L2: Cell growth & Differentiation

Question 1

What are the types of diseases related to cell growth and differentiation?

Answer 1

→Developmental conditions
Can be related to cell growth or differentiation (or both)
E.g. Neural tube defects like spina bifida

→Neoplasia (and metaplasia)
E.g. cancer, tumours

→Others, e.g. cardiac hypertrophy

Question 2

What is the most common type of cell growth? Give an example

Answer 2

→hyperplasia

Question 3

What drives hypertrophy? Give an example

Answer 3

→More proteins, more membrane etc etc.

→Elevated protein synthesis is a big driver of increased cell size

Question 4

What are post-mitotic cells?

Answer 4

→Exit from the cell cycle

→differentiated cells

Question 5

What are the three types pf extracellular signals?

Answer 5

→paracrine
→autocrine
→endocrine

Question 6

What are mitogens?

Answer 6

→Stimulate proliferation and promote survival

Question 7

Give examples of mitogens

Answer 7

→Growth factors and interleukins (EGF, FGF, NGF, PDGF, IGF1, IL2, IL4

Question 8

What can extracellular signals do?

Answer 8

→Stimulate proliferation and promote survival
→Induce differentiation and inhibit proliferation, e.g. TGF
→Can do either, e.g. Wnt ligands
→Induce apoptosis, e.g. TNFα and other members of the TNF family

Question 9

What are the phases of the cell cycle?

Answer 9

mitosis
→G1
→synthesis
→G2

Question 10

What allows FACS analysis to work?

Answer 10

DNA content ie ploidy

2N or 4N

Question 11

Compare FACs analysis in normal and highly proliferative population

Answer 11

→in a highly proliferative population, G1 phase has a lower peak
→increased S-phase
→similar G2 phase because it is time limited

Question 12

What is fluorescence microscopy used for?

Answer 12

→ visualising stages of the cell cycle

Question 13

What do the colours of fluorescence microscopy represent?

Answer 13

Blue= DNA
Red = γ-tubulin Green = CHEK2

Yellow = centrioles
(γ-tubulin and CHEK2 colocalised)

Question 14

What are the four main phases of mitosis?

Answer 14

→prophase
→metaphase
→anaphase
→telophase

Question 15

What happens in prophase?

Answer 15

→Nucleus becomes less definite
→Microtubular spindle apparatus assembles
→Centrioles migrate to poles

Question 16

What happens in prometaphase?

Answer 16

→Nuclear membrane breaks down

→Kinetochores attach to spindle in nuclear region

Question 17

What happens in metaphase?

Answer 17

Chromosomes align in equatorial plane

Question 18

What happens in anaphase?

Answer 18

Chromatids separate and migrate to opposite poles

Question 19

What happens in telophase?

Answer 19

Daughter nuclei form

Question 20

What happens in cytokinesis?

Answer 20

→Division of cytoplasm

→Chromosomes decondense

Question 21

What are the cell cycle checkpoints and what do they check for?

Answer 21

→Restriction point: 
DNA not damaged, Cell size,
metabolite/nutrient stores
Happens just before S-phase
→DNA completely replicated,
DNA not damaged
Happens at M
→Chromosomes aligned on spindle
Happens at mid-M phase

Question 22

How many genes code for CDKs?

Answer 22

→10 genes

Question 23

What do active cyclin-CDK complex do?

Answer 23

→Phosphorylates specific substrates

Question 24

How many genes encode cyclins?

Answer 24

→20 genes

Question 25

What induces cyclins(regulatory subunits)?

Answer 25

→expression of growth factors

Question 26

What is retinoblastoma protein?

Answer 26

→a key substrate of G1 and G1/S cyclin-dependent kinases

Question 27

Describe how RB works

Answer 27

→Unphosphorylated RB binds E2F transcription factor preventing its stimulation of S-phase protein expression
→CD-CDK4 and CE-CDK2 phosphorylate RB
→ E2F is released
→Released E2F stimulates expression of more Cyclin E and S-phase proteins e.g. DNA polymerase, thymidine kinase, PCNA etc.
DNA replication starts.

Question 28

What are hyperphosphorylated RB dephosphorylated by?

Answer 28

→protein phosphatase 1

Question 29

Describe the sequence of events triggered by growth factors

Answer 29

→Growth factor signalling activates early gene expression (transcription factors – FOS, JUN, MYC)

Early gene products stimulate delayed gene expression (includes Cyclin D, CDK2/4 and E2F transcription factors)

E2F sequestered by binding to unphosphorylated retinoblastoma protein (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.

Question 30

What can happen if there is DNA damage?

Answer 30

→Stop the cycle
(cyclin dependent kinase inhibitors, CHEK2 etc.)
→Attempt DNA repair
(nucleotide or base excision enzymes, mismatch repair etc.)
→if repair impossible
Programmed Cell Death (BCL2 family, caspases)

Question 31

What can TP53 loss of function lead to?

Answer 31

→Prevent cell cycle arrest
→Prevent apoptosis
→Prevent DNA repair

Question 32

What can more mutations lead to?

Answer 32

= more heterogeneity
= more adaptation
= cancer progression

Question 33

What are the objectives of traditional chemotherapeutic drugs?

Answer 33

stop proliferation, induce apoptosis

Question 34

Give examples of S-phase drugs and how they work

Answer 34

→5-fluorouracil (prevents synthesis of thymidine)

→Cisplatin (binds to DNA causing damage and blocking repair)

Question 35

How do M-phase drugs work?

Answer 35

Vinca alkaloids
→stabilize free tubulin
→prevent microtubule polymerization- no
→mitotic spindle arrest cells in mitosis

Question 36

how does Paclitaxel work?

Answer 36

→stabilizes microtubules
→preventing de-polymerization
→arrests cell in mitosis

Question 37

What is colchicine?

Answer 37

→similar mode of action to vinca alkaloids

→ is used for immune-suppression