Cell growth & cell division (lecture 5)

Question 1

what 3 phases can cells go through?

Answer 1

proliferation
quiescence = pause
apoptosis = death

all tightly controlled

Question 2

what happens in the cell cycle?

Answer 2

cells originate from the division of other cells
cell contents copied and passed onto daughter cells
somatic cell division = mitosis

Question 3

prokaryotic cell cycle

Answer 3

2 phases - replication and division
binary fission

DNA replication thought interphase
cytokinesis

Question 4

eukaryotic cell cycle

Answer 4

4 distinct phases
M phase - mitosis and cytokinesis
S phase - synthesis
G1 and G2

Question 5

what happens in prophase in mitosis?

Answer 5

mitotic spindle forms - made of microtubules
chromosomes condense
nuclear envelope starts to disintegrate

Question 6

what happens in prometaphase in mitosis?

Answer 6

nuclear envelope disintegrated
chromosomes attach to microtubules
chromosomes start to move to centre of cell

Question 7

what happens in metaphase in mitosis?

Answer 7

chromosomes line up on the metaphase plate

spindle attached to centromeres

Question 8

what happens in anaphase in mitosis?

Answer 8

shortening spindle fibres - microtubules contracts

daughter chromosomes pulled to poles

Question 9

what happens in telophase in mitosis?

Answer 9

nuclear envelope reassembles around chromosomes

contractile ring starts to contract

Question 10

what happens in cytokinesis in mitosis?

Answer 10

contractile ring creates cleavage furrow

completed nuclei envelope surrounds decondensed chromosomes

Question 11

what happens in interphase?

Answer 11

cell growth
gene transcription
protein synthesis

G1, S, G2

Question 12

what happens in G1?

Answer 12

first growth phase
recovery from previous division
preparation for DNA synthesis
doubles its organelles

Question 13

what happens in S?

Answer 13

synthesise proteins for DNA replication

replication of DNA

Question 14

what happens in G2?

Answer 14

second growth phase
preparation for mitosis
synthesis of proteins required for division

Question 15

what does the G1 checkpoint check for?

Answer 15

if cell is big enough
environmentally favourable
DNA damage
enough space

Question 16

what does the G2 checkpoint check for?

Answer 16

is DNA replicated
is DNA correct
if cell is big enough
environmentally favourable

Question 17

what does the M checkpoint check for?

Answer 17

all chromosomes attached to spindle

Question 18

what is passage through checkpoints controlled by?

Answer 18

cyclin-dependent kinases (Cdk)

Question 19

what are kinases?

Answer 19

enzymes which add a phosphate group from ATP to an amino acid in a protein

phosphorylation signals that the cell is ready to process to the next stage in the cycle

Question 20

how are Cdk activated?

Answer 20

the binding of cyclins

Question 21

why is there different kinases and cyclins at each checkpoint?

Answer 21

distinct jobs and roles
avoids confusion

cyclins are destroyed as the cycle advances

Question 22

when does the cell commit to DNA synthesis?

Answer 22

during G1

Question 23

what is G0 phase?

Answer 23

quiescent resting state
no growth, only maintain ace
can reenter G1

can last days, weeks or years - reversible G0 cells
can be indefinite - irreversible G0 phase

Question 24

what are growth factors?

Answer 24

stimulate cell growth, division and differentiation
continuation of cells through G1 requires specific GFs

only low cons required
cells deprived of growth factors enter G0
growth factors found in blood

Question 25

what is apoptosis?

Answer 25

programmed cell death
physiological way for a cell to die
a regulated process

Question 26

why does apoptosis occur in cells?

Answer 26

damaged/infected DNA
didn’t pass checkpoints
failed protein folding
bodyplans

Question 27

what are the characteristic series of changes in apoptosis?

Answer 27

cell shrinks

nuclear condensation and fragmentation

blabbing triggers phagocytosis

apoptotic bodies will be digested and recycled

Question 28

what is necrosis?

Answer 28

accidental cell death due to injury (physical/chemical)

nuclear swelling 
membrane becomes leaky 
cell bursts - lysis 
cell contents released into tissues 
triggers inflammatory response 

messy process

Question 29

when is apoptosis triggered?

Answer 29

PHYSIOLOGICAL ACTIVATION
crucial for embryonic development
maintaining homeostasis

PATHOGENIC ACTIVATION
viral infections trigger apoptosis
heatshock, toxins
removal of stressed or damaged cells

Question 30

what activates apoptosis?

Answer 30

hormonal signals

direct signal from contacting cell

Question 31

what suppresses apoptosis?

Answer 31

survival factors

contact with extracellular matrix

Question 32

what is the sequence leading to apoptosis?

Answer 32

1) DNA damage activates p53 (guardian of the genome)
2) activated p53 blocks progression at G1 checkpoint
3) mitochondrial membrane rupture - leak cytochrome c
4) cytochrome c in cytosol activates caspases to cause a cascade of events
5) caspase cascade leads to activation of Dnase and cleavage of lamins and cytoskeleton
6) apoptosis

Question 33

what do activates caspases do?

Answer 33

cleave nuclear lamins
• leads to nuclear fragmentation

activate Dnase
• cuts cells DNA into fragments

cleave cytoskeleton
• cell detaches from neighbours
• cell looses contact with extracellular matrix
• cells round up