Mitosis and cell cycle control W5 Flashcards
Varying lengths of cell cycles
Embryonic cells may take two hours
Cells in an adult may take 20 to 24 hours
Stages of the cell cycle
Interphase:
1. G1 growth
2. S growth and DNA rep
3. G2 growth and final preparations for division
Mitosis
1. Prophase.
2. Prometaphase.
3. Metaphase.
3. Anaphase.
5. TelephaS
Stages of the cell cycle
Interphase:
1. G1 growth
2. S growth and DNA rep
3. G2 growth and final preparations for division
Mitosis
1. Prophase.
2. Prometaphase.
3. Metaphase.
3. Anaphase.
5. Telephase
6. Cytokinesis.
How long is interphase?
20 to 22 hours
How long is the mitotic phase?
Typically one to 2 hours
Interphase G1
Cells a metabolically active
Cells increase in size
Cell doubles its organelles, i.e. ribosome and mitochondria which makes lots of proteins and ATP
Cells accumulate pre-curses that will be used for DNA synthesis
Chromosomes in nucleus or deacon Dund
S stage
DNA replicate and each chromosome is duplicated
Each copy of a duplicated chromosome is called a crew and will remain attached by the century until the end of mitosis
Protein complexes called kinetochores develop on either side of the century during cell division
Interphase G2
Cells increase in size again
Cell synthesise proteins that will assist cell division: like tubulin
Centre is duplicated and both copies remain together on one side of the nucleus
Mitosis requires what?
Microtubules
The myotic spindle is made of microtubules and segregate daughter chromosomes to opposite poles of the cell
The centre is the principal micro tubular organising centre
The Centre must be duplicated before M phase begins
Three classes of Spindel microtubule
- Astral
- radiating from the centrosome and thought to contribute to pole separation
- cling to cell memb
- star shaped - Kinetochore
- microtubules - attach to kinetochore on the
duplicated chromosome - Overlap microtubules
- (interpolar) - overlap at the equator, responsible for bipolar shape of the spindle
Microtubule motor proteins
- Kinesins : walk towards the positive end of a microtubule
- Dyneins : move towards the microtubules negative end.
Mitotic machinery
• Prior to entering the first stage of mitosis (prophase) the microtubules
are in dynamic state
• Microtubules switch between periods of growth to shrinkage
(catastrophe) and shrinkage to growth (rescue)
• Phosphorylation of microtubule-associated protein (MAP) &
catastrophins alter stability of microtubules (at the + end) & governs
assembly of the mitotic spindle
Five stages of mitosis
- Prophase.
- Prometaphase
- Metaphase.
- Anaphase.
- Telophase
- Cytokinesis.
- Prophase.
Replicated, chromosomes condense
Mitotic spit a sample between the two centres which began to move apart
- Prometaphase
Breakdown of nuclear envelope
Disassembly of intermediate filaments supporting the nuclear envelope
Randomly probing MT encountering a chromosome will buy into it and will eventually attach to the kinetochore
Chromosome migrate within cell
- Metaphase.
Kinetochore MTs attach sister chromatids to opposite poles of the spindle
Chromosomes a line along equator of a spindle
- Anaphase.
Sister cremated separate synchronously: two daughter chromosomes pulled toward the spindle pole it faces
Kinetochore MTs shorted by the polymerisation: chromosomes are pulled pole ward
Interpolar MTs grow and push spindle poles further apart
Astral MTs pull the spindle pole versus the cell periphery, attaching to the cell cortex
- Telophase
Daughter chromosomes arrive at opposite poles and deacondense
Nuclear envelope forms around the daughter chromosome
The division of cytoplasm begins with the formation of the contractile ring
- Cytokinesis.
Myosin accumulates and begins to form contractile ring with actin
The cytoplasm is divided by contractile ring
Each daughter cell will receive its complement of organelles (mitochondria, ER, ribosome)
The contractile ring
It is the cytoskeletal structure responsible for cytokinesis
Consists mainly of actin and myosin filaments
It is arranged in a ring around the equator of the cell
It starts to assemble beneath the plasma membrane at the end of mitosis
As the ring contracts, it pulls the membrane inwards, dividing the cell into
It disassembles completely once the cell is divided in to
How do cells controlled their proliferation?
The progress of the cell cycle needs to be carefully controlled: in sequence, in timing, in response to external signals
They control this by controlling the activity of their proteins
How to sell control the activity of their proteins
- Phosphorylation/dephosphorylation
- Make more/inhibit and degrade.
- Phosphorylation/dephosphorylation
Proteins can be switched on and off
1 - by phosphorylation: the transfer of a phosphate group from ATP to the OH group on a protein. This is done by a protein kinase
2 -by dephosphorylation: removal of the phosphate group. This is done by a phosphate
- Make more/inhibit and degrade.
Proteins can be switched on: De novo synthesis from mRNA
Proteins can be switched off: binding to an inhibitory protein that keeps it inactive, by targeting for degradation
True or false? Both phosphorylation and dephosphorylation can activate or deactivate the protein depending on where the phosphate is added or removed?
T
True or false? Inhibitory proteins inhibit the function/activity of other proteins that they bind to?
T
Q. Protein activity can be altered by:
a) Making new protein
b) Targeting protein for degradation
c) Binding to inhibitory proteins
d) All of the above
D
Cyclins
Have no enzymatic activity
Can be A, B, C, D one, D2, D3, E
Their concentrations vary in a cyclical fashion during the cell cycle because they undergo synthesis and degradation through each cell cycle
When cyclins bind to CDKs they can become enzymatically active
Different cyclins are expressed in different phases of the cell cycle and combine with different CDKs :
D - G1 phase
E - G1 to S phase
A – G2 phase
B – mitose
What needs to happen for a cyclin-CDK to be maximally active
The CDK has to be phosphorated at three sites and dephosporylated at two sites
True or false? Cyclins have enzymatic activity?
F
True or false? Cyclin dependent kinases are constitutively active throughout all stages of cell cycle?
F
What is S phase controlled by?
S-CDK complexes
What is M phase controlled by?
M-CDK complexes and Anaphase promoting complex APC
What is continue proliferation G1 to S controlled by?
G1-CDK complexes and Rb
What is DNA damage checkpoint G1 to S controlled by?
P 53
- Replication of DNA.
DNA replication must occur first and only once per cycle
It begins at origin of replication when the pre-replicative complex is assembled
S-CKD in replication of DNA
- Triggers DNA replication recruiting DNA polymerase.
- Blocks re-replication by causing dissociation and degradation of CDC6 and exports other proteins from the pre-replicative complex from the nucleus.
True or false? DNA replication can only occur if S-CDK complex is active
T
Which of the following is INCORRECT about the M-CDK complex?
A) It triggers rearrangement of microtubules
B) It triggers DNA to condense into chromosomes
C) It triggers nuclear envelope breakdown
D) It is composed of cyclin B and APC
D
True or false? Securin needs to be phosphorylated by APC in order for chromosome segregation
F
True or false? APC targets the inhibitory protein securin for degradation allowing the enzyme separase to become active
T
True or false? APC adds ubiquitin groups to cyclin B at the end of Mitosis
T
True or false? Rb is activated by phosphorylation causing it to activate gene
transcription
F
True or false? Growth factor signals allow activation of G1-CDK
T
True or false? G1-CDK binds to DNA to cause transcription of S phase cyclins
F
True or false? Without DNA damage p53 is degraded
T
True or false? MDM2 is a protein kinase
F
Which of the following is incorrect about
p53?
A) It promotes the transcription of DNA repair genes
B) It promotes cell death if there is too much DNA damage
C) It inhibits the production of CKI
D) It is known as the guardian of the genome
C
