Cell Cycle & Control of Cell Cycle Flashcards
Why is cell division important?
It allows organisms to grow and develop and replace cells to repair tissues.
Describe the stages in interphase and what happens in each one.
G1 - The first growth stage where the cell makes new proteins and copies of organelles.
S - DNA replication.
G2 - The second growth stage.
What are the stages of the M phase in order?
Prophase, Metaphase, Anaphase, Telophase, Cytokineses.
Describe what happens in Prophase.
1) The replicated chromosomes condense (get shorter and fatter) and appear as sister chromatids preparing to be moved.
2) The cells microtubules start to disassemble from the centosomes which move to opposite poles. The microtubules start forming the spindle fibres and astars and some microtubules are attached to the kinetochore proteins.
3) The kinetochore proteins attached to the centromeres of the chromosomes have tension-sensitive proteins which allows them to ensure each chromatid is attached to each centrosome.
4) The nucleur membrane starts to break down.
Describe what happens in Metaphase.
Multiple spindle fibres become attached to each chromatid which are then alligned at the equator of the spindle fibres, called the metaphase plate.
Describe what happens in Anaphase.
1) The kinetochore end of the spindle fibres are quickly disassembled which causes the sister chromatids to speparate. They are now called individual chromosomes.
2) The spindle fibres attached to each of the chromosomes shorten to pull them to opposite poles of the cell.
Describe what happens in telophase.
1) Each chromosome arrive at the cell poles and unravel.
2) A new nucleur membrane is formed around each group of chromosomes to form two daughter nuclei.
What is cytokineses?
Cytokineses is the division of the cytoplasm to form two new daughter cells
Why is it important to control the cell cycle and what would happen if:
a) there is an uncontrolled reduction in rate of cell cycle.
b) There is an uncontrolled increase in the rate of cell cycle.
- It is important to control the rate of the cell cycle to ensure new cells are produced at the correct rate and in the right place.
- An uncontrolled reduction in the rate of the cell cycle could result in a degenerative disease such as Alzheimers.
- An uncontrolled increase in the rate of the cell cycle could result in the formation of a tumour.
Describe the G1 checkpoint.
This checkpoint is near the end of G1 and it monitors the cell size as there must be a sufficient cell mass to form two daughter cells. If the go-ahead signal is reeached the cell can continue and replicate DNA, if it isn’t reached the cell might switch to a resting stage called G0. If the conditions change, the cell can re-enter the cycle.
Describe the G2 checkpoint.
This checkpoint occurs at the end of the G2 phase and it assesses the completion of DNA replication to ensure each daughter cell will recieve a complete copy of DNA. If the go-ahead signal is reached the cell will move onto the M phase.
Describe the M checkpoint.
Occurs during metaphase and monitors the chromosome allignment and attachment to spindle fibres to ensure each daughter cell recieves one chromtid from each chromosome.
What are CDK’s and what role do they play in the G1 checkpoint?
CDK’s combine with cyclin proteins which accumulate during G1 and this binding activates the CDK. Active CDK’s cause the phophorylation of target proteins (Retinoblastoma protein) that stimulate the cell cycle. If enough phosphorylation is done, the check-point allows the cell to continue and if there is not sufficient phosphorylation done, there will be a stop signal and the cell may enter G0.
What is Retinoblastoma protein (Rb) and what is its role in controlling the cell cycle?
- Rb is an inhibitor for the transcription factors involved in the production of proteins required for DNA replication in the S stage. When there are low levels of CDK activity, Rb binds to transcription factor E2F and this binding inhibits the transcription of genes needed to enter the S stage. This inhibition is the molecular stop signal for the checkpoint.
- Rb is released from factor E2F when it is repeatedly phosphorylated by CDK, allowing the genes required for DNA replication to be transcribed. Phosphorylation of Rb gives the go-ahead signal.
What is the p53 protein and what does it do?
The p54 protein is another part of the G1 checkpoint. It is a transcription factor that can stimulate the repair of DNA, pause the cell cycle or trigger apoptosis.
