Mechanisms of Disease I - Cell Growth and Differentiation Flashcards

1
Q

Define cell growth and differentiation

A

Cell growth - bigger organism, more cells

Differentiation - cells become complex, an end to growth

Cell growth precedes differentiation, but with some overlap

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2
Q

What are the 2 forms of cell growth

A

Hypertrophy - Bigger cells

Hyperplasia - more cells

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3
Q

Define Hypertrophy

A

Hypertrophy is simply cells growing bigger

More proteins, more membrane

Elevated protein synthesis is a big driver of increased cell size

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4
Q

Define Hyperplasia

A

More cells, caused by cell division or proliferation

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5
Q

Define differentiation

A

Where a cell exits the cell cycle and the cell is programmed to express type-specific genes.

Cell morphology and function changes

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6
Q

What is common between growth and differentiation

A

Cell growth and differentiation are governed by the integration of multiple signals: intra- and extracellular signals

Signals converge on the promoters of key genes
Promoters act as “co-incidence detectors”
Express gene YES/NO? How much?

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7
Q

What are the three types of ligand signalling methods

A
  • Paracrine: produced locally to stimulate proliferation of a different cell type that has the appropriate cell surface receptor
  • Autocrine: produced by a cell that also expresses the appropriate cell surface receptor
  • Endocrine: like conventional hormones, released systemically for distant effects
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8
Q

What are the extracellular signals and what do they do ?

A

Stimulate proliferation and promote survival
Mitogens
e.g. Growth factors and interleukins (EGF, FGF, NGF, PDGF, IGF1, IL2, IL4)

Induce differentiation and inhibit proliferation, e.g. TGFb
Can do either, e.g. Wnt ligands

Induce apoptosis, e.g. TNFα and other members of the TNF family

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9
Q

Describe the growth factor signalling pathway in the cell

A

1) Growth factor binds receptor
2) Signal transducers activate kinase cascade
3) Transcription factors are activated in the nucleus
4) mRNA is translated into proteins
5) Proteins made can either return to there nucleus, remain in the cytoplasm or go the the cell membrane

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10
Q

Describe the phases of the cell cycle

A

G0 - Quiescent cells, Can either go onto becoming differentiated or rejoin the cell cycle

G1 - Cells grows in size as most macromolecules are synthesised

S - DNA replication occurs

G2 - The cell grows more

Mitosis - The cells divides into 2 daughter cells

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11
Q

How can we measure DNA content of a cell

A

Fluorescent flo cytometry

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12
Q

Describe how a flow cytometry table would look for Low rate of division

A

60% of cells would be in G1 where they have the lowest amount of DNA

20% of cells would be in S phase where there is slowly and increasing amount of DNA

20% would be in G2 where all the cells would have undergone DNA replication

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13
Q

Describe how a flow cytometry table would look for High rate of division

A

40% of cells would be in G1 where they have the lowest amount of DNA

40% of cells would be in S phase where there is slowly and increasing amount of DNA

20% would be in G2 where all the cells would have undergone DNA replication

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14
Q

In fluorescence microscopy what does each stain colour show

A

Blue= DNA
Red = γ-tubulin
Green = CHEK2

Yellow = centrioles
(γ-tubulin and CHEK2 colocalised)

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15
Q

Outline the checkpoints present in the cell cycle and what it checks for

A

1st check near end of G1, Check for DNA damage, cell size and metabolite/nutrient stores

2nd check at end of G2, Check for DNA damage and if DNA is completely replicated

3rd check during mitosis, Check for if chromosomes are aligned on spindle

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16
Q

Explain how Cyclin-dependant Kinases operate

A

When enough cyclin is present in the cell it binds and activates cyclin dependant kinases, which phosphorylates specific substrates

Cyclin is produced by the induction of Growth Factors

17
Q

How is Cyclin-CDK activity regulated

A

Cycles of synthesis (gene expression) and destruction (by proteasome)

Post translational modification by phosphorylation

Dephosphorylation

Binding of cyclin-dependent kinase inhibitors (CDKIs)

18
Q

Explain how Retinoblastoma is a key substrate for S-Phase initiation

A

Unphosphorylated RB binds E2F transcription factor preventing its stimulation of S-phase protein expression

Cyclin D-CDK4 and E-CDK2 phosphate RB and releases E2F

Released E2F stimulates the expression of more Cyclin E and
S-phase proteins

19
Q

What happens when there’s DNA damage during the cell cycle

A

1) Stop the cycle
(cyclin dependent kinase inhibitors, CHEK2 etc.)

2)Attempt DNA repair
(nucleotide or base excision enzymes, mismatch repair etc.)

3) if repair impossible
Programmed Cell Death (BCL2 family, caspases)

20
Q

What is the role of Tumour protein 53

A

TP53 is normally destroyed by proteasome in a normal cells,
When there is DNA damage kinase activation phosphorylates TP53 so it isn’t destroyed.

phosphorylated TP53 can cause:
1) DNA Repair
2) Apoptosis
3) Expression of CDKI, cell cycle arrest

21
Q

What would the effects be of the loss of TP53

A

TP53 loss-of-function mutations are amongst the most frequent in cancer

  • Prevent cell cycle arrest
  • Prevent apoptosis
  • Prevent DNA repair
22
Q

How does S-phase chemotherapy drugs work

A

Objective: stop proliferation, induce apoptosis

S-phase drugs cause DNA damage, e.g.
5-fluorouracil (prevents synthesis of thymidine)

Cisplatin (binds to DNA causing damage and blocking repair)

23
Q

How does M-phase chemotherapy drugs work

A

M-Phase drugs target the mitotic spindle
Vinca alkaloids:
stabilize free tubulin
prevent microtubule polymerization
arrest cells in mitosis

Paclitaxel (Taxol):
stabilizes microtubules
preventing de-polymerization
arrests cell in mitosis