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Cell Division and Death Flashcards

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1
Q

Examples of extracellular stimuli that cells are bombarded with

A

signaling molecules (growth factors)
physical environment (O2 levels, nutrient availability)

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2
Q

What do cells do when exposed to extracellular stimuli

A

integrate information and decide how to react

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3
Q

WHat changes occur in a cell in response to extracellular stimuli

A

changes in proliferation, cel death and differentiation

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4
Q

what determines a cells response to the same extracelular stimuli

A

the intrinsic properties of the cell

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5
Q

Why might the same stimuli cause different effects in different cells

A

different cell types or the same type in a developing adult respond differently due to their intrinsic properties (internal characteristics)

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6
Q

what is cell proliferation

A

Interphase (G1, S and G2 phase)
follows by M phase Mitosis

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7
Q

What are the three steps in cell proliferation

A

DNA replication (duplication genetic material)
DNA segregation (splitting into each cell)
Cytokinesis (division to form two new cells)

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8
Q

What initiates cell proliferation

A

extrinsic or intrinsic to cell

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9
Q

WHat is cell proliferation essential for

A

reproduction
embryogenesis and tissue growth
tissue regeneration and repair

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10
Q

do different cells have different rates of cell division

A

Some divide rapidly (embryonic) and others do not divide (neurons)

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11
Q

Where does regulation occur

A

in cell cycle

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12
Q

what rate does the cell cycle have

A

embryonic = 30 mins
adult human = 24hrs

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13
Q

stages in cell division

A

G1
S (DNA synthesis)
G2
M (Mitosis)

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14
Q

What occurs in Mitosis and when does it happen in the cell cycle

A

last stage
division of nucleus and cytokinesis

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15
Q

What happens in G1 phase

A

Increase size
single copy of chromosomes
dispensable very rapidly dividing cells
vary weeks to years

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16
Q

what happens in s phase

A

dna replication
2 sister chromatids formed from each chromosome

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17
Q

What hppens to cells that do not divide during G1

A

enter G0

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18
Q

WHat happens in G2 phase

A

preparation for mitosis
assembles structures that move chromatids to opposite sides of dividing cell

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19
Q

What happens in G0 phase

A

resting phase of cell
some return to G1 (response to extracellular signals)
some differentiated cells never undergo division (neurons)

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20
Q

Where do cells mostly spend their time and for how long

A

G1 = 11hrs
S = 8
G2 = 4
M = 1

23 hours

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21
Q

what is progress through the cell cycle dependent on

A

cyclin-dependent kinases (CDKs)

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22
Q

what are kinases

A

proteins that phosphorylate to other proteins

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23
Q

when are CDK’s active

A

bound to cyclins

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24
Q

what happens when CDK binds to cyclins

A

alters CDK shape exposing active site

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25
What happens during phosphorylation by CDKs
peach CDK has specific target actives or inactivates target proteins regulation of cycle
26
step by step of CDK process
1) Cyclin binding changes CDK exposing active site 2) Protein substrate and ATP bind to CDK 3) Protein substrate is phosphorylated 4) Phosphorylated protein regulates the cell cycle 5) Each CDK has specific protein targets
27
are all CDK complexes the same
different CDKs and cyclins interact to form different disparate complexes e.g. cyclin B/CDK1 regulates M phase
28
what are cyclins
group of proteins whose role is to bind to CDK's to activate the CDK
29
what is RB full name
Retinoblastoma
30
What does an activated RB protein do
in rare form of eye cancer inhibits progression through cell cycle RB is a restriction point that prevents progression from G1 to S phase
31
what is RB regulated by
CDK/cyclin complex
32
How is RB controlled
CDK/cyclin complex phosphorylates RB protein to inactivate it RB no longer prevents cell cycle Cell can enter S phase
33
how do cyclins regulate the cell cycle
cyclins synthesised and destroyed at different points concentrations are different at different times present of absence regulates activity of CDKs
34
Summarise how the cell cycle is regulated
CDKs regulate cell cycle CDK's are regulated by cyclins CDK's activated by cyclin binding CDK's phosphorylate target proteins enabling cell cycle progression Cyclin after breaks down and returns CDK to inactive state
35
what are the checkpoint triggers for each cell cycle phase
G1 = DNA damage (unfavourable conditions) S = Incomplete replication (dna damage) G2 = Unduplicated centrosomes (DNA dam) M = chromosome unattached to spindle
36
What happens during these checkpoint triggers
detect problem pause to repair if cant repair death pathways activated
37
Process that occurs during DNA damage of G1if DNA is repaired
1) DNA damaged during G1 2) p21 produced 3) p21 binds to CDK2 4) cyclin binding prevented 5) CDK2 inactive 6) Cell cycle paused 7) if DNA repaired p21 breaks down 8) Cyclin binds to CDK2 9) cell cycle resumed
38
What happens if DNA cannot be repaired in G1 phase
apoptosis
39
What forms tumours
oncogenes
40
How do oncogenes work
positive regulators of cell division are overactive/ highly expressed leads to unregulated cell division
41
how do tumour suppressors work
negative regulators of cell division makes cancer cells inactive RB protein blocks cell cycle continue
42
how is cancer treated
Agents that target cell cycle act at diff stages to stop cell division also affect non cancerous tissues (hair follicles, intestinal cells)
43
5 stages of mitosis
poophase prometaphase metaphase anaphase telophase (follows by cytokinesis)
44
stages of how dna is packaged
1) Nucleosome 2) Chromatin 3) Scaffold-associated chromatin 4) Condensed chromatin 5) Compacted chromosome
45
What happens during nucleosome first stage
dna wraps around histones forming nucleosomes
46
what happens during chromatin
nucleosomes pack into coils forming chromatin fibres
47
What happens during scaffold associated chromatin
chromatin fibres fold to form loops attached to a protein scaffold
48
What happens during condensed chromatin
loops condense in interphase nucleus forming condensed chromatin
49
what happens during compacted chroosome
during mitosis loops coil further forming a condensed chromosome
50
process of how dna is packaged full thing
1) DNa wrapes around histones forming nucleosomes 2) Nucleosomes pack into coil forming chromatin fibres 3) Chromatin fibres fold to form loops attached to a protein scaffold 4) Loops condense in interphase nucleus forming condense chromatin 5) During mitosis loops coil further forming a condensed chromosome
51
What happens during prophase
-chromatin condenses -> chromosomes -identical sister chromatids -centrosomes move to opposite poles of cell -spindles
52
what happens in prometaphase
-nuclear envelope breaks down -spindles finish forming and attach to chromosomes
53
what happens during metaphase
-centromeres line down equator of cell -chromosomes align at metaphase plate -cell cycle checkpoint activated at end if chromosome attached
54
What happens during anaphase | whats regulated, activated and separated
-chromatids separate -regulated by m phase cyclin-CDK -activates anaphase-promoting complex (APC) regulated by checkpoint
55
WHat are the two groups of fibres in the spindle
polar microtubules kinetochore microtubules
56
What are polar microtubules
run from one pole to other connect centrosomes; stabilise structure
57
what is a kinetochore
protein complex that forms in centromere attach sister chromatids to centrosomes on opposite sides of cell
58
what are kinetochore microtubules
attach kinetochores to spindle
59
what happens during telophase
-spindle dissapears -nuclear envelope forms around daughter chromosome -chromatin decondenses
60
What is cytokinesis driven by
actin myosin contraction forming a contractile ring
61
what happeens in ccytokinesis | what structure is formed
cytoplasm divides following nuclear division actin myosin contracts forming contractile ring resulting in two daughter cells
62
are the daughter cells identical
should be but concentration of organelles and signalling factors etc may vary fate of daughtere cells may differ
63
what are the types of cell death
Necrosis Apoptosis Autophagic cell death necroptosis
64
What is necrosis
death by damaged cell cell damaging agents toxins, O2, nutrient starvation no energy required
65
what happens during necrosis step by step
1) cell swelling, loss of membrane integrity, cell lysis 2) release contents 3) attracting leucocytes and phagocytes to remove debris 4) can damage surrounding tissue
66
What is apoptosis
regulated form of cell death programmed self destruction active proceess (energy needed)
67
what happens during apoptosis step by step
1) Cell detached from neighbours 2) shrinks 3) chromatin condenses and digested into apoptotic bodies (fragments) 4) Apoptotic bodies engulfed by neighbouring atoms -> components reused 5) cell contents not released no inflammatory response
68
Why does apoptosis occur in cells
if cell is no longer needed control cell number undergone pathogenic changes = dna damage, virus infected, immune cells (restore homeostasis after infection or remove cells that recognise autoantigens)
69
What is apoptosis regulated by
intrinsic signals e.g. hormones, growth factors, toxins, viral infection, extensive DNA damage
70
What do these intrinsic signals do
activate receptors activate signalling pathways that trigger apoptosis
71
what may be targeted by intrinsic signals
mitochondria ceell death due to failed cellular respiration
72
namee of enzymes using during apoptosis activation
caspases
73
what cell death genes are found to affect apoptosis
Ced-3 = caspase (causes apoptosis) Ced-9 = Bcl-2 (prevents apoptosis)
74
What do proteases do
cleave peptide bonds between amino acids cleave specific targets after an aspartic acid residue present in cytoplasm and mitochondria
75
what are caspases inhibited by
IAP proteins (inhibitors of Apoptosis)
76
How are caspases activated
Cleaved mediated by initiator caspases
77
what are executor caspases activated by
cleavage by initiator caspases
78
what do executor caspases do
hydrolyse proteins of nuclear envelope, nucleosomes, cytoskeleton, cell membrane leading to cell death
79
extrinsic pathway process
1) Extrinsic signal binnds to death receptor on cell surface 2) procaspase -8 or -10 activated 3) initiator caspases form 4) initiator caspases activate executor procaspases -3, -6 -7 5) Active executor induces apoptosis | Triggered by external signals
80
Intrinsic pathway process
1) Mitochondria release cytochrome C into cytoplasm 2) Cytochrome C binds to Apaf-1 3) Complex activates procaspase -9 4) Caspase-9 activates executor procaspases 5) Executor caspases trigger apoptosis
81
What can trigger caspase activation
Increasing mitochondria
82
What does Bcl-2 control in a cell
mitochondria permeability
83
What does Bcl-2 do for apoptosis
inhibits it Prevents opening of membrane pores preventing apoptosis
84
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