Cell Replication Flashcards
what is the cell cycle?
orderly sequence of events in which a cel duplicates its contents and divides in 2
give a brief overview of the stages of the cell cycle
- cell growth and chromosome replication
- chromosome separation
- cell division (cytokinesis)
what factors affect the rate of cell division?
age, complexity of system, need for renewal, state of differentiation, tumour cellss
which cells never divide?
neuron and cardiac myocytes
which stages make up interphase?
G1, S, G2
what happens in S phase?
DNA replication
what happens in M phase?
mitosis (nuclear division)
cytokinesis (cytoplasmic division)
what is G0?
quiescent phase
in the absence of a stimulus, cells go into G0
give example of cells which stay in G0 for long periods
neurons, skeletal muscle, hepatocytes
what do checkpoints in G1 do?
check if environment’s favourable to enter S phase
what do checkpoints in G2 do?
check all DNA is replicated
check all damaged dna is repaired
what do checkpoints in mitosis do?
check all chromosomes are properly attached to the mitotic spindle
what does c-Myc do?
a transcription factor which stimulates the expression of cell cycle genes and promotes G0 to G1 transition
its an oncogene that’s over expressed in many tumours
when is c-Myc produced?
in response to the detection of a growth factor
How do we get cell growth? (Leaving G0 to G1)
Growth factors bind to tyrosine kinase receptors, which triggers an intracellular signalling pathway which ultimately leads to protein synthesis increasing and protein degradation decreasing, stimulating cell growth
what two things can occur if something goes wrong with cel replication?
- Cell cycle arrest - can be temporary while damage is being fixed
- Programmed cell death = apoptosis
What happens to the cell when the DNA damage is too great and cannot be repaired?
Programmed cell death = apoptosis
In the absence of a stimuli to progress into the next stage of replication, what happens to the cell?
Cells go into G0 phase (quiscent phase)
What does the exit from G0 phase require?
Growth factors and intracellular signalling cascades
What forms when cyclins bind to cyclin dependant kinases?
They form an activated cyclin-CDK complex
does the concentration of cyclins in the cell fluctuate?
yes
when is the Cdk active?
only during mitsois
as soon as cyclin has basically disappeared, no activity of cyclin dependant kinase
b
cell detects growth factor
production of c-Myc
target gene for c-Myc = cyclin D (first cyclin needed to get into S phase)
what do protein kinases cascades lead to?
signal amplification- kinases activate many others, have targets, can phosphorylate lots of things
regulation: dephosphorylate to stop the cycle
intracellular signalling cascade
kinase phosphorylates
what is cell cycle control based on?
cyclically activated and expressed proteins
where are cyclin-dependent kinases present?
in proliferating cells throughout the cell cycle
what is the activity of cyclin-dependent kinases regulated by?
interaction with cyclins
phosphorylation
when are cyclins expressed, regulated and synthesised?
transiently expressed at specific points in the cell cycle
regulated at level of expression
synthesised then degraded
