BMD116A W6 - Cell cycle and cell division

116A WEEK 6 - Cell cycle and cell division

Learning outcomes:
- Principles of the cell cycle and cell division
- The types of cell division
- Mitosis and Meiosis
- Molecular mechanisms involved in cell cycle regulation

Why is cell division important?
- Promotes regeneration and life in general
- Errors lead to aneuploidy and are associated with
cancer
- Highly complicated but highly conserved – how did
it evolve?

Cell cycle and mitosis

G1 Phase
- Aim: recover from M and prepare for S phase
- Gap/Growth Phase 1
- General DNA checking/repair
- Synthesis of RNA and protein
- Generation of new organelles
- Cells increase in size

G0 Phase (during G1)
- “Technically” not part of the cell cycle
- Resting phase
- Terminal differentiation state
(irreversible)
- Quiescent state (stem cells,
reversible)
- Response to stress

S Phase
- AIM: to replicate the genome
- Synthesis phase
- Chromosome duplication
- Centrosome duplication

G2 Phase
- AIM: to prepare for mitosis
- Gap/Growth Phase 2
- Second round of DNA proofreading
- Synthesis of RNA and protein resumes
- Cell confirms the number of chromosomes

M Phase (mitosis)
- AIM: divide the genome, then the cell

, - Mitosis
- Align and divide sister chromatids
- Divide the nucleus
- Divide the cytoplasm (Cytokinesis)

Cell cycle – key transition points
- Cell cycle checkpoints prevent progression until a
condition is met
- Transitions regulated by cyclins in complex with
cyclin dependent kinases
- Universally conserved
- Checkpoints make sure cells don’t go into mitosis
if they aren’t ready

Yeast as a model organism
- Unicellular; fast cell cycle
- Haploid (each gene in only one copy); easy genetic manipulations
- Were used to discover cdc genes (cellular division cycle)




- Has a characteristic cell shape change throughout the cell cycle, so
easy to identify each stage
- Easy to add GFP to it

Role for chemical signals in cell cycle regulation
- Fuse M phase nucleus with G1 (interphase)
cell
- Cell in G1 immediately enters mitosis
- Chromosomes not replicated
- Spindle forms normally with condensed,
but unduplicated chromosomes
- Nuclear envelope breaks down

Cdk-cyclins: controllers of cell cycle
- Cdk is inactive until bound to Cyclin
- Various combinations of Cdk (1-6) and Cyclins
(A-E) in different phases of cell cycle