Cell cycle Flashcards
What is cell proliferation for?
Normal development
Homeostasis
Replace dead/injured cells
What are the 3 classes of proliferative capacity?
- Labile cells - continuously divide
- Stable cells - infrequent divisions
- Permanent cells - never divide in adult life
What is the difference between pluripotent & totipotent stem cells?
Pluripotent - ability to self-renew & produce multiple types of specialised cells (adult stem cells)
Totipotent - give rise to all types of cells (embryonic SC)
What stimulates cell proliferation?
Growth factors
Describe the cell cycle
- G0 - cell resting/quiescent
- G1 - prepares DNA for synthesis
- S - DNA replicates
G2 - nuclear envelope broken down, mitotic spindle assembled & chromosomes aligned
What are the 5 steps in mitosis?
- Prophase - chromosomes shorten
- Metaphase - chromosomes line up along equator
- Anaphase - spindle fibres shorten & pull chromosomes apart
- Telophase - chromosomes unravel & nuclear envlope reform
- Cytokinesis - division of cytoplasm
What are the positive & negative controls of the cell cycle?
Positive - signals from outside cell (e.g. GF)
Negative - cyclin kinase inhibitors, checkpoints
Where are the checkpoints in the cell cycle and what do they do?
G1-S - monitors integrity of DNA before synthesis
G2-M - monitors integrity of replicated DNA
What may happen if a checkpoint is activated?
- Activate DNA repair mechanism & resume replication
- Apoptosis
- Permanent senescence
Which checkpoint does P53 act?
At the G1-S checkpoint.
Senses DNA damage & binds to it cause gene expression to -
- Induce p21 (CKD inhibitor) - stop cell cycle
- Trigger apoptosis
- Activate DNA repair
What is hyperplasia?
Increased cell number.
Cell must be labile or stable
What is hypertrophy?
Increased cell size.
Occurs in any cells.
Common when permanent cells have increased demands.
More cellular structural proteins produced.
What is atrophy?
Decreased cell size.
Loss of cell substance due to autophagy of organelles
What is metaplasia?
Reversible change from one adult cell type to another.
Adaptive response.
Usually involves epithelium
What is dysplasia?
Increased cell growth
