7. Cellular Adaptations Flashcards
(53 cards)
How is cell proliferation controlled
—-> Largely by chemical signals from the microenvironment which either stimulate or inhibit cell proliferation by binding to receptors
How do cells survive
• Cell needs prosurvive signals
○ Survive – resist apoptosis
○ An no division
○ Always need the pro survival signals to maintain cell life
Cell death
Apoptosis
Stages of cell cycle
G1
S
G2
M – mitosis
Mitosis
Stages
- Prophase
- Metaphase
- Anaphase
- Telophase
G0 phase
• Terminal differentiation
• Permamnt exit from cell cycle
• Where quiscent cells are that have stopped dividing
○ Some cells can move in and out of G0 phase
Increased growth occurs by:
- Shortening the cell cycle = go through cycle faster
* Conversion of quiescent cells to proliferating cells by making them enter the cell cycle.
3 Cell cycle checkpoints
• G1 – detect nutrients for ccell cycle like growth factos
G2 – check forcorrectly replicated DNA
Metaphase to anaphase – check spindle is connected to chromosome
Restriction (R) checkpoint
Majority of cells that pass R point will complete cell cycle - point of no return
This checkpoint is most commonly altered in cancer cells
• Mutate genes to inactivate checkpoint and go through without control
Chrcpoint activation delays cell cycle, triggers DNA repair, apoptosis via p53
CDK activation
- Cyclin and CDK bind together
- When they come togeter they are partially active then fully active
- Once active it can phosphorylate other targets
Control CDK cyclin interactions
- The regulation of Cdk activity by phosphorylation
* The inhibition of a cyclin–Cdk complex by a CKI – inhibitor proteins bind to and inactivate proteins
Leonard Hayflick - Hayflick numbers/limits (1961)
- Limit to how much the cells can divide
- Nnumber of cell divisions human cell can go through
- Humans = 40-60 divisions normally until it stops
Why does cell division eventually stop
• As with each division you lose some part of the telomeres
• When the telomeres become too short = cells become senscent
○ Somatic cells don’t have enough telomerase - loose ability to express telomerase to maintain telomeres ends
➢ How to cancer cells survive?
- Cell override the stopping and can continue to divide
- Cancer cells use and reexpress telomerase which maintains the telomere sites
- Normlly telomerase is expressed at low levels in somatic cells
Proliferation:
• increase in numbers of cells
Growth:
• increase in size of the cell ○ Multiplicative growth ○ Ausectic growth ○ Accretionary growth ○ Combined pattern of growth
Differentiation:
• acquiring a specific morphology and function
Factors impacting size of a cell population
Depends on
• rate of cell proliferation
• cell differentiation
• cell death by apoptosis
• Increased numbers are seen with increased proliferation or decreased cell death
Regeneration:
• the ability to replace cells or tissues, destroyed by injury or disease (identical functionality)
3 types of cells
Labile
Stable
Permanent
Table cells
•Labile cells: high regenerative ability and turnover (e.g. intestinal epithelium)
Stable cells
• Stable cells: good regenerative ability and low turnover (e.g. hepatocytes) - can return to G1 and start regenerating
Permanent cells
• Permanent cells: no regenerative ability (e.g. neurones, cardiac, skeletal muscle cells)
Hyperplasia
• Hyperplasia – cells increase in number above normal
