L2 - Mechanisms of Disease: Cell growth + differentiation

Question 1

What is cell growth?

Answer 1

division of cells by mitosis to produce a bigger organism

Question 2

What is cell differentiation?

Answer 2

the transition of a cell from one type to another to produce a complex, multi-function organism.
Exit from the cell cycle are called post-mitotic.
Begins to express cell-specific genes, and therefore its morphology and function changes.

Question 3

Describe Hypertrophy in terms of cell growth?

Answer 3

When cell become bigger:
cells make more macro-molecules (proteins, more membrane etc)
Caused by elevated protein synthesis
The heart is a good example

Question 4

Describe Hyperplasia in terms of cell growth?

Answer 4

When number of cells increases due to proliferation

Caused by the cell cycle

Question 5

What signals govern cell growth and differentiation and give examples of each?

Answer 5

Intracellular signals - checks on cellular physiology.

Extracellular signals - growth factors and cell adhesion

Question 6

Where do intracellular and extracellular signals integrate/converge?

Answer 6

on the promoters of key genes

Question 7

Describe extracellular signalling including the 3 types?

Answer 7

Ligand binds to a receptor and causes intracellular cascade.

3 classes of signalling: paracrine, autocrine, and endocrine

Question 8

Describe the role of extracellular signalling in cell growth and differentiation?

Answer 8

They are proteins that:

• stimulate proliferation and promote survival (growth factors and interleukins)
• induce differentiation and inhibit proliferation
• can do both (Wnt ligands)
• induce apoptosis (TNF family)

Question 9

What are the phases of the cell cycle?

Answer 9

Mitosis

Interphase: G1, S, G2

Question 10

What happens during Interphase of the cell cycle?

Answer 10

Cells grow larger in size and essential macromolecules are synthesised.
In S phase - the DNA is replicated.

Question 11

What are quiescent cells and what happens to them?

Answer 11

They are cells that leave the mitotic phase and enter the G0 phase. They either are stagnant in this stage until they rejoin the cell cycle in G1.
Or they begin the process of differentiation - and become terminally differentiated (post-mitotic).
May go onto cell death - apoptosis.

Question 12

How does the amount of DNA in the cell change throughout cell cycle?

Answer 12

G1 - 2N ploidy

G2 - Tetraploidy - 4N

Question 13

What is FACS and what is it used for?

Answer 13

Flourescence activated cell sorting.
Analyses the DNA content of cells in a population.
DNA stain is applied and FACS can measure the DNA content of every cell.

Question 14

How is fluorescence microscopy used to detect DNA?

Answer 14

Blue shows DNA
Red shows gamma tubulin
Green shows CHEK2
Yellow shows that Red and green are in the same place: centrioles.
Throughout the cell cycle the colour intensity and amount change and DNA can be measured.

Question 15

What do the cell cycle checkpoints involve and what are their roles?

Answer 15

Specific protein kinases and phosphatases.
Kinases add phosphate groups and phosphatases remove the phosphates.
They ensure that cells have duplicated correctly before entering mitosis and that cells have proliferated correctly before entering S phase.

Question 16

What is the purpose of the restriction point in the cell cycle and where is it located?

Answer 16

Located at the end of G1 phase.
Ensures that there is no DNA damage/errors in the DNA which would be copied in the S phase.
Also checks the nutrient/metabolite stores and the cell size.

Question 17

What is the purpose the G2 checkpoint?

Answer 17

Located at the end of G2

Ensures that the DNA has replicated correctly and is ready for mitosis.

Question 18

What is the purpose of the metaphase checkpoint?

Answer 18

Checks that the chromosomes have aligned on the spindle correctly

Question 19

What are CDKs and how many do we have?

Answer 19

Cyclin-dependant kinases - important kinases involved in regulating the cell cycle.
10 genes encode for CDK catalytic subunit
More than 20 genes encode for cyclin - the regulatory subunit

Question 20

What do growth factors induce the expression of and how does this help the cell cycle?

Answer 20

induce expression of cyclin genes, which allows it to forma complex with CDK. Active Cyclin-CDK phosphorylates substrates, which alows for progression of the cell cycle.

Question 21

How is Cyclin-CDK activity regulated?

Answer 21

cyclin proteins have a high rate of turnover. Continuously synthesised and destroyed.
Post translational modification of cyclins can result in activation, inhibition or destruction of kinase activity.
CDKIs also bind to cyclin complexes and inhibit them.

Question 22

Describe the events that occur if damage is detected in the DNA?

Answer 22

1) The cycle is stopped (CDK Inhibitors, CHEK2)
2) Attempt to repair the DNA damage (nucleotide or base excision, mismatch repair)
3) If repair is impossible - the cell enters apoptosis (capsases)

Question 23

Explain the role of TP53?

Answer 23

Tumor suppressor protein 53.
Made by the cell and destroyed by the proteosome.
However when a mutagen binds to DNA and causes damage to the DNA, it activated kinases that convert TP53 TO PHOSPHORYLATED TP53, which cannot be destroyed by the proteosome.
- Expresses CKIs which cause cell cycle arrest.
- Activation of DNA repair
- Activates cell death

Question 24

What are the effects of TP53 losing its function?

Answer 24

CANCER

• nothing to prevent cell cycle arrest - so faster growth of cells
• nothing to induce apoptosis - cells do not die
• prevents DNA repair - more mutations, more adaptation and cancer progression.

Question 25

What are the purpose of chemotherapeutic drugs?

Answer 25

They act on the cell cycle:

stop proliferation and induce apoptosis.

Question 26

What to S-phase drugs do in terms of chemotherapeutics and give examples?

Answer 26

They cause DNA damage:

• 5 flourouracil (prevents the synthesis of thymidine)
• Cisplatin (binds to DNA and causes damage and blocks repair)

Question 27

What to M-phase drugs do in terms of chemotherapeutics and give examples?

Answer 27

They target the mitotic spindle
- Vinca alkaloids (stabilises free tubulin which prevents polymerisation of tubulins to make microtubules - as a result a mitotic spindle cannot be formed. Arrests cells in mitosis)

• Paclitaxel (taxol)
  (Stabilises microtubules, prevents depolymerisation and arrests cells in mitosis)