1.5 protein control of cell division Flashcards
what is the cytoskeleton?
a network of proteins extending throughout the cytoplasm, anchored to proteins in the PM
what is the function of the cytoskeleton?
- provide mechanical support so that the cell maintains its shape
- provide anchorage for many organelles
what is the cytoskeleton made of?
several types of protein, including microtubules
what are microtubules?
hollow cylinders made of a protein called tubulin
where are microtubules formed and radiated from?
a centrosome or MTOC (microtubule organising centre)
what is the role of microtubules?
- govern the location and movement of the membrane-bound organelles and other cell components
- form the spindle fibres that are active during cell division
how are spindle fibres formed then broken down?
by polymerisation and then depolymerisation of tubulin
what does cell division allow?
organisms to grow and develop, by regulating the growth and replacement of genetically identical cells
name the two parts into which the cell cycle can be divided
interphase
the mitotic phase
describe interphase
an active period of growth
name the three sub-phases that interphase can be divided into
G1, G2, S
describe G1
a growth period where proteins and organelles are synthesised
what happens during S phase
the cell continues to grow and DNA replication takes place
describe G2
another growth period
what happens after G2
the cell enters the mitotic phase
what happens during the mitotic phase?
mitosis and cytokinesis
what is mitosis?
when the nucleus and contents divide
what is cytokinesis?
the separation of the cytoplasm into daughter cells
what could an uncontrolled reduction in the rate of the cell cycle result in?
degenerative diseases
what could an uncontrolled increase in the rate of the cell cycle result in?
tumour formation
name the 4 stages of mitosis in order
prophase, metaphase, anaphase, telophase
describe the first event of prophase
- DNA condenses into discrete chromosomes with each chromosome consisting of 2 sister chromatids
describe the second event of prophase
- the nuclear membrane breaks down and spindle fibres extend from the centromere via polymerisation
describe the final event of prophase
the fibres then attach to the chromosomes’ centromere at a region called the kinetochore
what happens during metaphase?
the chromosomes line up at the metaphase plate at the centre of the cell
what happens during anaphase?
as spindle microtubules shorten
by depolymerisation, sister chromatids are
separated, and the chromosomes are pulled
to opposite poles
what happens during telophase?
the chromosomes decondense and nuclear membranes are formed around them. cytokinesis also occurs
why must the cell cycle be controlled?
to ensure that events in the cycle proceed in the correct order and that each event is completed before the next starts
how is the cell cycle controlled?
by checkpoints at various stages within the cell cycle
what do checkpoints do?
they asses the condition of the cell and halt the progression onto the next phase until certain that all conditions have been met
what is cyclin?
a protein involved in the regulation of the cell cycle by checkpoints
what do cyclins do?
they combine with active and inactive cyclin-dependent kinases (CDKs) that phosphorylate other proteins which regulate the cycle
what happens when sufficient phosphorylation is reached by CDKs?
progression occurs
what does the G1 checkpoint check before the cell enters S phase?
that cell growth has occurred
what happens if the G1 checkpoint finds that cell growth has not occurred?
the cell switches to G0 phase
what does the G2 checkpoint check for?
that DNA replication has been completed and damage assessed
what does the M checkpoint check before the cell enters anaphase?
that chromosomes are aligned correctly on the metaphase plate and attached to spindle fibres
name the tumour suppressor protein at G1 checkpoint
retinoblastoma (Rb)
what does the Rb protein do?
inhibits transcription of genes that code for proteins needed for DNA replication
what happens at the G1 checkpoint that allows the cell to progress to S phase?
CDKs inhibit the Rb protein via phosphorylation, allowing transcription of the genes that code for proteins needed for DNA replication
what is a photo-oncogene?
a normal gene involved in controlling cell division
what happens when a photo-oncogene mutates?
it becomes a tumour-promoting oncogene, contributing to the development of cancer
apoptosis can be triggered by … signals
internal or external
what is an example of an external signal?
lymphocytes producing death signal molecules
what is an example of an internal signal?
DNA damage
how do external death signal molecules initiate their reaction?
by biding to a surface receptor protein and triggering a protein cascade inside the cytoplasm
how does an internal death signal from DNA damage initiate its reaction?
activates a protein called p53
what do both internal and external death signals result in?
activation of caspases (a type of protease) that cause destruction in the cell
why is apoptosis essential during development?
to remove cells that are no longer required
give an example of when apoptosis might be initiated
in the absence of growth factors
