the asexual cell cycle

G1

• cell increases in sizze

• ribosomes, RNA produced and preparation for DNA synthesis

S

• DNA synthesised

G2

• cell checks the fidelity of DNA and prepares for nuclear divisions (+more cell growth)

G0

• occurs sometimes, where the cells are inactive ‘quiescent’

what happens to the DNA during interphase?

• the chromosome in S-phase forms 2 sister chromatids

• during mitosis, the chromosomes segregate and the overall amount of DNA ends up the same

prophase

• chromosomes condense so they are now visible

• sister chromatids are held togethwe by a protein called cohesin

• later in prophase, the nuclear membrane breaks down (also called prometaphase)

the mitotic spindle

• cytoskeletal structure, largely made of microtubules (polymers of small tubulin protein subunits)

• the spindles separate sister chromatids into different daughter cells

• this happens because the microtubules contract to pull chromosomes towards the pole

kinetochores

• large protein complex that connects that centromeres to microtubules

metaphase

• centromeres align at the spindle equator- midway between the 2 poles

• microtubules attach to each pole- tension between these keeps chromosomes in the centre

anaphase

• sister chromatid cohesin breaks down

• chromatids become separate chromosomes

• centromeres start moving to opposite poles

• depending on the centromere- each chromosome can form a V shape as it is dragged behind the centromere

telophase

• chromsomes arrive at the cell poles

• chromsomes decondense- no longer visible thread-like structures

• daughter nuclei reform

cytokinesis

• division of the rest of the cellow

• cleavage furrow (animals) or cell plate (plants) forms in-between the 2 poles

• constriction to give 2 daughter cells

• can be symmetrical or give 2 uneevenly shaped daughter cells (budding yeast)

bidge chromosome

• a chromosome that erroneously has 2 centromeres is pulled towards both poles at once. Ends up being broken

acentric chromosome

• lacking a centromere, unable to segregate properly

asynchronous population/ lenght of stages