Cellular growth regulation

Question 1

What does growth of a population of cells distinguish

Answer 1

Between increase in cell numbers (hyperplasia) and increase in cell size (hypertrophy)

Question 2

What does growth of a population of cells depend on

Answer 2

Depends on integration of intra- and extracellular signals

(checks on cellular
physiology, growth and inhibitory factors, cell adhesion etc.)

Question 3

What is cell growth

Answer 3

Increase in size (sometimes refers to growth only) + cell division

Question 4

What is apoptosis, when does it occur and what is it in response to

Answer 4

A coordinated program of cell dismantling ending in phagocytosis

Occurs during normal development (e.g. separation of the digits, involution, immune and nervous system
development)

And in response to DNA damage and viral infection

Question 5

GF, CK and interleukins are proteins that do what

Answer 5

Proteins that:

Stimulate proliferation (called mitogens) and maintain survival

Stimulate differentiation and inhibit proliferation e.g. TGFβ

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

Question 6

What are the 3 broad classes of GF, CK and ILs

Answer 6

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

Question 7

Define 4N

Answer 7

4N = cell that has copied all genetic

Material, reflected by X CS

Question 8

Describe analysis of DNA content

Answer 8

DNA labelled w/dye of cells
Dye activated by laser = intensity

X axis = DNA content
Y axis = cell number

Question 9

Describe DNA replication

Answer 9

Semiconservative

Synthesized, 5’ to 3’ direction from dNTP precursors at replication fork by a multienzyme complex,

fidelity is determined by base pairing (A=T, G≡C) and presence of a proofreading enzyme in DNA polymerase

uses an RNA primer and occurs continuously on the leading strand and discontinuously on the trailing strand = Okazaki fragments = ligated after removal of RNA primer

Question 10

Describe prophase

Answer 10

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

Question 11

Describe prometaphase

Answer 11

Nuclear membrane breaks down

Kinetochores attach to spindle in nuclear region

Question 12

Describe metaphase

Answer 12

Chromosomes align in equatorial plane

Question 13

Describe anaphase

Answer 13

Chromatids separate and migrate to opposite poles

Question 14

Describe telophase

Answer 14

Daughter nuclei form

Question 15

Describe cytokenesis

Answer 15

Division of Ct

CS decondense

Question 16

Describe synthesis of thymidine

Answer 16

Methylation of uracil at the 5th carbon by thymidylate synthase

When added to deoxyribose = nucleoside deoxythymidine, synonymous with thymidine

Question 17

Explain the action of S-phase active drugs by giving examples

Answer 17

5-Fluorouracil (an analogue of thymidine blocks thymidylate synthesis)

Bromodeoxyuridine (another analogue that may be incorporated into DNA and detected by antibodies to identify cells that have passed through the S-phase)

Question 18

Explain the action of M-phase active drugs by giving examples

Answer 18

Colchicine (stabilizes free tubulin, preventing microtubule polymerization and arresting cells in mitosis)

Vinca alkaloids (similar action to colchicine)

Paclitaxel (Taxol, stabilizes microtubules, preventing de-polymerization)

Question 19

What is tamoxifen, explain its effects

Answer 19

Tamoxifen - oestrogen receptor antagonist,

… breast cancer cells require oestrogen to work so that they can proliferate

Question 20

Describe the M checkpoint

Answer 20

CS aligned on spindle

Question 21

Describe the G1 checkpoint

Answer 21

Restriction point:
DNA not damaged, Cell size,
metabolite/nutrient stores,

Question 22

Describe the checkpoint before M

Answer 22

DNA completely replicated,

DNA not damaged

Question 23

Describe the importance of the phase after M

Answer 23

Cells responsive to growth factors -

Main site of control for cell growth

Question 24

Describe the regulation of cyclin-CDK activity

Answer 24

Cyclical synthesis (gene expression) and destruction (by proteasome)

Post translational modification by phosphorylation – depending on modification site may result in
activation, inhibition or destruction

Dephosphorylation

Binding of cyclin-dependent kinase inhibitors

Question 25

Describe the role of RB protein in DNA replication

Answer 25

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

Cyclin D-CDK4 + cyclin E-CDK2 = Cyclins lead to phosphorylation of RB = E2F not bound to RB

Released E2F stimulates expression of more Cyclin E and

S-phase proteins e.g. DNA polymerase, thymidine kinase, PCNA etc

DNA replication starts

Question 26

CDK Inhibitory Protein/Kinase Inhibitory Protein (CIP/KIP) family (now called CDKN1):

• Expression stim by what
• Effects

Answer 26

Stimulated weakly by TGFβ + strongly by DNA damage (involving TP53)

Inhibit all other CDK-cyclin complexes

Are gradually sequestered by G1 CDKs thus allowing activation of later CDKs

Question 27

Inhibitor of Kinase 4 family (INK4) (now called CDKN2);

• Stim by
• Role

Answer 27

Expression stimulated by TGFβ

Specifically inhibit G1 CDKs

Question 28

Describe the action of GF

Answer 28

GF binds GFR
Signal transducers activated - cascade of different components
Leading to waves of TF activation

Question 29

What are mitogens

Answer 29

Mitogens = small protein that induces cell to begin cell division

Question 30

Describe the sequential activities in the cycle after mitogen release

Answer 30

When the cells are entering cycle they receive mitogens

Induce expression of early genes (some TF themselves)

Cyclin D1 expression increases

Delayed genes activated, other genes expressed will also induce expression of E2F genes

Responsible for regulating G1-S

Cyclin D expressed when you start expressing E2F2

Question 31

Describe the sequence of events triggered by GF

Answer 31

Growth factor signalling activates early gene expression

Early gene products stimulate delayed gene expression

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

Question 32

Explain the cell being driven through the S-phase and mitosis

Answer 32

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 33

Describe the events after DNA damage

Answer 33

Stop the cycle

(cyclin dependent kinase inhibitors,
CHEK2 etc.)

Attempt DNA repair

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

Programmed Cell Death if repair impossible

(BCL2 family, caspases)

Question 34

Effect of TP53 activation

Answer 34

DNA damaged
Kinase activated
Leads to TP53 (active form)

Leading to:
DNA repair
Repair not possible = apoptosis
Expression of CKI = cell cycle arrest

Question 35

G1 and G1/S cyclin-CDK complexes function

Answer 35

G1 and G1/S Cyclin-CDK complexes phosphorylate RB in the absence of inhibition by CKIs (expression of these is regulated by TP53 or TGFβ)

Question 36

E2F function

Answer 36

E2F released, stimulating expression of genes required for S-phase

Question 37

What happens when all DNA is replicated

Answer 37

If all DNA replicated, G2/M Cyclin-CDK complexes cause cell to enter mitosis

If chromosomes aligned on spindle, exit from mitosis is triggered

Question 38

Effect of cell replicating DNA on S-phase complexes

Answer 38

Cell replicating DNA leads to expression of S-phase Cyclin-CDK complexes