5c + 5d: Control of the Cell Cycle Flashcards
Why are checkpoints important
To regulate the progression through the cell cycle
What are checkpoints
Mechanisms within the cell that assess the condition of the cell during the cell cycle and halt the progression to the next phase until certain requirements are met.
What are the cell cycle checkpoints
G1, G2, M
What are cyclin proteins
Cycling proteins accumulate during the cell growth are involved in regulating the cell cycle
What do cyclins do
Cyclins combine with and activate cyclin- dependant kinases (CDKs)
Active cyclin- CDK complexes phosphorylate proteins that regulate progression through the cycle
if sufficient phosphorylation is reached, progression occurs
What is the G1 checkpoint
retinoblastoma (Rb) protein acts as a tumour suppressor by inhibiting the transcription of genes that code for proteins needed for DNA replication.
G1 cyclin-CDK phosphorylase’s the Rb protein. The phosphorylation inhibits Rb. This allows for the transcription of genes that code for proteins needed for DNA replication. Cells can progress from G1 to S.
What is the G2 checkpoint
Assesses the success of DNA replication and any damage to DNA is assessed.
What does DNA damage trigger
The activation of several proteins including p53
What can p53 do
- stimulate DNA repair
- arrest the cell cycle
- cause cell death (initiate apoptosis)
What is the metaphase checkpoint
Controls the progression from metaphase to anaphase.
Progression is halted until the chromosomes are aligned correctly on the metaphase plate and attached to the spindle microtubules.
The uncontrolled cell reduction can result in….
A degenerative disease (eg Alzheimer’s)
an uncontrolled increase in the rate of the cell cycle may result in..
Tumour formation.
What is proto-oncogene
Is a normal gene, usually involved in the control of cell growth and division, which can mutate to form a tumour promoting oncogene.
What is apoptosis
The destruction of cell. Programmed cell death.
What is apoptosis triggered by
Cell death signals that can be external or internal.
External death signals example
Production of death signal molecules from lymphocytes.
How do eternal cell death signals work
External death signal molecules bind to a surface receptor protein and trigger a protein cascade within the cytoplasm.
Internal cell death signal example
Eg DNA damage causes activation of p53 tumour suppressor proteins
Both types of death signal results in the activation of…
Caspases
What are caspases
Types of protease enzyme which cause the destruction of the cell
Other conditions which initiate apoptosis
absence of growth factors
Importance of apoptosis
Apoptosis is essential during development of an organism to remove cells no longer required as development progresses or during metamorphosis.
