Cell Cycle Guided Reading Questions

Review

https://www.youtube.com/watch?v=xukDIWFMU9Y

Just a few facts!

Intestinal cells- divide more than 2X day

Nerve and muscle cells- never divide always in GO

Human liver- divides 1X year but will divide more if needed for repair

Mitosis Promoting Factor (MPF) low in early G2 rising throughout the phase and peaks in mitosis

2 subunits:1.Protein kinase –

[constant]; catalyzes phosphorylation

2.Cyclin – [increases]; regulatory proteins that binds to kinase

Cdk -Cyclindependent kinase

**Dimer activates MPF

Activated MPF initiates production of several proteins (G2 phase)

a) Chromosomal proteins – initiates M phase

b) Lamins –initiates breakdown of nuclear envelope (fibrous proteins)

c) Microtubule associated proteins – activate mitotic spindle?

d) Enzyme degrading cyclin – deactivate MPF

• sufficient nutrients• GF’s (growth

factors) present• DNA undamaged•Size of cell

Cell Cycle Regulated by 3 checkpoints(controlled by Cdk enzymes)G1/S Checkpoint

G2 /M Checkpoint

•DNA undamaged

Spindle (Metaphase )Checkpoint

Cell Cycle Control Animationhttps://www.youtube.com/watch?v=JcZQkmooyPk

Cell Cycle Pathways

**Growth factors act as social controls**(if deprived of growth factors cells remain in G0)

In normal cells:• GF’s rcvd from surrounding cells bind to receptors

• induce cyclin production

• cell division initiated

In abnormal cells:• GF’s not needed for growth/division

• pathway disrupted• overproduction of cyclin (↑ division)• defective “brake proteins” can not suppress growth → tumors • benign• malignant (metastasis)

•Oncogenes- the gene that when mutated or in abnormal increased levels can promote unregulated stimulated growth (contribute to cancer)

Stages of Mitosis Animation

Healthy Cells

~ normal growth~ GF’s

~ Adhere to nearby cells~ Regulation

Cancerous Cells

~ Rapid growth/divisi

on~ invasive ~ damage

healthy cells~ No controls

Both~ grow~ divide

Mutations in the cell cycle signaling are responsible for many cancers.Image taken from: www.ravenbiology.com Ebook figure 10.24

Cancer is a disease of the cell cycle

The environment:

Some environmental agents associated with cancer are: • Viruses • Tobacco smoke • Food • Radiation • Chemicals • Pollution

VirusesViruses—mostly in the form of DNA viruses—have been causally linked to cancer.

• human papillomaviruses—primarily types 16 and 18, which are sexually transmitted—have been linked to cervical cancer;

• more than 25 other types of papillomaviruses have been linked to cancer as well

• hepatitis B and C—linked to cancer of the liver • human immunodeficiency virus (HIV)—linked to Kaposi's

sarcoma and lymphoma • retroviruses—linked to cancers in animals other than

humans

Tobacco smoke

• is associated with 50% to 60% of all cancer deaths• is causally linked to cancers of the lung, upper respiratory

tract, oesophagus, bladder, pancreas • is probably a cause of cancer of the stomach, liver,

kidneys, colon, and rectum

Pollution

Pollution has been difficult to document as a contributor to human cancer.

However, long-term exposure to high levels of air pollution may increase lung cancer risk by as much as 25%.