1.5 Protein Control of Cell Division Flashcards
what does the cytoskeleton do
gives mechanical support and shape to cells
what does the cytoskeleton consist of
different protein structures including microtubules, which are found in all eukaryotic cells
what are microtubules
hollow cylinders composed of the protein tubulin
where are the microtubules found
they radiate from the microtubule organising centre (MTOC) or centrosome
what do microtubules do
control the movement of membrane-bound organelles and chromosomes
what does cell division require
remodelling of the cytoskeleton
what does formation and breakdown of microtubules involve
polymerisation and depolymerisation of tubulin
what do microtubiles form
the spindle fibres that are active during cell division
what does the cell cycle consist of
interphase and mitotic (M) phase
what does the interphase involve
growth and DNA synthesis including:
G1, a growth phase,
S phase, during which the DNA is replicated,
and G2, a further growth phase
what does the mitotic phase involve
mitosis and cytokinesis
what happens in mitosis
the chromosomal material is separated by the spindle microtubules
this is followed by cytokinesis
what happens in cytokinesis
the cytoplasm is separated into two daughter cells
what does mitosis consist of
prophase
metaphase
anaphase
telophase
what is prophase
DNA condenses into chromosomes each consisting of two sister chromatids.
nuclear membrane breaks down.
spindle microtubules extend from the MTOC by polymerisation and attach to chromosomes via their kinetochores in the centromere region
(think pro means before)
what is metaphase
chromosomes are alligned at the metaphase plate (equator of the spindle)
(think middle)
what is anaphase
as spindle microtubules shorten by depolymerisation, sister chromatids are seperated, and the chromosomes are pulled to opposite poles
(think away)
what is telophase
the chromosomes decondense and nuclear membranes are formed around them
(think two)
what is progression in the cell cycle controlled by
checkpoints
what are checkpoints
mechanisms within the cell that assess the condition of the cell during the cell cycle and halt progression to the next phase until certain requirements are met
what is involved in regulating the cell cycle
cyclin proteins that accumulare during cell growth
what do cyclins combine with
they combine with and activate cyclin-dependent kinases (CDKs)
active cyclin-CDK complexes phosphorylate
proteins that regulate progression through the cycle
if sufficient phosphorylation is reached, progression occurs
what happens at the G1 checkpoint
retinalblastoma proteins (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication
what does phosphorylation by G1 cyclin-CDK inhibit
the retinalblastoma protein (Rb)
what does the inhibation of Rb allow
transcription of the genes that code for proteins needed for DNA replication.
cells progress from G1 to S phase
what happens at G2 checkpoint
the success of DNA replication and any damage to DNA is assessed
what does DNA damage trigger
the activation of several proteins including p53
what is p53
it can stimulate DNA repair,
arrest the cell cycle,
or cause cell death (apoptosis)
what does a metaphase checkpoint control
the progression from metaphase to anaphase
what happens at the metaphase checkpoint
progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules
what can an uncontrolled reduction in the rate of the cell cycle result in
degenerative disease
what can an increase in the rate of the cell cycle result in
tumour formation
what is a proto-oncongene
a normal gene, usually involved in the control of cell growth or division, which c an mutate to form a tumour-promoting oncogene
what triggers apoptosis
apoptosis is triggered by cell signals that can be external or internal
what is an example of an external death signal
the production of death signal molecule from lymphocytes
what is an example of internal death signal
DNA damage
what do external death signal molecules bind to
a surface receptor protein and trigger a protein cascade within the cytoplasm
what does an internal death signal resulting from DNA damage cause
activation of p53 tumour-suppressor protein
what do both internal and external death signal result in
the activation of caspases that cause the destruction of the cell
what is caspases
types of protease enzyme
why is apoptosis essential during development of an organism
to remove cells no longer required as development progresses or during metamorphosis
what can happen in the absence of growth factors
cells may initiate apoptosis
