Cell replication Flashcards
Describe how cells divide at different rates and give examples
1) terminally differentiated cells (eg neurons, cardiomyoctes) never divide
2) adult human cells could well take 24 hours to divide, but early frog embryo cells take about 30 minutes
3) intestinal epithelial cells take around 20 hours to divide, whereas hepatocytes take around 1 year
What cells never divide
neurons and cardiomyocytes
Describe and draw the cell cycle and label the parts of it
G1, S and G2 = interphase G= gap S = synthesis M is the division also G0 phase Can only go one way around cell cycle (can't reverse )
Why is the decision of a cell to divide or not to divide an important decision
cell division takes a lot of energy (is busy)
doubles in size, tears itself apart, and 3 million bp replicated
Describe a cell in G0
‘quiescent cells’
- without any relevant stimulus cells stay in G0
- they are still ‘busy’ (not dormant)
- differentiated cells that are to perform specific functions are not in the cycle (but they are not dormant)
What do you need for a cell to exit G0
a signal
Why are checkpoints necessary in the cell cycle
- to check if the cell is in a fit state to cycle
- to monitor the external environment ( eg growth factors and nutrients)
- might pause bc it found a problem in the DNA replication and then undergo apoptosis
Where are 3 checkpoints and what do they check for
1)checkpoint in mitosis
‘are chromosomes properly attached to the mitotic spindle’
2) checkpoint before entering S phase
‘is the external environment alright’
3) G2 checkpoint
‘are there any mistakes in DNA replication’
‘is all DNA replicated’
Describe the signalling cascade
1) tyrosine kinase/ growth factor receptors will pick up growth factors that signal that the environment is fine and so is fine to divide
2) the pathway serves to amplify that signal
3) MAP kinases (eg RAS/Raf/Mek/ERK) are involved
Give some MAP kinases and tell me the significance of them when it comes to the cell cycle
Ras, Raf, Mek, ERK
have the potential to become oncogenes and drive erroneous cell cycle
What turns on C-Myc production
a growth factor
What type of a gene is C Myc and when is it overexpressed
oncogene
over expressed in some tumour
What does C myc promote
G0 to G1 progression
Describe some characteristics of cyclin dependent kinases (CDK)
- are present in all PROLIFERATING CELLS
- are not turned on until they combine with a cyclin
- can be phosphorylated and dephosphorylated at serine/threonine/tyrosine residues
- key signalling role
describe how cyclin levels vary in the cell
-v low at the end of mitosis and increase in a curved way until mitosis ends
