Forensic biology - control of mitosis

  • Created by: aarafa11
  • Created on: 01-06-20 15:15
How is mitosis characterised
by activation and then deactivation/destruction of proteins
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What initiates specific events in cell division (binary switches)
phosphorylation/dephosphorylation of proteins
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How to involve the formation active of protein complexes
through binding of specific activating proteins to target proteins
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what controls the binding of proteins
+ve and –ve Feedback by a range of proteins
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WHat is the order of the Activation/deactivation of proteins
Drive mitosis in one direction; Ensure processes are competed in the right order; Ensure processes have been completed before the next stage commences
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Why is the order of the Activation/deactivation of proteins important to follow
Cells die without enough nutrients to complete DNA synthesis/mitosis; Chromosome breakage will occur if a cell starts mitosis before S-phase is complete; loss/duplication of chromosomes occur if anaphase begins before sister chromatids are aligned
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What are the check points
1) start/ restriction point 2)G2/mitosis transition 3) metaphase/anaphase transition
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why should you check the start/ restriction point
starting in G1; Once fired, the cell is irrevocably committed to cell division, there is no going back!
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why should you check the G2/mitosis transition
DNA replicated and undamaged? Yes. Proceed to M phase
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why should you check the Metaphase/Anaphase transition
Sister chromatids appropriately aligned on spindle fibres? Yes. Go for separation and cytokinesis
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How many Cyclin dependant kinases (cdks) are involved in the vertebrate cell cycle
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What do Cyclin dependant kinases (cdks) do
Initiate and regulate the events of the cell cycle
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What is the relationship between Cyclin dependant kinases (cdks) and cyclin
Cyclin dependant kinases (cdks) must bind (like enzyme) to cyclin to become active so cdk actively follos the cyclin cycle
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How can you inactivate the Cdk-cyclin complex
Inhibitory proteins
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What are the 4 classes of cyclins
G1-cyclins; G1/S cyclins; S-cylins; M-cyclins
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When does the restriction point happen
late G1
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What does growth factors do to the cell
(cytokines & hormones) push the cell towards division to this point – external stimulus required
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What happens after the restriction point
no external stimulus required – under the control of the cell
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What happens in the DNA is damaged
halt progression from G1 to S phases;
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What proteins are involved in the damage of DNA
Ataxia Telangiectasia & Rad3-related (ATR) & Ataxia-Telangiectasia Mutated (ATM) will sense damage; bockage of DNA replication to later in the S phase;
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What does Ataxia Telangiectasia & Rad3-related (ATR) do specifically
actives Checkpoint Kinase 1 (Chk1)
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What does Ataxia-Telangiectasia Mutated (ATM) do specifically
activates Checkpoint Kinase 2 (Chk2)
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What does Checkpoint Kinase 1 (Chk1) & Checkpoint Kinase 2 (Chk2) do when DNA is damaged
inactivate Cdk complexes, but by different pathways:
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What does Checkpoint Kinase 1 (Chk1) do specifically when DNA is damaged
phosphorylates Cdc25 so that it binds to an adaptor protein that prevents Cdc25 activity
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What does Checkpoint Kinase 2 (Chk2) do specifically when DNA is damaged
works through a Cdk Inhibitor protein (CKI) p21 Result – damaged or incorrectly replicated DNA stops cell division
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WHat regulated the falling levels of G1/S cyclins
mediated by a multi-subunit complex the Skp, Cullin, F-box containing complex (SCF complex)
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What is SCF complexes
Ubiquitin ligase enzymes, catalyses the addition of ubiquitin to target proteins – polyubiquitination; This signals protein for destruction by proteasomes
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what initiates the activation of S-Cdk complex
Rising levels of S-cyclins - cell enters the S phase
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what is necessary for DNA synthesis and why
phosphorylate proteins that initiate the protein to bind to pre-replicative complexes (PRCs)on the DNA
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What does S-Cdk do
inhibits formation of further PRCs - prevents a further DNA replication cycle as cell cycle is in 1 direction; S-Cdk also promote the activation of transcription factors for the genes of proteins required for DNA synthesis
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When does the levels of M-Cycling rise
in G2
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What partially blocks the active site of Cdk-1
T-loop to prevent ATP binding which occur along with the binding of the peptide for catalysis to occur
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what does Cdk-activating kinase (CAK) phosphorylate
an amino acid near the active site – activating the enzyme
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when doesn't Cdk-activating kinase (CAK) phosphorylate
Another protein kinase, Wee 1, has phosphorylated another inhibitory phosphorylation site on M-Cdk complex; end of G2 the cell has accumulated a lot of M-Cdk primed to trigger the start of M phase; inhibitory phosphate placed by Wee 1 is removed
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Activation of M-Cdk
Phosphatase cell division cycle 25 (Cdc25) remove inhibitory phosphate groups from M-Cdk to undo protein kinase; this will activate Cdc25 to control the entry into the M phase
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what regulated cell division cycle 25 (Cdc25)
is ambiguous and is controlled by several phosphorylation sites; Phosphorylation of some sites activates Cdc25, others de-activate it
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What does M-Cdk complex do in G2
stabilises Cdc25 and activates it; Both total and active levels of Cdc25 rise with M-Ckd formation
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Whats the relationship between M-Cdk & Cdc25
Cdc25 activates M-Cdk, which activates Cdc25- a positive feedback loop
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What does active M-Cdk inhibit
the action of Wee 1
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What the purpose of M-Cdk
Spindle assembly; Chromosome condensation; Breakdown of the nuclear envelope; Attachment of sister chromatids to the spindle fibres; Also prevents DNA replication form occurring again in G2
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What regulates the metaphase-anaphase transition
Anaphase-Promoting Complex/Cyclosome (APC/C); it is a Ubiquitin ligase enzyme
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APC/C targets the destruction of 2 major types of protein inmetaphase-anaphase transition
Securin S- and M-cyclins
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An adaptor protein determines the target of APC/C in metaphase-anaphase transition
Securin – adaptor protein is Cdc20; Cyclins – adaptor protein is Cdh1
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What protein bind with what in metaphase-anaphase transition
Cdc20 binds to APC/C first; Followed by Cdh1 late in M phase
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What does securin do in the metaphase-anaphase transition
protects the protein Cohesin that links the sister chromatids together; Without Securin, the enzyme Separase cleaves cohesin – allowing the sister chromatids to separate- Anaphase triggered;
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what is the problem with APC/C-Cdh1 polyubiqinates S- and M-cyclins
marked for destruction
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What does the decrease of cyclins end
kinase activity of their respective Cdks. therefore, The target proteins are dephosphorylated by various phosphatase enzymes; switches flicked off in anaphase
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WHen does the APC/C remains active
until the G1- S transition; Providing a period in which the cell cycle is halted in G1
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why is the spindle important
Operates at the Metaphase-Anaphase transition; Ensures that the sister chromatids of each chromosome are correctly aligned and attached with the spindle fibres
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Spindle Assembly Checkpoint
failure causes increased chance of a daughter cell receiving an abnormal number of chromosomes; Failure to have correct connection of chromatids sends a ‘wait’ signal that stops Anaphase beginning until corrected
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How to change the conformation of Mad2
unattached kinetochores as it acts as enzyme
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What does the new Mad2 do - due to conformation change
negative signal that diffuses away from the unattached kinetochore; The active Mad2, along with other proteins, inhibits Cdc20; thus the destruction of securin through the action of APC/C-Cdc20 cannot occur
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Card 2


What initiates specific events in cell division (binary switches)


phosphorylation/dephosphorylation of proteins

Card 3


How to involve the formation active of protein complexes


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Card 4


what controls the binding of proteins


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Card 5


WHat is the order of the Activation/deactivation of proteins


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