Week 7 Flashcards
(102 cards)
What are the two essential features of cell division?
- faithful replication of genetic material
- accurate segregation into daughter cells
Which phases of the cell cycle make up the interphase?
G1, S and G2 phases
Describe the activity of cyclin and Cdk during the cell cycle.
CYCLIN
- increases linearly from the lowest point during interphase to reach maximum concentration halfway through mitosis
- from there to the end of mitosis: steep fall
CDK
- towards the end of the interphase, cyclin contraction raises from minimum concentration (initiated as the cyclin concentration reaches a threshold)
- beginning of mitosis: steep increase to plateau at maximum concentration
- about 2/3 through mitosis, fall symmetrical to increase
Describe the activation process of Cdk.
Cdk on its own = inactive
binds to cyclin –> still inactive
Wee1 and Cak each phosphorylates a different site of Cdk –> P from Wee1 is inhibitory, P from Cak is activating
inhibitory P removed by cdc25 –> active cyclin-cdk
At what size compared to normal would the cell divide if there was a mutation in the gene coding for cdc25? and in the gene coding for Wee1?
CDC25
divides at a bigger size
WEE1
divides at a smaller size
What does the R point of the cell cycle represent?
at the R point (end of G1): G1/S transition
- production of cyclins E and A
- destruction of nuclear cyclin D1
What are the 6 steps of destruction by a proteasome?
1- recognition of ubiquitine in series by proteasome
2- release of ubiquitine
3- unfolding of protein (energy-dependent)
4- opening of the proteasome to let in the unfolded protein
5- cleavage
6- discharge of amino acids
How many checkpoints are there in each phase of the cell cycle?
G1 - 2
S - 1
G2 - 1
M - 1 (metaphase)
Name 1 proteins, and its substrate, involved in the inhibition of cell division.
Name 3 proteins, and their substrates, involved in keeping the cell from replicating DNA (G0 phase)
p21 –> G1/S-cdk and S-cdk
p16 –> Cdk4 (keeps it from binding to cyclin D)
Rb (retinoblastoma) –> E2F (transcription factor for S-phase genes)
Cdc6 –> origin recognition complex (at origin of replication)
What are the two main mechanisms responding to DNA damage?
activation of p53 –> direct transcription of cdk-inhibitors
activation of CHK2 –> inhibits cdc25 (–> no activation of cdk)
How is the nuclear envelope broken down in mitosis? When does it happen?
phosphorylation of nuclear pore proteins and lamins in prometaphase
To what part of the chromosomes do microtubules from spindles attach? What proteinsare involved?
centromere, through kinetochore and kinetochore microtubules
what is checked at the spindle checkpoint in metaphase?
chromosomes are properly attached and under tension
What disease is caused by defects in cohesion of sister chromatids?
Roberts syndrome
Which enzyme cleaves and dissociates cohesin rings?
separase
What can defects at spindle checkpoint cause?
aneuploidy
What is the cleavage furrow of cytokinesis made of?
contractile ring of actin and myosin
Give 6 signs of a reversible cell injury.
- plasma membrane bleb
- increased intracellular volume
- disaggregated ribosomes
- dilated, vesicular endoplasmic reticulum
- aggregated cytoplasmic elements
- mitochondrial swelling and calcification
Define necrosis. Name 6 different types.
death of tissues following bioenergetic failure and loss of plasma integrity
- coagulative necrosis
- caseous necrosis
- gangrenous necrosis
- colliquative necrosis
- fibrinoid necrosis
- fat necrosis
Name two enzymes that must be inactivated early in apoptosis to allow DNA fragmentation.
- PARP (poly ADP-ribose polymerase)
- ICAD (inhibitor of caspase-activated DNase
How are apoptotic cells recognized? What is the aim?
reorganisation of phosphatidylserine from inner to outer leaflet
if not recognised –> inflammation, risk of necrosis
Name two extrinsic triggers of apoptosis and give their key features.
DEATH RECEPTORS
- receptor interaction
- cytoplasmic signals (death domains…)
- caspase cascade
T/NK CELL MEDIATED
- perforin and granzymes
- cytoplasmic activation
What is the key step involved in apoptosis?
release of cytochrome c from mitochondrion –> allows formation of apoptosomes
What are apoptosomes made of? How do they work?
- adaptor protein
- cytochrome c
- procaspase 9
concentrate activity to push equilibrium towards cell death