular - open mitosis - nuclear envelope breaks down because spindle is outside nucleus unicellular - closed mitosis - NE doesn't break down

Question 26

what is anchorage dependence

Answer 26

cells must be attatched to a surface to be able to divide

Question 27

what is density dependant inhibition

Answer 27

cells stop dividing when they contact eachother (eg fill up a flat surface)

Question 28

how is cell cycle controlled

Answer 28

1. cell cycle engine 2. co ordination (replicated DNA must undergo mitosis before replicating again) 3. checkpoints also anchorage dependence density dependant inhibition

Question 29

explain the position of Restriction point checkpoint and its function

Answer 29

end of G1 before S | decides whether to initiate new cycle

Question 30

explain the position and function of G2 checkpoint

Answer 30

in G2, checks if S phase has been completed

Question 31

explain the location and function of the spindle checkpoint

Answer 31

start of mitosis | ensures spindle is attached to each chromosome

Question 32

explain location of DNA damage checkpoint and its function

Answer 32

throughout cell cycle | if damage detected, cycle paused and fixed

Question 33

what can failure in the DNA damage checkpoint lead to

Answer 33

damaged DNA being replicated - mutation - cancer

Question 34

what can failure in the Restriction point checkpoint lead to

Answer 34

uncontrolled initiation of cell cycles - tumours

Question 35

what can failure in the spindle checkpoint lead to

Answer 35

failure to separate chromosomes equally - aneuploidy/downsyndrome

Question 36

accumulation of what protein will trigger cytokinesis in prokaryotes

Answer 36

FtsZ

Question 37

what proteins ensure sister chromatids aren't separated to early during mitosis and how

Answer 37

cohesin forms a loop held shut by kleisin

Question 38

what protein mediates the centromere

Answer 38

kinetochore

Question 39

what drives the cell cycle

Answer 39

cyclin and cyclin dependant kinase (CDK)

Question 40

what 3 things will halt cell cycle

Answer 40

1. no nutrients 2. damaged DNA 3. chromosomes fail to attach to mitotic spindle

Question 41

what is the cell cycle engine

Answer 41

the protein complex that drives the cell cycle

Question 42

what happens to levels of CDK throughout the cell cycle

Answer 42

remains the same, its the activity that changes

Question 43

what happens to levels of cyclins throughout the cell cycle

Answer 43

rise and fall

Question 44

what phase does cyclin E drive and what is the name of the cyclin involved

Answer 44

G1 into S | G1/S CDK

Question 45

what phase of the cycle does cyclin B drive and what is the name of the cyclin involved

Answer 45

G2 into mitosis (induces NE breakdown) | M CDK