The Cell Cycle Flashcards
The cell cycle
An ordered series of event that lead to division of a cell into two identical daughter cells
M - mitosis
Segregation of chromosomes, followed by division to produce two daughter cells
G1 - gap 1
Increase in cell contents including replication machinery
S - synthesis
Replication of DNA —> chromosomes become two sister chromatids attached to the centromere
G2 - gap 2
Preparation for division process
G0
Cell not going through the cell cycle - arrested at G1
Prophase
- chromosomes condensation
- dispersal of nucleoli
- separation of centrosomes and formation of mitotic spindle
Prometaphase
- fragmentation of the nuclear envelope
- attachment of spindle MTs to centromeres
- chromosomes start to move towards cell centre
Metaphase
Chromosome alignment at metaphase plate
Anaphase
Chromosome (chromatids) move to opposite cell poles
Telophase
- chromosome uncoil
- nucleoli develop and fuse
- disassembly of spindle
- re-formation of the nuclear envelope
Kinetochore MTs
Move chromatids towards centrosome - Anaphase A
Polar and astral MTs
Move poles away from each other (Anaphase B)
What controls the cell cycle
- Ensure processes happen in the right order
- Sense and respond to signals
- Monitor status and take decisions: progress or arrest
Transition point
Cell controls progression of the cell cycle
What do checkpoint pathways do?
Molecular pathways that monitor and stop cycle
G0 —> G1
Growth factor signalling
G1 —> S
Growth factors, nutrients, DNA damage checkpoint
G2 —> M
DNA replication checkpoint; DNA damage checkpoint
M —> G1
Mitotic spindle assembly checkpoint
Mitotic spindle checkpoint
Prevents anaphase from beginning before chromosomes are all attached to the spindle
DNA replication checkpoint
Monitors DNA replication to ensure DNA synthesis is completed before mitosis begins
DNA damage checkpoints
Prevents cell with damaged DNA from proceeding through the cycle unless the damage is repaired
DNA damage checkpoints
- DNA damage activates
- ATM/ATR phosphorylates checkpoint kinase
- Checkpoint kinases phosphorylate p53, detach it from Mdm2 abd stabilize jt
- p53 is a transcription factor
Replicating challenges
- replicating the genetic information with high fidelity
- distributing chromosomes equally between daughter cells
Chromatid cohesion
- each pair of sister chromatids are held together by proteins called cohesins
- the chromatids are held together until ready for separation during late mitosis
Why is chrosome spindle attachment necessary?
For progression at anaphase
What is Cdc20?
A kinase that acts as an activator of the anaphase promoting complex
What do cyclin-CDK complexes do?
Ensure processes happen in the right order
What do external and internal signals do?
Sense and response to signals
What does chromatid cohesion do?
Prevents uncontrolled segregation of replicated chromosomes
