Protein Control of Cell Division Flashcards
What is the purpose of the cytoskeleton?
It 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 do the microtubules radiate from?
The microtubule organising centre (MTOC) or centrosome
What do microtubules do?
control the movement of membrane-bound organelles and chromosomes
What do microtubules form that are active during cell division?
spindle fibres
What does the formation and breakdown of microtubules involve?
polymerisation and depolymerisation of tubulin
What does interphase involve?
growth and DNA synthesis
What phases does interphase include?
G1, S phase and G2
What is G1?
a growth phase
What happens during S phase?
The DNA is replicated
What is G2?
Further growth phase
In mitosis, what separates the chromosomal material?
The spindle microtubules
What is separation of the chromosomal material by spindle microtubules followed by?
cytokinesis
What is cytokinesis?
The process where the cytoplasm is separated into two daughter cells
What are checkpoints?
Mechanisms within the cell that assess the condition of the cell during the cell cycle
What do checkpoints do?
Halt progression to the next phase until certain requirements are met
When do cyclin proteins accumulate?
during cell growth
What do cyclins do?
regulate the cell cycle
What do cyclins combine with and activate?
cyclin-dependent kinases (CDKs)
What do active cyclin-CDK complexes do?
phosphorylate proteins that regulate progression through the cycle
At G1 checkpoint what does the retinoblastoma protein (Rb) act as?
A tumour suppressor; it inhibits the transcription of genes that code for proteins needed for DNA replication
What does the phosphorylation by G1 cyclin-CDK do?
Inhibits the Rb
What does the inhibition of Rb allow?
transcription of the genes that code for proteins needed for DNA replication
What does inhibition of Rb enable?
the cells to progress from G1 to S phase
What happens at G2 checkpoint?
the success of DNA replication and any damage to DNA is assessed
What happens if any DNA damage is identified?
The activation of several proteins including p53 is triggered
What does p53 do?
It can stimulate DNA repair, arrest the cell cycle or cause cell death
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 uncontrolled increase /reduction in the rate of the cell cycle cause?
tumour formation i.e cancer and degenerative disease i.e alzheimers
what do proto-oncogenes do?
usually involved in the control of cell growth or division
Proto-oncogenes can mutate to form….
tumour-promoting oncogenes
What can apoptosis be triggered by?
cell death signals that can be external or internal
Example of external death signal?
The production of death signal molecules from lymphocytes
Example of an internal death signals?
DNA damage
What do external death signal molecules do?
Bind to a surface receptor protein and trigger a protein cascade within the cytoplasm
What does an internal death signal do?
causes activation of p53
What do both death signals activate?
caspases that cause the destruction of the cell
When is apoptosis essential?
during development of an organism to remove cells no longer required as development progresses or during metamorphosis
Why does apoptosis occur?
It removes cells no longer required as development progresses or during metamorphosis
When may cells initiate apoptosis?
in the absence of growth factors
What is apoptosis?
programmed cell death
What are caspases?
a family of protein digesting enzymes
