(L2) Growth: Cell division and cell cycle

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Failure to regulate growth leads to what?
Cancer
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What stages does interphase include?
G1 phase, S phase and G2 phase
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What stages does M phase include?
Mitosis and cytokinesis
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How long does a complete cell cycle take in a mammalian cell?
24 hours
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How long does DNA synthesis take?
12 hours
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How long does M phase last?
1 hour
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What other state can a cell go into so it isn't undergoing the cell cycle continuously?
G0 phase which is the resting phase
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Name the 2 types of yeast cell cycle?
Fission and budding
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Name a model budding yeast organism
Saccharomyces cerecisea
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Name a model fission yeast organism
Schizosaccharomyces pombe
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What kingdom does yeast come from?
Fungi
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Name some advantages of using yeasts as model organisms
Small genomes, easy to make and select mutants, easy to clone genes and test their function, rapid growth (cell cycle- 2hrs)
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What does CDC stand for?
Cell division cycle
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What are CDC mutants?
Mutant cells that have abnormal cell cycles
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What can blockage in the cell mean?
It can be lethal and cause cell death or cancer
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What can happen to the mutants if there is a change in temperature?
The mutants can be temperature sensitive, so an increase in temperature can activate the CDC mutation
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How is the cell cycle controlled?
Via certain checkpoints
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What are the checkpoints to ensure?
Conditions are appropriate for the next stage and each stage of the cell cycle is completed
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What is a key check?
That DNA replication is completed fully
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What other checks are there?
Is the environment favourable? Is the cell big enough? Is DNA synthesis complete? Is the DNA damaged?
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Name 3 major checkpoints
1. Commitment to DNA synthesis (in G1): start (yeast) restriction point (mammals), 2. Commitment to enter mitosis (G2), 3. Commitment to complete mitosis (in M)
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What processes does control rely on?
Protein phosphorylation and dephosphorylation
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What are the principle enzymes that control the cell cycle?
Cyclin-dependent protein kinases (Cdks)
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When are Cdks active?
Only in the presence of proteins called cyclins
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What happens to the level of cyclins during the cell cycle?
They rise and fall throughout the cycle
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What is a cyclin-Cdk complex and what do they do?
They are the complex formed when a cyclin binds to a Cdk and they trigger the next stage of the cell cycle
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Describe the cyclin and Cdk content in yeast
Yeast only have one Cdk but they have several cyclins
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Describe the cyclin and Cdk content in vertebrates
They have 4 Cdks as well as several cyclins
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How many different classes of cyclin are there?
4 different classes universal in different organisms
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Which class is in most cells?
In late G1 phase, G1-cylins control initiation of processes leading eventually to cell division
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What are the universal classes of cyclins?
G1/S-cylins (initiate S phase), S-cyclins (initiate DNA synthesis), M-cyclins (Initiate mitosis)
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What exactly do cyclins direct Cdks to do?
Phosphorylate specific target proteins
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When M-Cdk phosphorylates its target proteins, what does this cause?
(Initiation of mitosis ) Breakdown of the nuclear envelope, chromosome condensation, assembly of mitotic spindles and attachment of chromosomes, cytoskeleton and organelle rearrangement
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Give some examples of specific targets
Lamin protein of nuclear lamella, proteins in condensin complex required for chromosome condensation
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What controls cyclin concentrations?
Cyclin synthesis (cyclins accumulate during the cell cycle), cyclin degradation by proteolysis
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What are protein concentrations determined by?
The balance of the synthesis and degradation reactions
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`Name a major mechanism in protein turnover
Proteasomes
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What is a proteasome?
A large complex, nearly 1% of cellular protein, ATP-dependent, two main parts: 1) hollow cylinder where proteolysis takes place, each ring contains 7 polypeptides, 2) Cap that binds and unfolds proteins to be destroyed (associated w/ ATP-hydrolysis)
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What small protein needs to be attached to a protein in order for it to be degraded
Ubiquitin (76 amino acids)
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What adds the ubiquitin to the protein that is going to be degraded?
Ubiquitin ligases
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How does ubiquitin bind to the protein?
The carboxy-terminal glycine of ubiquitin is attached to the amino group of a lysine side chain on the target protein
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What bond does ubiquitin bind with?
Peptide
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What causes the ubiquitin ligases to attach the ubiquitin?
Degradation signals
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Give 2 examples of degradation signals
1) Non-specific (Proteins have abnormal structures), 2) Specific (Proteins with short lives)
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How many ubiquitin ligases do cells have?
Multiple, different ligases recognise different signals
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Other cards in this set

Card 2

Front

What stages does interphase include?

Back

G1 phase, S phase and G2 phase

Card 3

Front

What stages does M phase include?

Back

Preview of the front of card 3

Card 4

Front

How long does a complete cell cycle take in a mammalian cell?

Back

Preview of the front of card 4

Card 5

Front

How long does DNA synthesis take?

Back

Preview of the front of card 5
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