cell cycle

Question 1

what is the cell cycle?

Answer 1

period of time between birth of cells and its production of daughter cells

Question 2

how long does the cell cycle last?

Answer 2

at least 12 hours

Question 3

what 2 phases does the cell cycle consist of?

Answer 3

interphase and mitotic phase (mitosis)

Question 4

what is interphase?

Answer 4

-interval between the end of mitosis and beginning of the next
-(cell is either resting or performing its specialised work not in mitosis)
-chromosomes aren’t visible (uncoiled)

Question 5

what are cyclins?

Answer 5

cell cycle protein molecules that help fainting the cell cycle →increases/decreases concentration

Question 6

what are the 3 cyclins present in the cell cycle

Answer 6

cyclins:
-E (G1)
-A (S)
-B (G2)

Question 7

what do cyclins do?

Answer 7

cyclins activate and act with cyclin dependant kinases (CDK’s)

Question 8

what happens to cyclins and CDK’s after the cell cycle?

Answer 8

-they are degraded
-residues are taken up by ubiquitin (cytoplasm caretaker protein)

Question 9

what is the G1 phase?

Answer 9

-growth phase→cells respond to growth factors (irreversible)
-makes molecular machinery for another cell cycle

Question 10

when does G1 phase occur?

Answer 10

-between end of mitosis and S phase

Question 11

what is G1 phase controlled by? (cyclin)

Answer 11

cyclin E and CDK’s

Question 12

how long does G1 phase last?

Answer 12

-lasts for less an 2 hours or more than 100 hours

Question 13

What is S phase?

Answer 13

-DNA is replicated

Question 14

when does S phase occur?

Answer 14

-after G1 phase before G2 phase

Question 15

what is S phase controlled by? (cyclin)

Answer 15

cyclin A and CDK’s

Question 16

how long does S phase last

Answer 16

7-8 hours

Question 17

what is G0 phase?

Answer 17

-Contain cells that do not divide but increase in number (quiescent cells)
-cells do not enter S phase

Question 18

what can happen to quiescent cells during G0 phase?

Answer 18

→growth factors can stimulate quiescent cells to leave G0 and re-enter the cell cycle
→proteins encoded by Rb (tumour suppressor proteins) block the cell cycle in G1

Question 19

what is the G2 phase?

Answer 19

-cell prepares for division
-ends with the breakdown of the nuclear membrane and the onset of chromosome coiling

Question 20

when does the G2 phase occur?

Answer 20

-end of S phase and beginning of mitosis

Question 21

what is the G2 phase controlled by? (cyclin)

Answer 21

-cyclin B and CDK’s

Question 22

how long does G2 phase last

Answer 22

2-4 hours

Question 23

what are the 2 routes cells can take after mitosis?

Answer 23

→Enter the cell cycle again
→Enter the G0 phase

Question 24

what 2 things does the mitotic phase include

Answer 24

-mitosis
-cytokinesis

Question 25

what happens at the end of G1 phase?

Answer 25

G1 checkpoint
-cell checks to see if:
→DNA is not damaged
→right proteins are synthesized

Question 26

what happens during prophase?

Answer 26

-chromosomes are first visualized. + splits longitudinally into 2 chromatids at the centromere.
-centrioles are separated to opposite poles by microtubules of the achromatic spindle

Question 27

how long does metaphase last for?

Answer 27

20 minutes

Question 28

how long does prophase last for?

Answer 28

1.5 hours

Question 29

what happens during prometaphase?

Answer 29

-nucleus membrane and nucleolus disappear
-chromosomes entangled in meshwork of microtubules

Question 30

what happens during metaphase?

Answer 30

-chromosomes align at the metaphase plate or equator of the spindle and attach to spindle fibres
-centromere for each chromosome has bilateral disc→kinetochores

Question 31

what do colchicine do?

Answer 31

-stops the cell division at metaphase
-prevents the formation of microtubules of the spindle
-important for karyotyping

Question 32

what happens during anaphase?

Answer 32

-Spindle fibres contract
-sister chromatids separate and reach the opposite poles of the cell

Question 33

what is nondisjunction?

Answer 33

-chromosomes fail to migrate properly in anaphase, so one daughter cell receives extra chromosomes and the other is deficient in this chromosome

Question 34

what is an isochromosome?

Answer 34

-centrome splits transversely
-chromosomes of unequal length

Question 35

what happens during telophase?

Answer 35

-nuclear membrane reforms and nucleolus appears
-Cytoplasm divides and two complete cells are formed
-chromosmes uncoil

Question 36

what is cytokinesis?

Answer 36

cleavage furrow develops around the equator region and daughter cells separate