Protein Control Of Cell Division Flashcards
What is a cytoskeleton and what is its function ?
The cytoskeleton is a network of proteins through the membrane , it’s also re forming (dynamic)
It gives mechanical support to a cell
What are cytoskeletons proteins made of ?
Microtubules
Where are microtubules found and what are they made of
Micro tubules are found in all eukaryotic cells
Microtubules are hollow cylinders composed of the protein (globular)tubulin. They radiate from the microtubule organising centre (MTOC) or centrosome.
What is the function of microtubules
They control the movement of membrane bound organelles and chromosomes
What does cell division involve ?
Remodelling of the cytoskeleton
Formation and breakdown of microtubules involves polymerisation and depolymerisation of tubulin
Microtubules form the spindle fibres that are active during cell division
What different processes are in the cell cycle ?
Consists of the interphase and mitotic phase
Why is the cell cycle important ?
It’s required for the growth and repair
Describe the Inter phase?
It consists of 3 phases
G1
S phase
G2
Interphase involves growth and DNA synthesis including G1, a growth phase(proteins and organelles are made ); S phase, during which the DNA is replicated; and G2, a further growth phase(proteins and organelles are synthesised)
Describe the mitotic phase ?
At the end of the G2 a cell enters the mitotic phase
It is divided into 2 stages , mitosis and cytokenises
In mitosis the chromosomal material is separated by the spindle microtubules. This is followed by cytokinesis, in which the cytoplasm is separated into two daughter cells.
What are the 4 stages of mitosis ?
- Prophase
- Metaphase
- Anaphase
- Telophase
Describe what goes on during the prophase
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.
Describe the metaphase?
Metaphase — chromosomes are aligned at the metaphase plate (equator of the spindle)
Describe the anaphase ?
Anaphase — as spindle microtubules shorten by depolymerisation, sister chromatids are separated, and the chromosomes are pulled to opposite poles.
Describe the telophase ?
Telophase — the chromosomes decondense and nuclear membranes are formed around them.
Function of the microtubules in the cell cycle ?
Aligning chromosomes to the metaphase plate
Separating sister chromatids
Formation of daughter nuclei
Control of the cell cycle how does this happen ? And why is this control important
This control is important because timing and rate of cell division is very important , this will vary with different cell types
The control happens through checkpoints , Checkpoints are 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.
Name the different checkpoints?
G1 checkpoints - sufficient cell growth must have happened before it goes to the S phase
G2 checkpoint- success of DNA replication is assessed
M checkpoint- occurs during the metaphase and controls entry to the anaphase , checks if chromosomes are aligned properly, makes sure the daughter cell has the right amount of chromosomes
Describe the G1 checkpoint
G1 is the most important
If a cell doesn’t get a go signal it will undergo G0 phase which is not dividing , if the signal is go then…
At the G1 checkpoint, retinoblastoma protein (Rb) acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication
Phosphorylation by G1 cyclin-CDK inhibits the retinoblastoma protein (Rb). This allows transcription of the genes that code for proteins needed for DNA replication. Cells progress from G1 to S phase.
Describe the G2 checkpoint?
At the G2 checkpoint, the success of DNA replication and any damage to DNA is assessed
When DNA is damaged it activates the activation of several proteins including p53 , this can stimulate DNA repair , arrest the cell cycle or cause cell death
Describe the M checkpoint?
metaphase checkpoint controls progression from metaphase to anaphase, 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 happen if cell cycle rate is not controlled ?
May cause the formation of degenerate diseases
An uncontrolled increase in the rate of the cell cycle may result in tumour formation
What happens when tumours are formed?
A proto-oncogene is a normal gene ,usually involved in the control of cell growth or division, which can mutate to form a tumours promoting oncgene
Describe apoptosis ?
Apoptosis is triggered by cell death signals that can be external or internal
How do external death signals work ?
External death signal molecules bind to a surface receptor protein and trigger a protein cascade within the cytoplasm
Example -production of the signals from lymphocytes
Describe internal death signals ?
An internal death signal resulting from DNA damage causes activation of p53 tumour- suppressor protein
Extra facts
Both types of death signal result in the activation of caspases (types of protease enzyme) that cause the destruction of the cell
Why is apoptosis important?
It is important during development of an organism , as they remove cells that are no longer required in development or during metamorphosis
Or they can do it in the absence of growth factors
