cell cycle

Question 1

what 5 things affect rate of cell division

Answer 1

embryonic vs adult, complexity of system, necessity for renewal, state of differentiation (antagonistic with division), tumour (lose ability to control, and don’t follow rules)

Question 2

define cell cycle

Answer 2

orderly sequence of events in which a cell duplicates its contents, segregates them and divides in two

Question 3

2 overall phases of regulated progression through cell cycle

Answer 3

M-phase (mitosis), interphase

Question 4

what happens during mitosis

Answer 4

nuclear division, cell division (cytokinesis)

Question 5

what happens during interpahse

Answer 5

DNA and organelle duplication, increase in protein synthesis

Question 6

what is the most vulnerable period of the cell cycle

Answer 6

mitosis

Question 7

why is mitosis the most vulnerable period of the cell cycle

Answer 7

cells are more easily killed (irradiation, heat shock, chemicals), DNA damage can’t be repaired, gene transcription is silenced

Question 8

4 phases within interphase

Answer 8

G0, G1, S, G2

Question 9

what happens in G0

Answer 9

cell cycle machinery dismantled; cell does its function (e.g. secretion)

Question 10

what happens in G1 phase (Gap)

Answer 10

decision point after mitosis/G0

Question 11

what happens in S phase

Answer 11

synthesis of DNA and protein

Question 12

what happens in G2 phase (Gap)

Answer 12

decision point before mitosis

Question 13

what 3 things are increased in S phase

Answer 13

initiation of translation, elongation and capacity for protein synthesis

Question 14

how is mitochondrial replication in S phase different to replication of other organelles

Answer 14

must coordinate with replication of mitochondrial DNA

Question 15

what does the centrosome consist of

Answer 15

2 centrioles at 90 degrees to each other, maintained in position by interconnecting fibres

Question 16

what are centrioles

Answer 16

barrels of 9 triplet microtubules

Question 17

2 functions of centrosome

Answer 17

microtubule organising centre (MTOC) and mitotic spindle

Question 18

life cycle of centrosomes during mitosis

Answer 18

during G1, microtubules grow from centrosome (pair of centrioles), before one centriole detaches -> during S, they duplicate -> in M, when cell divides, each cell has a fully functioning centrosome, consisting of 2 centrioles and microtubules

Question 19

what do microtubules polymerise from in centrosomes

Answer 19

nucleating sites (y-tubulin ring complexes), which encompass a pair of centrioles

Question 20

6 phases of mitosis

Answer 20

prophase -> prometaphase -> metaphase -> anaphase -> telophase -> cytokinesis

Question 21

what happens in prophase

Answer 21

condensation of chromatin

Question 22

stages of chromatin condensation in prophase

Answer 22

chromatin -> condensed scaffold-associated form -> extended scaffold-associated form -> 30nm chromatin fiber of packed nucleosomes -> “beads on a string” form of chromatin around histone proteins -> short region of DNA double-helix

Question 23

in prophase, what does each condensed chromosome consist of

Answer 23

2 sister chromatids, which are joined at the centromere which is associated with a kinetochore

Question 24

3 things that happen between prophase and late prophase-prometaphase

Answer 24

replicated chromosomes condense -> duplicated centrosomes migrate to opposite sides of nucleus and organise assembly of spindle microtubules -> mitotic spindle forms outside nucleus between 2 centrosomes

Question 25

3 stages of spindle formation

Answer 25

radial microtubule arrays (ASTERS) form around each centrosome MTOC -> radial arrays meet -> polar microtubules form (dynamic in this position at centre of cell)

Question 26

what happens in metaphase

Answer 26

chromosomes align at equator of spindle

Question 27

2 stages of prometaphase

Answer 27

early, late

Question 28

3 things that happen in early prometaphase

Answer 28

breakdown of nuclear membrane -> spindle formation largely complete -> attachment of chromosomes to spindle via kinetochores (at centromere)

Question 29

3 things that happen in late prometaphase

Answer 29

microtubule from opposite pole captured by sister kinetochore -> chromosomes attached to each pole progress to middle -> chromosome slides rapidly towards centre along microtubules (CENP-E senses kinetochore tension to ensure this is correct)

Question 30

what happens in anaphase

Answer 30

paired chromatids separate to form daughter chromosomes

Question 31

within the multiprotein complex, what protein holds sister chromatids together, and hence must be broken down

Answer 31

cohesin

Question 32

2 stages of anaphase

Answer 32

A, B

Question 33

what 3 things happen in anaphase A

Answer 33

breakdown of cohesin -> microtubules get shorter -> daughter chromosomes pulled toward opposite spindle poles

Question 34

what 2 things happen in anaphase B

Answer 34

daughter chromosomes migrate towards poles -> spindle poles (centrosomes) migrate apart

Question 35

what 3 things happen in telophase

Answer 35

daughter chromosomes arrive at spindle -> nuclear envelope reassembles at each pole -> assembly of contratile ring (of actin and myosin filaments, creating cleavage furrow)

Question 36

what 6 things happen in cytokinesis

Answer 36

new membrane inserted -> acto-myosin ring contracts -> midbody begins to form -> interphase microtubule array reassembles -> chromatin decondenses and nuclear substructures reform -> midbody splits

Question 37

what 2 things happen if something goes wrong during cell cycle (cell not big enough or DNA damage)

Answer 37

cell cycle arrest, programmed cell death (apoptosis)

Question 38

where does cell cycle arrest occur

Answer 38

at checkpoints (G1 and spindle check point); can be temporary (i.e. following DNA repair)

Question 39

3 occasions when apoptosis occurs and cell cycle progression aborted and cell destroyed

Answer 39

if DNA damage is too great and can't be repaired, chromosomal abnormalities, or with toxic agents