Cell Cycle Flashcards
What is the aim of the cell cycle?
To produce 2 daughter cells, with a set of chromosomes identical to the parent cell.
What are the phases of the cell cycle?
- G0
- G1
- S
- G2
- Mitosis
- Cytokinesis
What occurs in the G0 phase?
This is the phase when cells are not actively dividing (quiescence).
This stage is permanent in some cells (erythrocytes).
It is a response to an external signal/mitogenic factor.
(B and t lymphocytes are an example of cells that can enter and re-enter this stage.
What occurs in the G1 phase?
Cells grow in size and synthesize RNA, proteins and other proteins and molecules needed for preparation for S phase. The restriction point checkpoint and DNA damage checkpoints are present in the G1 and late G1 phases respectively. Around 11hrs.
What do checkpoints check for?
They check for:
- favourable external environments for cell divion (presence of growth factors)
- favourable internal environments (sufficient growth)
- DNA damage
- Replication errors
- Spindle damage
- Chromosome integrity
What happens in the restriction point checkpoint?
Cell cycle progression is determined by the presence of growth factors that G1 phase detects. This is the point at which it commits to cell division.
This checkpoint depends on the accumulation of cyclin D-CDK4/6 complex.
Rb acts as the gatekeeper as as it inhibits E2F and when enough growth factors are created the CDK-cyclin molecule is made, this will phosphorylate the Rb protein, allowing the E2F to transcribe genes for the S phase.
What does the DNA damage checkpoint do?
There are 2, one at late G1 and one at late G2
This checkpoint monitors damage to DNA:
chemical mutagens, radiation and errors in replication.
It works as p53 detects damage and produces CKI’s p21, this is a transcription factor that directly transcribes genes to arrest cell cycle (for small DNA damage).
For large DNA damage it transcribes genes for apoptosis.
What CDK-Cyclin molecules relate to the DNA damage checkpoints?
CDK2-cyclin E/A at late G1 phase
CDK1-cyclin A/B at late G2 phase
What occurs in the S phase?
Mainly important for DNA synthesis and by the end of it, 4 strands of DNA (2 chromatids) are present. Around 8hrs.
What occurs in the G2 phase?
Used for further growth and cells prepare for mitosis. Around 4hrs.
What are the phases of mitosis?
Prophase Pro-metaphase Metaphase Anaphase Telophase
What happens during the prophase?
- Chromatin condensation
- Nucleolus dissapears
- Centrioles move to poles
What happens during pro metaphase?
- Nuclear membrane dissolves
- chromosomes attach to microtubules and begin moving
What happens during metaphase?
-Spindle fibres allign the chromosomes along the middle of the cell nucleus (metaphase plate).
There is also a checkpoint here and anaphase promoting complex (APC) is inhibited until all chromosomes are attached.
What happens during anaphase?
Paired chromosomes seperate and move to opposite sides of the cell.
