1.5: protien control of cell division Flashcards
what is the cytoskeleton
a fibrous framework that gives mechanical support and structure to a cell
what are cytoskeletons made from
consist of different protein structures including microtubules found in all eukaryotic cells
what are microtubules
hollow rods composed of the protien tubulin
what do microtubules do
control the movement of membrane bound organelles that are attached to them and the movement of chromosomes during cell division
what causes the change in size of microtubules
polymerisation and depolymerisation
what does cell division require
remodelling of the cytoskeleton
what do microtubules form
form the spindle fibres active during cell division
what are the two phases of the cell cycle
interphase and miotic phase
what does the miotic phase involve
mitosis and cytokenesis
what are the three phases of interphase
G1 ( growth phase), S( DNA replication occurs), G2(further growth phases in prep for mitosis)
what is mitosis
chromosomal material is separated by spindle microtubules
what is cytokenesis
cytoplasm is separated into two daughter cells
what does mitosis consist of
mitosis consists of prophase, metaphase, anaphase and telophase
what occurs during prophase
DNA condenses into chromosomes containing two sister chromatids. The nuclear membrane breaks down and spindle fibres extend from the MTOC by polymerisation and attach to the chromosomes via centromere regions
what occurs during metaphase
the chromosomes align at the metaphase plate
what occurs during anaphase
spindle microtubules shorten and pull sister chromatids apart to opposite poles
what occurs during telophase
chromosomes decondense and new nuclear membranes are formed around them
how is progression of cell cycle controlled
controlled by checkpoints
what are cell checkpoints
mechanisms within the cell that assess its condition during the cell cycle and halt progression to the next phase unless requirements are met.
what are cyclin protiens
proteins that accumulate during cell growth and are involved in regulating the cell cycle
what do cyclins combine with
cyclin-dependant kinases
wat do active cyclin-CDKs do
phosphorylate proteins that regulate the progression throughout the cycle.
what occurs at the G1 checkpoint
sell size and mass if checked. retinoblastoma acts as a tumour suppressor by inhibiting transcription of genes needed for DNA replication, however the cyclin-CDK inhibits the Rb and allows transcription to occur. cells then progress to stage S
what inhibits retinoblastoma
cyclin-dependant kinase
what does the inhibition of Rb allow
transcription of proteins needed for DNA replication
what occurs at the G2 checkpoint
assess success of DNA replication and any damage to DNA, cells will progress to M and undergo mitosis
what is the role of p53
stimulate DNA repair, arrest the cell cycle or cause cell death
what does DNA damage trigger
p53
what occurs at the metaphase checkpoint
controls progression from metaphase to ananphase
why is progression halted at the metaphase checkpoint
to ensure chromosomes are aligned correctly on metaphase plate and are securely attached to spindle microtubules
why should cell cycle be controlled
it has to be controlled to ensure daughter cells are produced at correct rate and place
what does an uncontrolled decrease cause
a degenerative disease such as Alzheimer’s
what does an uncontrolled increase cause
a build of cells causing tumour formation
what are oncogenes
normal gene, usually involved in control of cell growth or division that can mutate to form a tumour forming protein
what is apoptosis
is the controlled death of cells, programmed cell death that can occur during normal growth or development that results in the removal of old or damaged cells
what is an extrinsic signal
a death signal that occurs from outside the cell
what is an intrinsic signal
a death signal that occurs within the cell
what do extrinsic signals do
extrinsic signal molecules bind to a surface receptor protein and triggers a protein cascade within the cytoplasm
what is an example of an extrinsic death signal
death signal molecules from lymphocytes
what do intrinsic signals do
can be caused by DNA damage which causes a disruption of the integrity of the mitochondria which triggers a cascade
what do both death signals result in
result in activation of protease enzymes called caspases which act in cascades to cause destruction of the cell
when is apoptosis essential
to remove cells no longer required
why do cells initiate apoptosis
may be because of an absence of growth factors
what is the MTOC
it is the microtubule organising centre and microtubules radiate from here
what happens if go-ahead signal is not reached at checkpoint G1
may switch to a non dividing or resting state called G0
what is also assessed at checkpoint G1
DNA damage, can trigger the activation of several proteins including p53
