Cellular Growth Regulation Flashcards
What is the difference between hyperplasia and hypertrophy?
Hyperplasia= increase in cell NUMBER Hypertrophy= increase in cell SIZE
Give an example of cellular hypertrophy?
Exercising—>Bigger Heart–>Increase in cell size NOT number
The growth of a population of cells depends on the integration of what?
Intra and extracellular signals
What do intra and extracellular signals check? (4 examples)
1) Cellular Pathology
2) Growth
3) Inhibitory Factors
4) Cell Adhesion
What is one key difference between growth at cellular level and a population of cells in terms of hyperplasia and hypertrophy?
At growth at the cellular level (cell cycle) it is due to increase in size (hypertrophy) and cell division.
Growth of a population of the cells you have to distinguish between hyperplasia and hypertrophy.
List the cell cycle phases?
G1, S,G2,M
What is the progression of the cell cycle controlled by?
Three key checkpoints- restriction points
Define Apoptosis?
A coordinated program of cell dismantling ending in phagocytosis
Define Necrosis?
Is apoptosis similar to necrosis or not?
Necrosis is the death of most/all cells due to injury or poor blood supply. Apoptosis is distinct from necrosis
Necrosis occurs as a response to injury or blood loss.
What does apoptosis respond to?
DNA damage and viral infection
What are mitogens?
Proteins that stimulate proliferation
triggers mitosis , hence the name
What do growth factors, cytokines and interleukins do?
- Stimulate Proliferation
- Maintain Survival
- Stimulate Differentiation
- Inhibit Proliferation
- Induce Apoptosis
What is a growth factor that?
- Inhibits Proliferation
- Induces Apoptosis
- TGFbeta
- TNFalpha and other members of the TNF family
What are the three broad classes of growth factors, cytokines and interleukins
1) Paracrine
2) Autocrine
3) Endocrine
Briefly describe the differences between paracrine, autocrine and endocrine?
Paracrine= Stimulates proliferation of a diff cell type with correct receptor Autocrine = When a cell signals to itself Endocrine= Distant signals (hormones that act on distant target cells)
On a graph where you're measuring the log of cell number over days What effect would -GF addition -GF removal -Growth Inhibitor -Death signal -Protein running out
- Addition = cell number increasing
- Removal = Graph will plateau
- Inhibitor = Graph will plateau
- Death signal = Graph will decline
- Protein running out = Graph will plateau
Give an example of a growth factor and inhibitor
Growth factor = PDGF
Growth Inhibitor = TGFbeta
What occurs in the interphase of the cell cycle?
Cell GROWS in size
Make more cytoskeleton to grow
Macromolecules synthesised continuously
What occurs in the S phase of the cell cycle?
DNA Replication
Incorporate Thymidine
2n—>4n for G2 and M
What occurs in the G0 phase in the cell cycle?
Quiescent Cells - Cells that are not dividing but some can re-enter the cell cycle or some go through terminal differentiation
What occurs after terminal differentiation?
Cell shredding- APOPTOSIS
What is a fluorescence activated cell sorter analysis used for?
Used to check whether cells are growing and what stage they are in
Explain the steps in using a fluorescence activated cell sorter analysis
1) Take cells and label DNA with dye
2) Dye read by laser- laser indicates how intense DNA content is
3) Machine determines how fluorescent the nuclei of cells are in each phase
4) Cells not growing that fast = G1
5) Cells can be treated with GF’s to see effects
“DNA is replicated semi-conservatively”
What does this mean?
Daughter cells inherit one parental and one new strand
What direction in new DNA synthesised in?
5’ to 3’
How is new DNA synthesised?
From a deoxynucleotide triphosphate precursor at a replication fork by a multicomplex enzyme
What is Fidelity?
AND
How is it Determined?
Fidelity= how much of a exact copy something is
Determined by two things:
1)Base Pairing
2)Presence of proof reading enzyme in DNA Pol
Synthesis of the new DNA strand uses an RNA primer and occurs continuously on which strand?
Discontinuously on which strand?
Continuously on the LEADING STRAND
Discontinuously strand on the TRAILING STRAND
What does the trailing strand give rise to?
Okazaki fragments
RNA primer removed
Okazaki fragments ligated together
What are the 4 main stages of Mitosis?
1) Prophase
2) Metaphase
3)Anaphase
4)Telophase
and then its not a phase but cytokinesis
What occurs during Prophase?
- Nucleus becomes less definite
- Micro-tubular spindle apparatus assembles
- Centrioles migrate to poles
What occurs between prophase and metaphase but isn’t a phase itself?
Prometaphase
- Nuclear membrane breaks down
- Kinetochores attach to spindle in nuclear region
What occurs in metaphase?
-Chromosomes align in the equatorial plane
What occurs in Anaphase?
-Chromatids separate and migrate to opposite poles
What occurs in Telophase?
Daughter nuclei form
What happens after telophase?
Cytokinesis
- Division of cytoplasm
- Chromosomes decondense
What are 2 drugs that act in the S phase ( S phase active)?
5-Fluorouracil
Bromodeoxyuridine
What does 5-Fluorouracil do?
An analogue of thymidine
Blocks thymidylate synthesis
What does Bromodeoxyuridine
Analogue of thymidine
Can be incorporated into DNA –> Detected by antibodies –>Identify cells that have passed through the S-Phase
What are 3 drugs that act in the M Phase (M Phase Active)?
1) Colchicine
2) Vinca Alkaloids
3) Paclitaxel
What does Colchicine and Vinca Alkaloids do?
-Stabilises free tubulin
-Prevents microtubule polymerisation
-Arresting cells in mitosis
Used in Karyotype Analysis
What does Paclitaxel/Taxol do?
- Stabilises Microtubules
- Prevents de-polymerization
What are 4 drugs you can use in the treatment of cancer?
5-Flurouracil
Paclitaxel
Vinca Alkaloids
Tamoxifen
What are cell cycle checkpoints?
Controls (involving specific protein kinases and phosphatases) ensure the strict alternation of mitosis and DNA replication
What is the cell cycle checkpoints before?
-S Phase
-M Phase
And during metaphase
Before S phase = DNA not damaged, Cell Size and Metabolite
Before M Phase = DNA completely replicated and DNA not damaged
During Metaphase = Chromosomes alligned on spindle
Which phase is the only phase in which cells can respond to extracellular molecules eg mitogens
G1
Explain the regulation of cyclin-CDK Activity?
Balance between Cyclical Synthesis (Gene expression) and Destruction (By Proteasome)
Post translational modification by phosphorylation - depending on the modifications site it could result in activation, inhibition or destruction.
What do active Cyclin-CDK complex do?
Phosphorylate specific substrates
How many genes in the CDK subunit and Cyclin regulatory subunit?
CDK = 10 Genes Cyclin = > 20 Genes
Match up -CDK -Cyclin TO: -Regulatory -Catalytic
CDK - Catalytic Subunit (10 genees)
Cyclin - Regulatory Subunit (<20 genes)
How do you dephosphorylate substrates ?
Binding of CDK inhibitors
Pick one of the following the best describes the action of the retinoblastoma protein:
- Tumour Activation
- Tumour Suppressing
- Transcription Factor
Tumor Suppressing
What does tumour suppressor mean in terms of retinoblastoma?
It inhibits the progression of the cell cycle
It acts in the G0 and G1 phase to decide if a cell is ready to move to the S phase
If the DNA is damaged (ie tumour) retinoblastoma would inhibit the cell from progressing in the cell cycle and therefore suppresses the tumour
In the absence of D-CDK’s , how does Retinoblastoma act?
In their absence, RB wont be phosphorylated which means it can bind to the transcription factor E2F, this inactivates the TF so that the cell cycle progression is inhibited
In the presence of D-CDK’s, how does retinoblastoma act?
As D-CDK’s are KINASES, they phosphorylate, so they phosphorylate RB and it can no longer bind to E2F.
E2F is released from the complex , makes more cyclin E (needed for the CDK’s to work) and S-Phase proteins. As E2F is a TF- it makes components needed for cell growth
What types of the cyclin are needed for CDK4 and CDK2 (these are the CDK’s used to phosphorylate RB)?
Cyclin D- CDK4
Cyclin E- CDK2
Remember this because the transcription factor is E2f, so cyclin E must match with CDK2
What two families of CDK inhibitors are there?
1) CIP/KIP , now called CDKN1
2) INK4 , now called CDKN2
This question relates to CDKN1 only
- What is it weakly stimulated by?
- What is it strongly stimulated by?
- What CDK-cylin complexes does it inhibit?
- Which stage in the cell cycle is it sequestered and how?
- TGFbeta
- DNA Damage
- All other CDK-Cyclin complexes
- Gradually sequestered by G1 CDK’s so later CDK’s are activated
This question relates to CDKN2 only?
- What is it stimulated by?
- Which CDK-Cyclin complexes does it inhibit
- TFGbeta
2. Specifically inhibit G1 CDK’s
Explain how an increase in mitogens results in an increase in cyclin expression?
- Mitogens induce GF to bind to GFr
- This results in signal transducers being activated
- There is a kinase cascade
- (Nucleus) Transcription begin begins, codes for proteins
What activates :
- G1 CDK’s
- Late CDK’s
G1 CDK’s are activated in response to environmental signals
Late CDK’s are activated in responses to preceding kinase activities
What dephosphorylates hyperphosphorylated RB?
Protein phosphatase 1
Out of G1 CDK’s and late CDK’s which ones hyperphosphorylate and hypophosphorylate ?
G1 CDK’s HYPOphosphorylate
Late CDK’s HYPERphosphorylate
Explain the sequence of events triggered by growth factors that help the cell get through S-phase and mitosis
- Growth factor signalling activates early gene expression
- Early gene products stimulate delayed gene expression (includes Cyclin D, CDK2/4 and E2F)
- E2F sequestered by binding to unphosphorylated RB
- G1 cyclin-CDK complexes hypophosphorylate RB and then G1/S cyclin-CDK complexes
hyperphosphorylate RB releasing E2F - E2F stimulates expression of more Cyclin E and S-phase proteins (e.g. DNA polymerase, thymidine
kinase, Proliferating Cell Nuclear Antigen etc.)
 - S-phase cyclin-CDK and G2/M cyclin-CDK complexes build up in inactive forms. These switches are activated by post-translational modification or removal of inhibitors, driving the cell through S-phase and mitosis.
This question is about DNA Damage:
- How is it detected?
- What does it trigger?
- If you attempt to repair DNA damage , and it works what will happen? What will happen if you cant repair it?
- Detected at checkpoints
- Triggers Apoptosis
- If repaired = re-enters cell cycle
- If not repaired = Apoptosis
Explain how TP53 responds to DNA Damage?
- There is a mutation in DNA
- This damage is detected by kinases (ATM , ATR)
- Kinases activate checkpoint 2
4.P53 is phosphorylated so cant be degraded
5.P53 becomes a stabilised protein - bind to promoters of TFs - Express genes required for DNA repair
(IF cant repair - APOPTOSIS)
