1.5 Protein Control of Cell Division Flashcards
What is the cytoskeleton?
-Network of protein fibres that extends throughout the cytoplasm.
- anchored to proteins in the plasma membrane
- is constantly breaking down and re-forming to allow the cell to change shape.
What are the functions of the cytoskeleton?
- Providing mechanical support so that cell shape can be maintained
- Providing a method of anchoring the organelles of the cell (and some enzymes)
- It can enable the whole cell to move
- It can enable the organelles within a cell to move
What is the cytoskeleton made up of?
Several types of protein including microtubules
What are Microtubles?
Microtubules are around 25nm wide and are hollow, straight cylinders composed of proteins called tubulins.
How is the length of microtubles controlled?
The addition or removal of tubulin at the ends of the microtubles
(polymerisation/ depolymerisation)
What is the role of microtubles
Microtubules are responsible for the location and movement of the membrane-bound organelles and other cell components including chromosomes.
Where do microtubles originate from?
The microtubule-organising centre (MTOC)
Or the centrosome which is located near the nucleus and contains centrioles, which are the site of microtubule synthesis.
Describe the role of microtubles in Cell division
used in remodelling of the cell’s cytoskeleton.
also form the spindle fibres which are active during cell division.
What is the purpose of cell division?
Cell division is a vial process that allows an organism to grow and develop, to replace dead cells and repair tissue.
What are the two stages of cell division?
interphase and the mitotic phase
During the interphase a cell is undergoing…….
a period of growth which involves
- protein synthesis
- creation of the organelles
- the replication of chromosomes
What are the 3 stages of interphase?
G1
S phase
G2
Describe G1
G1 is the first growth/gap phase, during this time proteins and organelles are synthesised
What happens in the S phase
S phase involves the replication of DNA
What happens in G2
G2 is the second growth/gap phase which also involves the synthesis of proteins and organelles.
What are the stages of mitosis?
- Prophase
- Metaphase
- Anaphase
- Telophase
Describe the events occuring in prophase
- DNA condenses into chromosomes each consisting of two sister chromatids.
- The 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 events occuring in Metaphase
chromosomes are aligned at the metaphase plate (equator of the cell/spindle)
Describe the events occurring in Anaphase
As spindle microtubules shorted (by depolymerisation) sister chromatids are separated and the chromosomes are pulled to opposite poles
Describe the events occurring in Telophase
the chromosomes decondense and the nuclear membranes are formed around them.
What is the final part of the cell cycle?
Cytokinesis
What happens during cytokinesis
Cytoplasm splits to form two daughter cells.
Why must cell be produced at the correct rate and in the correct locations
to allow regulated growth and repair
An uncontrolled reduction in the rate of the cell cycle will result in…..
Because……..
degenerative disease such as Alzheimer’s or Parkinson’s as insufficient replacement cells are being formed for normal tissue function
An uncontrolled increase in the rate of the cell cycle may result in…..
the formation of tumours. Uncontrolled growth may be benign or may result in a malignant cancer
What is a proto-oncogene?
A proto-oncogene is a normal gene that can mutate to form a tumour-promoting oncogene
What is progression of the cell cycle controlled by?
Checkpoints
What types of signalling is used to control the cell cycle
internal and external
Which proteins accumulate during cell growth and what is their role?
Cyclin proteins that accumulate during cell growth are involved in regulating 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
The next stage of the cell cycle will occur if
sufficient phosphorylation is reached
Describe What occurs at the G1 Checkpoint
This occurs towards the end of G1. At this 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 Rb. This allows transcription of the genes that code for proteins needed for DNA replication. The cell can then progress from G1 to S phase.
Describe the G2 Checkpoint
Occurs at the end of G2, the success of DNA replication and any damage to DNA is assessed.
- DNA damage triggers the activation of several proteins including p53 that can stimulate DNA repair, arrest the cell cycle or cause cell death.
Describe the M Checkpoint
- Occurs during metaphase
- controls progression from metaphase to anaphase.
- At this checkpoint, progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules.
Apoptosis is triggered by…..
cell death signals that can be external or internal
How are External death signals transmitted
- External death signal molecules bind to a surface receptor protein
- trigger a protein cascade within the cytoplasm
Describe Internal death signals
Internal death signal resulting from DNA damage causes activation of p53 tumour suppressor protein
Death signals result in……
The activation of caspases (types of protease enzyme)
that cause the destruction of the cell
Why is Apoptosis important?
Removes cells no longer required as development progresses or during metamorphosis
Cells may initiate apoptosis in the absence of….
Growth Factors
