Unit 1: KA5 - Protein Control of Cell Division Flashcards
What is the cytoskeleton?
The cytoskeleton is a network of protein fibres inside the cell. It’s function is to provide mechanical support and shape to cells.
What is the cytoskeleton made of?
Different protein structures including microtubules (in eukaryotes).
What are microtubules?
Hollow cylinders composed of protein tubulin.
What is the function of microtubules?
They control the movement of membrane bound organelles and chromosomes.
What does microtubules’ formation and breakdown involve?
polymerisation and depolymerisation
What does cell division require?
remodelling of the cytoskeleton
What are spindle fibres?
When the cytoskeleton is remodelled, the disassembled microtubules form the spindle fibres.
What function do spindle fibres perform?
The spindle fibres control the movement of chromosomes during mitosis.
What are the two phases of the cell cycle?
- Interphase
- Mitotic phase
What are the stages within the mitotic phase?
Prophase Meta phase Anaphase Telophase Cytokinesis
Describe prophase.
- DNA condenses into chromatid pairs
- Nuclear membrane breaks down
- Spindle microtubules extend from centrosome to attach to chromosomes
What is the centrosome?
Microtubules radiate from the microtubule organising centre (MTOC) or centrosome.
Describe metaphase.
- Chromosomes line up at the metaphase plate (equator).
Describe Anaphase.
- Spindle microtubules shorten by depolymerisation
- Sister chromatids are separated and the chromosomes are pulled to opposite poles.
At what point do spindle fibres attach to chromosomes?
The kinetochore
Describe Telophase
- Nuclear membrane forms around chromosomes
- Chromosomes begin to uncoil (decondense).
Describe cytokinesis
- Separation of the cytoplasm to form 2 identical daughter cells.
What is progression through the cell cycle regulated by?
Checkpoints
What are the 3 sections of interphase, and describe them
G1 - Growth: growth of proteins and organelles
S - Synthesis: DNA replication
G2 - Growth: growth of proteins and organelles
What proteins are involved in regulating the cell cycle?
cyclins
What does the Retinoblastoma protein do?
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 .
How is Rb deactivated?
phosphorylation by G1 cyclin-CDK
What is assessed at the G2 checkpoint?
Success of DNA replication
damage to DNA
What is G₀?
If the cell does not pass the G1 checkpoint, it enters G₀, a resting phase.
What is CDK?
Cyclin Dependent Kinase.
What may an uncontrolled increase in the rate of the cell cycle result in?
Formation of a tumour
What may an uncontrolled reduction in the rate of the cell cycle result in?
a degenerative disease
What 3 checkpoints are there?
G1
G2
Metaphase
Name the protein that is activated by DNA damage.
p53
What 3 things can p53 do after identification of cell damage at the G2 checkpoint.
- Stimulation of DNA repair
- Cause cell death
- Arrest of cell cycle
What does the metaphase checkpoint assess?
Ensure chromosomes are aligned correctly on metaphase plate and attached to the spindle microtubules.
Define the term proto-oncogene
A proto-oncogene is a normal gene that is involved in the control of cell growth or division.
Describe the effects of a mutation within a proto onco-gene.
formation of a tumour promoting oncogene.
Define the term apoptosis.
Apoptosis is the carefully controlled destruction of cells.
How is apoptosis triggered?
Internal or external death signals
What two processes are apoptosis required in?
- Development of an organism
- metamorphosis
Describe how external death signals work and give an example of a molecule that produces one.
Death signals can be produced by lymphocytes
These signal molecules bind to receptor proteins on surface of cell and trigger a protein cascade of caspase proteins
What is caspase?
A type of protease that causes the destruction of the cell by triggering degradation of any protein.
Describe the internal pathway of apoptosis.
A death signal is created and activates p53.
Cells may initiate apoptosis in the absence of growth factors.
Give examples of internal death signals
- DNA damage activates p53
- absence of growth factors
