Cellular growth regulation Flashcards
What is the difference between hyperplasia and hypertrophy?
HyperPlasia = increase in cell numbers
Hint: P = Plenty
Hypertrophy = increase in cell size
What is apoptosis?
A coordinated programme of cell dismantling followed by phagocytosis
Give examples of where apoptosis can occur during normal development
- Separation of the digits
- Involution
- Immune system development
- Nervous system development
what is involution?
For example it is when the uterus returning to normal size post pregnancy
Apart from during normal development, what else can trigger apoptosis to occur?
Can occur in response to DNA damage and viral infection
What 3 roles do GF, Cytokines and IL play? Give specific examples
- Stimulate proliferation and maintain survival (mitogens)
- Stimulate differentiation and inhibit proliferation (TGF-B)
- Induce apoptosis (TNF-A)
Give examples of mitogens
- EGF
- FGF
- IL2 & IL4
- NGF
- PDGF (platelet derived growth factor)
- IGF1 (insulin like growth factor)
What are the proteins that stimulate proliferation called?
Mitogens
These are required for the survival of the cells
Function of TGF-B (transforming growth factor beta)
- Stimulates differentiation
2. Inhibits proliferation
Function of TNF-A (tumour necrosis factor alpha)
Induces apoptosis
Name and describe the 3 methods of signalling
Paracrine:
Produced locally to stimulate a DIFFERENT CELL TYPE with the appropriate cell surface receptor
Autocrine:
Produced by a cell that acts on the SAME CELL TYPE with the appropriate cell surface receptor
Endocrine:
Released to act on distant cells
Outline the stages of the cell cycle
- The cell cycle consists of four stages: G1, S, G2, and M.
- G1 and G2 are ‘gap’ phases in which the cell grows and prepares to divide.
- S in the synthesis phase in which the chromosomes (DNA) are copied (replicated).
- M is the mitotic phase in which the cell physically divides into two daughter cells.
- Most cells are NOT actively dividing. These cells are in a resting state (G0)
What happens during M phase?
Mitosis in normal cells produces TWO cells with identical genetic content.
The daughter cells can:
• Re-enter the cell cycle
• Withdraws from the cell cycle (arrests). This cell is in the G0 phase of the cell cycle and is called the Quiescent cells. These cells can then take 2 different paths:
1. These cells can re-enter the cell cycle and start dividing if stimulated by mitogen (growth factor)
OR
2. Receive TGF-B which will induce differentiation of the cells. These cells can then renew the cells removed by cell shedding/apoptosis .
2N = how many chromosomes? 4N = how many chromosomes?
2N = 23 chromosomes 4N = 46 chromosomes
What are the 2 fates of a daughter cell arrested in mitosis (G0)?
- These cells can re-enter the cell cycle and start dividing if stimulated by mitogen (growth factor)
OR - Receive TGF-B which will induce differentiation of the cells. These cells can then be used to renew the cells removed by cell shedding/apoptosis.
What is a fluorescent DNA stain and how is it used?
Use a fluorescent DNA stain to treat the cells. This will bind to DNA. This can then be used to measure the amount of DNA present.
FLUORESCENT DNA STAIN
During a LOW rate of cell division, what phase of the cell cycle would the majority of the cells be found in?
majority found in G1 (60%)
FLUORESCENT DNA STAIN
During a HIGH rate of cell division, what phase of the cell cycle would the majority of the cells be found in?
(in comparison to a low rate of cell division, what would the shift in % be?)
COMPARED TO LOW RATE OF CELL DIVISION (where 60% of cells were found in G1) there would be:
less cells found in G1 phase
AND
more cells found in S/G2/M phase
this is because during high cell division, more of the cells will be progressing through the cell cycle
As a recap, go through DNA replication
1) DNA is replicated semi conservatively (daughter cells inherit one parental and one new strand).
2) New DNA is synthesized in the 5’ to 3’ direction from deoxynucleotide triphosphate precursors at a replication fork by a multienzyme complex (a replication machine).
3) Fidelity is determined by base pairing (A=T, G≡C) and presence of a proof reading enzyme in DNA polymerase.
4) Synthesis of the new DNA strand uses an RNA primer and occurs continuously on the leading strand and discontinuously on the trailing strand (giving rise to Okazaki fragments, which are ligated together after removal of the RNA primer).
Describe the 4 stages of mitosis in terms of what changes can be seen within the cell under a microscope
1) PROPHASE:
- Nucleus becomes less definite
- Microtubular spindle apparatus assembles
- Centrioles (yellow) migrate to poles
PROMETAPHASE:
- Nuclear membrane breaks down
- Kinetochores attach to spindle in nuclear region
2) METAPHASE:
- Chromosomes (blue) align in equatorial plane
3) ANAPHASE:
- Chromatids separate and migrate to opposite poles
4) TELOPHASE:
- Daughter nuclei form
Another phase that is considered is CYTOKINESIS:
- Division of cytoplasm
- Chromosomes decondense
Name 2 drugs that can act during the S phase of mitosis and describe what it does
5-fluorouracil (an analogue of thymidine BLOCKS thymidylate synthase activity)
No thymidine = no DNA replication = arrests mitosis in S phase
Bromodeoxyuridine aka BrdU (an analogue that can be incorporated into DNA, it is detected by antibodies to identify the cells that have passed through the S phase)
what is 5-fluorouracil
(an analogue of thymidine BLOCKS thymidylate synthase activity)
No thymidine = no DNA replication = arrests mitosis in S phase
what is Bromodeoxyuridine aka BrdU
(an analogue that can be incorporated into DNA, it is detected by antibodies to identify the cells that have passed through the S phase)
What is tamoxifen and its role in breast cancer?
Oestrogen is required for the breast cancer cells to grow. Tamoxifen is an antagonist of oestrogen. Cells can be treated with tamoxifen to prevent growth of breast cancer cells. You can check if the growth of the cells has stopped using BrdU which will bind to any breast cancer cells that have progressed through the S phase. After tamoxifen treatment the amount of BrdU detected should decrease.
Tamoxifen = less BrdU detected = indicates less breast cancer cells progressing through S phase
Name 2 drugs that can act during the M phase of mitosis and describe what it does
Colchicine
• Stabilises free tubulin = preventing microtubule polymerisation = arrests cells in mitosis therefore they cannot divide
• This can be used in karyotype analysis
Vinca alkaloids (similar action to colchicine) Paclitaxel (taxol) • Stabilises microtubules • Prevents destabilisation This means the cells cannot separate
Name 2 drugs that can act during the M phase of mitosis and describe what it does
Colchicine
• Stabilises free tubulin = preventing microtubule polymerisation = arrests cells in mitosis therefore they cannot divide
• This can be used in karyotype analysis
Vinca alkaloids (similar action to colchicine)
Paclitaxel (taxol)
• Stabilises microtubules
• Prevents destabilisation
This means the cells cannot separate
what is the role of the drug colchicine during the M phase
• Stabilises free tubulin = preventing microtubule polymerisation = arrests cells in mitosis therefore they cannot divide
This can be used in karyotype analysis
what is the role of vinca alkaloids during the M phase
similar action to colchicine
arrests cells in mitosis therefore they cannot divide
Name 4 drugs used in the treatment of cancer
- 5-flurouracil
- Paclitaxel
- Vinca alkaloids
- Tamoxifen
These all act to prevent cell division/growth of tumours
G1 and G2 checkpoints can detect DNA damage. If DNA damage is detected, what 2 things can happen?
Triggers cell cycle arrest to try and attempt to repair the DNA and IF repaired it can re-enter the cell cycle
OR
IF DNA repair CANNOT occur/is impossible then apoptosis occurs
G1 and G2 checkpoints can detect DNA damage. This then triggers cell cycle arrest. What 2 things can be used to trigger cell cycle arrest?
Cyclin dependent kinase inhibitors
CHEK2
G1 and G2 checkpoints can detect DNA damage. This then triggers cell cycle arrest to attempt DNA repair. What is used to attempt repair of the DNA?
nucleotide or base excision enzymes
mismatch repair enzymes
G1 and G2 checkpoints can detect DNA damage. This then triggers cell cycle arrest to try to repair the DNA. However, if the DNA cannot be repaired, apoptosis is triggered. What is involved in the apoptosis of the damaged irreparable cells
BCL2 family
Caspases
What are the controls involved in the cell cycle checkpoints? What is involved in them and what are their roles?
Controls (involving specific protein kinases and phosphatases) ensure the strict alternation of mitosis and DNA replication
What are the 3 cell cycle checkpoints and what is the purpose of each of them?
1. G1 checkpoint checks for: • DNA damage • Cell size • Metabolites/nutrient store 2. G2 checkpoint checks for: • Complete DNA replication • No DNA damage 3. M checkpoint checks for: • Chromosomes aligned on the spindle
At what point in the cell cycle are the cells responsive to growth factors?
G1 phase is where the cells are responsive to growth factors
This is the main site of control for cell growth
What is progression through the cell cycle controlled by?
Cyclin-dependent kinase activity
