Cell Cycle Regulation 1

Cell-cycle Control & DeathChapter 18

You will not be responsible for: details of S-CdK functionmechanisms of spindle assembly and anaphasespecific details of the caspase cascade & bcl-2 familytopics on extracellular signals (pp 636- 640) not covered in class

Review mitosis on your own Panel 18-1, etcRead on your own about cytokinesis in plant and animal cells pp 630 - 633

Questions in this chapter you should be able to answer:

Chapter 18: 1 - 5, 10, 12, 13, 14, 16, 17, 20, 25, 26 all but C, 28, 30

Cell Cycle Regulation 2

How is cell division and growth regulated?

Growth factors-- stimulate cell growth

Mitogens-- trigger cell division-- e.g., EGF, phytoestrogens

Survival signals-- disable apoptotic mechanisms

Cell Cycle Regulation 3

What are the stages of the cell-cycle?-- a review

G1

S

G2

M

G0

Table 18–1 Some Eucaryotic Cell-Cycle TimesCell type Cell cycle timeEarly frog embryo cells ~30 minutesYeast cells 1.5–3 hoursIntestinal epithelial cells ~12 hourscultured fibroblasts ~20 hoursHuman liver cells ~1 year

Cell Cycle Regulation 4

How is progress through cell cycle regulated?

“Cell-cycle control system”

The ‘Checkpoint’ model-- not a ‘domino’ process

How are they controlled? -- intracellular and extracellular signals

What are the effectors -- lots of kinases & phosphatases

Cell Cycle Regulation 5

How is cell cycle progress studied?

Different systems-- yeast: cell cycle mutations-- frog: big dividing embryos-- sea urchin & clam: many embryos

Asynchronously dividing cells DNA/nucleus staining Flow cytometry

Synchronously dividing cells

Ques 18-2Where are G1,S,G2, & M stage cells?

DAPI stained cells

Cell Cycle Regulation 6

What did study of frog embryos reveal about the control system?

Be sure to read How we know

Frog egg cytoplasmic transfer experiments

Something in the cytosol triggers mitosis

-- called MPF

Activity of MPF oscillates during the cell cycle

What is MPF?

Cell Cycle Regulation 7

What did sea urchin & clam embryos reveal?

Population of synchronously dividing embryos

S35 labeling, SDS-PAGE, autoradiography

Revealed cyclic synthesis & breakdown of certain proteins

Called cyclin

Cell Cycle Regulation 8

What do we know about MPF & cyclin?

MPF is a cyclin bound to a Cdk ‘cyclin-dependent protein kinase’

= M-Cdk

Several Cyclins and Cdks -- regulate different cell cycle events

Table 18–2 The Major Cyclins and Cdks of Vertebrates

Cyclin–Cdk Complex Cyclin Cdk partner G1-Cdk cyclin D Cdk4, Cdk6 G1/S-Cdk cyclin E Cdk2 S-Cdk cyclin A Cdk2 M-Cdk cyclin B Cdk1

Cell Cycle Regulation 9

How is cyclin-CDK activity regulated?

Two processes

1. Synthesis & destruction of cyclin

-- ubiquination-- proteasomes

2. Inactivation & activation-- Activating/inhibitory Kinases/phosphatase

-- Pos feedback rapid activation

Cell Cycle Regulation 10

How do cyclin-cdk’s trigger cellular events?

S-Cdk triggers DNA replication-- activates replication origins-- blocks reactivation

What does activated M-CDK do?

1) Phosphorylates H1 histone (triggering C’some condensation)

2) Disassembly of nuclear lamina3) Changes behavior of microtubules

-- phosphorylates MAPs4) etc…??

Cell Cycle Regulation 11

How does activated S-Cdk trigger DNA replication?

Origin of Replication Complex (ORC)

CDC-6 rises during G1-- helps build replication fork complex-- helicase, polymerase, etc

S-CDK activates replication complex-- inhibits ORC

Cell Cycle Regulation 12

How is cyclin-Cdk coupled to checkpoint control?

Tumor suppressor genes-- inactivation can dispose cell toward tumor formation

-- P53, P21 and Rb are all TSGs

-- loss of both alleles necessaryWhy?

P53 can also trigger apoptosis

Figures 18-14 + 18-15

Cell Cycle Regulation 13

What is Apoptosis?-- “programmed cell death”

Apoptosis vs necrosis

When does apoptosis occur?

Normal organism / cell develop

damaged/ infected/ cancerous cells

Sculpting of mouse paw

Question 18-10, p 635Why apoptosis rather than

necrosis?

Apoptosis

Cell Cycle Regulation 14

What are the mechanism of apoptosis activation and cellular destruction?

Intrinsic vs extrinsic activation

Caspase family of proteases-- activation ‘cascade’

Intrinsic activation signals-- cell injury, P53 activation, etc-- lack of survival signal

Extrinsic activation signals-- cell-surface receptors (Fas/FasL)-- cellular toxins (Granzymes)

Caspase cascade

Intrinsic pathway