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The cell cycle & its regulation - Coggle Diagram
The cell cycle & its regulation
cells reproduce by duplicating their contents & then splitting into 2 daughter cells
G0 phase
resting phase triggered during early G1 by the checkpoint chemical
cells may undergo apoptosis, differentiation, senescence
cells may enter a permanent or temporary G0 phase during early G1, where they may under go;
apoptosis
programmed cell death - done when something is wrong with the cell (e.g. DNA mutation)
senescence
cells no longer divide - when they have reached their Hay flick limit (the max num of times a cell can divide)
differentiation
specialised cells
cells that remain in G0 for long time or indefinitely
neurons, nerve cells, egg cells
specialised cells
all cells have ability to divide, but some lose this ability. Specialised cells often go through the cell cycle only once
e.g. neurons, once formed cannot divide again
G1 phase (first growth phase)
cell 'grows'/increases in size
proteins synthesis - enzymes for DNA replication (in S phase) are made
most organelles duplicate
volume of cytoplasm increases
cell differentiation (switching on or off of genes)
if cell is not going to divide again it remains in this phase
G1 + S + G2 = Interphase
interphase - phase of cell cycle where the cell is not dividing: it is subdivided in to growth (G1 & G2) & synthesis (S) phases
S phase (synthesis phase)
DNA replication - this must occur if mitosis is to take place
when chromosomes are duplicated each one consists of a pair of chromatids
this phase is rapid to decrease the chance of spontaneous mutations occurring (exposed DNA base pairs are more susceptible to mutagenic agents)
once cell has entered S phase it is committed to completing the cell cycle
G2 phase (second growth phase)
short gap before mitosis
cell produces the proteins required to cause chromosomes to condense
cytoskeleton of cell breaks down& the protein microtubule components begin to reassemble into spindle fibres - required for cell division
cell division (nuclear & cytoplasmic) takes up 5-10% of the cell cycle
cell cycle length varies for different cell types (minutes to hours to longer)
mitosis
= type f nuclear division that produces daughter cells genetically identical to each other & to the parent cells
cytokinesis
cytoplasmic division following nuclear division, resulting in 2 new daughter cells
Regulation of the Eukaryotic cell cycle - Checkpoints
G1/S checkpoint (aka restriction point)
checks for;
cell size
suitable nutrience
suitable growth factors
DNA damage
once the cell passes through the G1/S checkpoint & enters the S phase it becomes irreversibly committed to division
G2/M checkpoint
determines whether a cell is ready to enter mitosis
checks for DNA damage
Metaphase checkpoint
checks weather the chromosomes are attached to the spindle fibres
purpose of cell cycle checkpoints;
2) to detect & repair damage to DNA (e.g. caused by UV light)
3) to ensure that the cycle can't be reversed
1) to prevent uncontrolled division (could lead to tumours)
4) to ensure DNA is only replicated once during each cycle
Proto-oncogenes & Tumour Suppressor genes
proto-oncogenes
help regulate cell division by coding for proteins that help regulate cell growth
if they mutate that may become oncogenes which can cause cells to fail to undergo apoptosis & instead keep dividing leading to tumours
p53 gene
important as triggers G1/S (restriction point) & the G2/M checkpoints
hence called tumour suppressor gene as helps prevent uncontrolled division
other cell regulatory proteins;
Cyclins
are synthesised in response to cell-signalling molecules such as growth factors
CDHs (cyclin-dependent kinases)
Benign
not cancer
tumorous cells grow locally & cannot spread by invasion or metastasis
Malignant
cancer
cells invade neighbouring tissue
Division of yeast cells
divide by budding
1) Interphase (G1, S, g2) & organelles are replicated
2) set of duplicated chromosomes undergo mitosis so each set of chromosomes is contained within a nucleus
3) a bud forms at surface of cell & one daughter nucleus migrates into the bud
4) bud increases in size & eventually separates from parent cell - producing genetically identical yeast cell
nuclear envelop remain intact
daughter cells are genetically identical but not equal in size
Prokaryotic cell cycle - bacteria
divide by binary fission
can complete cell cycle up to every 20mins in correct conditions
1) bacterial cell grows to its limit (elongates), circular DNA & any plasmids are replicated
2) both copies of DNA then attach to the cell membrane
3) cell membrane begins to grow between the 2 DNA molecules & divided cytoplasm in two
4) new cell wall forms, diving the original 2 into identical daughter cells
Prokaryotic cell cycle - viruses
viruses are non-living particles so they cannot undergo cell division by themselves
1) viruses attach to host cell using attachment proteins
2) inject nucleic acid (DNA or RNA) into host cell
3) host cell then produces proteins from viral genetic information which are assembled into new viruses
