The Cell Cycle And Its Regulations Flashcards
Define cytokinesis
Cytoplasmic division following nuclear division resulting in two new daughter cells.
Define interphase
Phase of a cell cycle where the cell is not dividing it is subdividing into growth and synthesis phases
Define mitosis
Type of nuclear division that produces daughter cells genetically identical to each other and to the parent cell
What are the two main checkpoints?
G1/S checkpoint (restriction point)
G2/M checkpoint
What are the purposes of checkpoints?
Prevent uncontrolled division that would lead to cancer.
To detect and repair damage to DNA (damage caused by UV light)
Cycles cannot be reversed
DNA is only duplicated once during each cell cycle
What is apoptosis?
Programmed cell death
What is senescence?
Where they can no longer divide
Role of M phase
A checkpoint chemical triggers condensation of chromatin.
Halfway through the cycle, the metaphase checkpoint ensures that the cell is ready to complete mitosis.
Events within M phase
Cell growth stops
Nuclear division (mitosis)
Cytokinesis (cytoplasmic division)
Role of G0 phase
A resting phase triggered during early G1 at the restriction point by a checkpoint chemical.
Some cells e.g. epithelial cells lining the gut, do not have this phase.
Events within G0 phase
Cells may undergo apoptosis, differentiation, or senescence.
Some types of cells (e.g.neurones) remain in this phase for a long time/forever.
Role of G1 (growth) phase
A G1 checkpoint control mechanism ensures that the cell is ready to enter the S phase and begin DNA synthesis.
Events within G1 phase
Cells grow and increase in size
Transcription of genes to make RNA occurs.
Organelles duplicate .
Biosynthesis e.g. protein synthesis
The p53 (Tumour suppressor) gene helps control this phase.
Role of S (synthesis) phase
Because the chromosomes are unwound and the DNA is diffuse, every molecule of DNA is replicated.
What is the specific sequence of the replication of genes in S phase?
Housekeeping genes - those which are active in all types of cells are duplicated first.
Genes that are normally inactive in specific types of cells are replicated last.
Events within the cell
Once the cell has entered this phase, it is committed to completing the cell cycle.
DNA replicates.
When all chromosomes have been duplicated each one consists of a pair of identical sister chromatids.
Phase is rapid and because the exposed DNA base pairs are more susceptible to mutagenic agents, reduced chances of spontaneous mutations happening.
Role of G2 phase
Special chemicals ensure that the cell is ready for mitosis by stimulating proteins that will be involved in making chromosomes condense and in formation of the spindle.
Events in G2 phase
Cells grow
