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BoD > Cell cycle > Flashcards

Cell cycle Flashcards

1
Q

Which CDK binds with Cyclin D and in which phase is it expressed?

A

CDK4 and CDK6
G1-phase

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2
Q

Which CDK binds with Cyclin E and in which phase is it expressed?

A

CDK2
G1-phase

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3
Q

Which CDK binds with Cyclin A and in which phase is it expressed??

A

CDK2
S-phase

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4
Q

Which CDK binds with Cyclin B and in which phase is it expressed?

A

CDK1 aka CDC2
G2 and M-phase

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5
Q

Why do cells divide? (what are the cons for being bigger but less rather than smaller but more)

A

> Lower ability to absorb nutrients and remove waste products
Less gas exchange
Cells less likely to respond to extracellular signalling

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6
Q

Describe flow cytometry? (5 marks)

A
  1. Labelled cells suspended in fluid and passed through single file
  2. laser light focussed on cells
  3. Excites any flourescence detected
  4. emitted flourescence detected
  5. Scattered light detected—> measures total cell number.
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7
Q

What is the amount of flouresence directly proportional to in flow cytometry?

A

Amount of DNA
More DNA = more intercalation = more flourescence

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8
Q

What is Flow cytometry used for? (there are 4 uses)

A

Cell counting/sorting
Protein expression
Apoptosis
Cell cycle analysis

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9
Q

What are the 3 common methods to study the cell cycle?

A
  1. Light/time lapse microscopy—> cellsin mitosis are rounded up
  2. DNA binding dyes BrdU, incorporate into new DNA formed in S-phase
  3. Flow cytometry
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10
Q

What is the function of G1?

A

Increase the size of the cell, duplicate organelles, PREPARE FOR DNA SYNTHESIS

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11
Q

What is the function of E2F?

A

TF, stimulates expression of genes needed for the cell cycle

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12
Q

What is Rb?

A

Transcriptional repressor, blocks the function of E2F

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13
Q

What are the 2 ways Rb inhibits E2F and describe each?

A

Passive Repression—> Rb binds E2F and prevents it activating transcription of genes nedded for S-phase
Active repression—> Rb recruits the Sin3 & HDAC proteins, Blocks transcription by modifying chromatin

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14
Q

What is the function of HDAC?

A

HDAC= histone DeAcytylases
Deacetylates histones- closes up chromatin and blocks transcription
Stops polymearse to bind to DNA so no transcription occurs.

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15
Q

Describe the Removal of Active Repression. (4)

A
  1. Cyclin-D-CDK4 or 6 —>phosphorylates Rb
  2. Blocks Sin3 binding to Rb
  3. HDAC—> repression removed=transcription
  4. expression of subset of genes needed for late G1 and early S-phase
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16
Q

Describe the Removal of Passive Repression (3)

A
  1. Cyclin E-CDK2—> 2nd Rb phosphorylation
  2. Blocks Rb binding E2F—> removes passive repression of E2F
  3. Expression of genes needed to complete S-phase:histones, cyclin B, nucleotide synthesis for new DNA
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17
Q

What is the G1 restriction Checkpoint?

A

Point of no return, checks DNA integrity

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18
Q

What has to happen for the cell to go through G1 checkpoint?

A

Cells must inactivate: Rb

Rb —> Transcriptional repressor blocks the function of E2F

E2F —> TF, stimulates expression of genes needed for the cell cycle

19
Q

What cyclins and CDK are in the G1 phase?

A

Cyclin D + CDK4/6
Cyclin E + CDK2

20
Q

What cyclins and CDK are in the S?

A

Cyclin A + CDK2

21
Q

What cyclins and CDK are in the G2 + M?

A

Cyclin B + CDK1

22
Q

What do CKIs do?

A

Inhibit cell cycle progression

23
Q

What is active repression by Sin3-HDAC

A

DNA —> tightly packed around histones

Transcription—> DNA opened up allows polymerase access

Requires histone acetylation

HDACs—> Histone DeAcetylases

De-acetylates histones= closes up chromatin and blocks transcription

24
Q

What is Ori?

A

Region of DNA where replication is initiated
Eukaryotes: have multiple Ori’s
Prokaryotes only 1 Ori cause it has a circular chromosome

25
Q

How is DNA replication controlled?
THERE ARE POINTS FOR EACH STAGE (G1/S)

A

G1: ORC vinds to Ori
After initiation of cell cycle: E2F partially activated->active repression by Rb
Allows expression of E2F target gene CDC6 which binds to ORC
CDC6, ORC & CDT1 recruit inactive 2x MCM helicase
Binding of MCM helicase to DNA forms the pre-replication complex
At G1/S transition: Cyclin C-CDK2 phosph thepre-replication complex
DNA Helicasesunwind DNA—>inactive DNA polymerase recruited
S: Cyclin A-CDK phosphorylates–> DNA polymerase, CDC6, ORC
Polymearse activated, ORC inactivated->dissociates from DNA, CDC6 targeted for destruction->breaks link between Ori and DNA polymerase

26
Q

What drug is used to improve elderly health?

A

Senolytic drugs: kill senescent cells, as SASP is associated with age related disease such as type 2 diabetes, alzheimers etc.

27
Q

What is a kinetochore?

A

Large protein structure built at the centromere allows attachment of the spindle microtubules

28
Q

What is the role of Cyclin B?

A

B controls G2 and mitosis:

CYTOPLASMIC RETENTION SEQUENCE CRS

NUCLEAR LOCALISATION SEQUENCE NLA

CRS is dominant over the NLS
G2 progresses= increased cyclin B

29
Q

How is Cyclin B-CDK1 activated?

A

Inactive: phosphorylated by Wee1, Cyclin B-CDK1 is bound by CRS
CRS phosphorylation by PLK-1 and ERK blocks cytoplasmic retention
Cyclin B-CDK1 enters nucleus remains inactive
PLK-1 phosphorylates and activates CDC25
CDC25 removes CDK1 inhibition
Active cyclin B-CDK1 phosphorylation and furtheractivates CDC25
Positive feedback on cyclin-B-CDK1
Cyclin B-CDK1 can now REGULATE PROGRESSION THROUGH MITOSIS

30
Q

What is Cohesin?

A

Forms a ring like structure around the sister chromatid

31
Q

What is condensin?

A

Restructures and condenses the DNA

32
Q

What does Cyclin B-CDK1 do in late G2 and prophase?

A

Condensin need to be activated
SL1 needs to be inactivated
Cyclin B-CDK1 phosphorylates both. condensin activates, SL1 deactivates
Promotes chromosomal condensation

33
Q

What does Cyclin B-CDK1 phosphorylate in prometaphase?

A

Lamin- causes nuclear membrane to breakdown

34
Q

What is Upiquitin and what are the 3 classes?

A

Protein degradation
3 classes:
E1 activates ubiquitin
E2 receives Ubq from E1 and prepares it for ligations
E3 ligated Ubq to target proteins

35
Q

Cyclin B-CDK1 function in metaphase?

A

Phosphorylates APC and Cdh1 swapped for CDC20
Phosphorylates Seperase and securin binding

36
Q

What happens in anaphase?

A

APC-CDC20 ubiquinates securin releasing seperase
Seperase ubiquitinates cohesin (sister chromatids seperate)
Seperase ubiquitinates Fear and MEN- activates CDC14b

APC-CDC20 ubiquitinates Cyclin-B

37
Q

What happens in Telophase/cytokinesis?

A

CDC14b is the main factor!!
Dephosphorylates Cdh1 and APC –> swap of CDC20 for Cdh1, so APC-Cdh1 and CDC20 alone?!—> Cyclins Ubiquitinated and destroyed
CDC14b Dephosphorylates myosin–> contractile ring seperates 2 daughter cells
CDC14b dephosphorylated Rb->represses E2F
CDC14b dephosphorylates SL1 so transcription restarts
CDC14b dephosphorylates lamin–> nuclear mem reassembly—> CDC14b –> sequestered in newly forming nucleolus

38
Q

What happens in the resriction checkpoint(G1)?
HOW IS THE CELL CYCLE ARRESTED
WHAT HAPPENS WHEN THE DNA IS REPAIRED

A

ATM detects DNA damage causes ATM to become phosphorylated and seperate (they are in pairs).
ATM phosphorylates ChK2–>INDUCE AND STABALISE p53 and inhibit MdM2 is a ubiquitin ligase which targets p53
p53 levels increase—> p21 induced which is a cyclin dependant kinase inhibitor—>Cyclin E-CDK2 inhibited preventing full activation of E2F and preRC
CAUSING THE CELL CYCLE TO ARREST

DNA repaired ChK2 is inactivated so MdM2 is no longer repressed so p53 is ubiquinated–> decrease of p53 and p21 so cyclin E-CDK2 in repressed so entry to S-phase

39
Q

What happens in the G2/M checkpoint?

A

DNA damage activates ATR which phosphorylates ChK1 which inhibit CDC25 and activates Wee1
Wee 1 inhibits Cyclin B-CDK1
CDC25 activates Cyclin B-CDK1
CELL CYCLE ARRESTS
IF mutation on wee1 then cell cycle is unregulated: cancer etc.

40
Q

What happens in the metaphase checkpoint?

A

Negatively regulates APC-CDC20—> Cyclin B-CDK1 phos Cdh1 and APC
APC dissociates from Cdh1 and binds CDC20
APC-CDC20 ubiquitinates securin
MCC bind and inhibit APC-CDC20

MAD proteins sense if spindle fibre is not correctly positioned etc.
When the sister chromatids are correctly loaded onto the mitotic spindle
MAD and BUB will dissociate from APC-CDC20 so they can ubiquinate Securin

41
Q

What is the intrinsic apoptosis pathway?

A

Bcl regulate VDAC and ANT channels
anti apoptotic: Prevent pore opening and cytochrome c leaving the mitochondria
Pro apoptotic: keep pores open and allow cytochrome c to leave the mitochondria
BAX allows cytochrome c to leave throught the VDAC (opening it)
Bcl2 stops VDAC to open for cytochrome c
In high levels BAX can let cytochrome c to leave on it own without VDAC

42
Q

What happens once cytochrome c is in the cytoplasm?

A

Cytochrome c and APAF bind together
This causes a cleavage in Caspase 9 to activate it
This activates a cascade to Caspase 3/or 6
caspase 3 can induce apoptosis or caspase 7 and then apoptosis
Caspase 6 only induces apoptosis

43
Q
A

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