Cell cycle Flashcards
What is the difference between normal and cancerous cells?
normal cells
- replicate to increase numbers
- regulated balance between growth and death
- growth is maintained by growth systems = controlled
cancerous cells
- mutations can cause the systems to fail
- balance between growth and death is disrupted
- cells divide unchecked = uncontrollable
What are mutations? What are mutations in the cell cycle?
mutations alter DNA
alter the signalling cascades that control cell growth
alters the cell’s ability to function correctly
- proteins do not work the way they should
- systems in place to keep division regulated are lost
- cells grow without restraint
mutations in the cell cycle result in a loss of the regulatory function
What are the 4 characteristics of cancer cells?
survive
- evade body surveillance, are not removed
develop alone
- flourish and are able to grow away from the primary site = spread
feed
- divert blood supplies to bring in food
grow
- stimulate intrinsic growth signals
What are the different stages of the cell cycle?
G1, S, G2 = are interphase
M = mitosis - prophase, metaphase, anaphase, telophase
proceeds sequentially = must go from G1 to S to G2 then M
What happens during G1? S? G2? M?
G1
- materials required for DNA synthesis are prepared = enzymes
- organelles are replicated = cell increases in size, growth phase
S
- duplication occurs = DNA is replicated
G2
- proofing of the new DNA strand = check chromosome alignment, spindle fibre integrity, errors in DNA
- preparation for cell splitting = organelles and proteins develop in preparation of splitting
M
- mitosis (PMAT) followed by cytokinesis
- forms 2 identical daughter cells
What is E2F? What is its function?
E2F is a transcription factor
- target genes of E2F encode proteins required for DNA replication
= proteins such as DNA polymerase, nucleotides
default setting is off due to the bound pRb
- pRb = retinoblastoma protein
- hypo-phosphorylated pRb is complexed to E2F turning it off
What is pRb? What is its function?
pRb is retinoblastoma protein
- inhibits the E2F transcription factor by being complexed to it
- must be phosphorylated to release E2F
- is phosphorylated by cyclin D-CDK4
What are CDK-cyclins? What is their functions?
CDK cyclins = cyclin dependent kinases are enzymes
regulate the cell cycle
- initiate transcription factors by phosphorylating pRb
- phosphorylation of pRb causes it to release the transcription factors and turns them on = gives the go signal
What are the CDK inhibitors?
CDK inhibitors are
- p15, p16, p27 and p21
p53 activates p27
these inhibit CDK cyclins
- prevents phosphorylation of pRb
- transcription factors are not turned on
What is the difference between the checkpoints in G1 and S vs G2 and M?
G2 and M
- have fewer checkpoints
- at this point in the cycle, the cell is assumed to be correct and ready for cell division
faults at these stages tend to be terminal
- cell must be destroyed and are dealt with by mitotic machinery
What is mitotic catastrophe?
if there are any faults in the DNA
- the chromosomes will not align themselves
- the chromosomes will not pull apart properly or the spindle fibres will not connect
What is the G0 phase? What are the features of cells in G0?
quiescence
- cell cycle is normally largely associated with cell proliferation (division) but at G0 the cells are dormant
- dormant cells are not dividing or preparing to divide
cells in G0
- contain one set of DNA
- no active division
- resistant to death = because it is not dividing
- makes up the bulk
- can re-enter the cycle
can be a temporary or permanent state for cells
- temporary = may start division if the correct signals are received
What causes cell proliferation?
loss of control over the cell cycle
- regulatory checkpoints are lost
example
- decreased p15 (CDK inhibitor) results in increased cyclin D and proliferation as a result
How can drugs target and stop the growth of cancerous cells?
anti-proliferative
- stops the go signal initiating the cell cycle
anti-metabolite
- disrupts DNA synthesis
cytotoxic
- kills the cells = cannot discriminate between normal and cancerous cells so kills any cell going through the cycle
