cell cycle- lecture 3

yeast pombe - advantage is that u can see the whole cell cycle in the cell

the reason the gene is called wee 1 is beacuse when cells go through the cell cycle without it they dont gather enough material and therefore they end up getting smaller and smaller - this tells the cell if it has enough material

eukaryotes and yeast are different

cancer celll lines are used to research the cell cycle - thye are seperated with proteases

they will be seperated - the difficulty is that cells have a natural tendancy to get shorter and shorter by the telomers with each replications - the adult cells only get so much replication before they die - in cancer cells - instead of dieing the cells express protease to extend the end of the chromosone and further extend theyre lifespan - the only other cell that can do this is an embryo - the egg can correct the dna

in order to keep the cancer cells alive they need to be kept in feutal bovine serum - serum of the feutus of a cow

most cancer mutations are caused by the epithlial cells because these dont have other cells to tell them to stop replicating and have more contact with their environment

if u strave the cells - ie take away their growth signals - then the cells will delay their cell cycle - unless the cell cycle hass already begun in that case the cell cycle will continue

  • theres about fifty different growth factors - each has its own specifci receptor tyrosine kinase - an OTC

  • growth factpr binds to this membrane protein and a dime arises and it can cross phophorulated self on tyrosien residues

  • cyclin dependent kinases of serine tyrosine

  • this is a tyrosine kinase - different

  • this then interacts with a protein called grab

  • sos protein then interacts with a protein celled ras - ras is bound to gtp

  • there are exchange factors which exchange this gtp and allows the activation of ras

  • this then signals through the cell a cascade of proteins

  • the ultimate target of this cascade are proteins that are involved in accumulating nutrients from the cell medium and also prodcuong the intial proteins that are going to drive the cell cycle

how do we know this pathway is important

mutation in the ras gene - result in most humn cancers

most targeted gene in the pharamceutical section - the undruggable protein

alot of the mutant forms of this gene destroy the ras protiens catalytic actvity

when the ras gene is activated - it binds this gtpmolecules and starts signalling into the cell

if u mutate the ras gene so that it cant hydrolyse the gtp it keeps this signal into the cell going - large number of the mutations are on this active aite

this casade of proteins also serves as an amplification for the cell - oen receptor on the outside is used but then the entire cell knows it has to proliferate

in order to cross the restrciction point of the cell u need the grwoth signals and u need enough nutrients - key target is cyclin d

the grwoth signals can effect numerous points of this they induce the transcription of the cyclin gene they stop it from being degraded they activate the uptake into the nucleus and increasee its association with the CD to a protein

So what's the big deal about cyclin D binding to CDK4, which is set a restriction point- retinoblastoma

retinoblastoma - protein

if you have one mutant form of this gene - you dont get cancer - but if the secind gene gets damaged u get a tumour

if u have two - you get cancer

evidence to show the importance if u mutate cyclin d you get cancer

viruses want ur cell to proliferate - ie hpv causing cervical cancer

hpv has a protein called e7 whihc interacts with retinoblastoma

retinoblastoma can be phosphurulated this releases a protein called e2f this is a transcription factor essential for the prduction of a large amount of genes involved in making the proteins for dna synethsis - ribonucleotidereductase

makes the nucelotides for dna synethsis - measn the cell is gettign ready for s phase and has crossed the restriction points

G0- where the cell leaves the cell cycle permanently - neurons - but if u take the nuerons out and fgive them the right growth factors then u can make them proliferate

the stage G0 is started by cip proteins

mitosis

the best understood of the cell cycle beacuse its so visual

prophase

metaphase

anaphase

telephase

the applications of this - oncology - alot of cancers are caused by chromosone breaks - they get rearranged and u get a new protein called

BCR Able -protein starts geting produced

this is important for diagnosistics

the nuclear membrane and how its dissembled - its a double membrane and its attached to the dna - the insdie has lamina proteins

rna and proteins get in and out through the nucelar pores

so how it breaks down

  • break down of the nucelar pore complex

  • phosphrulation of the laminantes which breaks them down

  • you get ohophrulation of the chromatin proteins which cause them to let vo of their nuclear and exterior

  • any problems with the lamina gives rise to disease callled progeria - massive aging of the body

  • the nucelus is very prone to damage by the mitochondria

laminas

lamina a- free in cytosol

lamina b - inside of membrane normally but ends up on outside forms membrane vesicles

paclaging of the chromsones - packed by histones very conserved accross spieces

cohesive rings - contract so that the dna gets copied

this cohesive rings make sure that the sister chromatids stay attached while theyre moving in the cell to the metaphase

the polo like kinasses and the aurara kinases

serine threonin kinases

controlled by bora

polar like kinsae then activates toher things to kick of mitosis

it inhibits wee one and MIC one whihc inhibt the cell cycle by phosphurlating tyrosine and theronine residues

polar like kinase -activates the CBC 35 phophatase which will remove those inhibtory phosphorylation and it will also phosphurlate cyclin b 1 to increase its activity

this protein - attach green florescent proteins - take to confocal microscope - its starts at the exterior then localised to the central portion of the chromosones then at the microtubales attaching

also at the furrow

has many roles phosphurlating proteins in the cell cycle

it takes alot of effort to seperate of the chromsones - the centriols - these are made of microtubule burrows - the fact theyre attached to the microtubulas - where is the polar like kinase - its with the centroils phosphurlating the aura protein