Mitosis and Cancer

A & P Subject: Cells II: The Cell Cycle and Cancer

Mitosis and Cancer

v Objectives

Ø The cell life cycle

§ List the phases of the cell life cycle and key events related to each phase.

Ø Developmental aspects

§ Describe the normal route to cellular differentiation

§ Compare theories of cell differentiation and aging

§ Learn special vocabulary for cancer.

v The Cell Life Cycle - The Cell Cycle

Ø Interphase, mitosis, and in specialized cases meiosis (not discussed at this time)

Ø Interphase

§ Phase between cell divisions

§ Period of cell growth and normal ongoing metabolic (chemical) activities

· G₁: metabolic activity and vigorous growth

· G₀: cells that permanently cease dividing

· S (synthesis): DNA replication

· G₂: preparation for division

Ø Mitosis: process necessary for cell division into two identical cells (replacement) Division of the nucleus

http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells3.html

http://www.accessexcellence.org/RC/VL/GG/mitosis.html

§ Goal: Exact and equal division of replicated DNA

§ Important events of each mitotic stage:

· Prophase

¨ Chromosomes condense

¨ Nuclear membrane breaks up

¨ Microtubule spindle forms

· Metaphase

¨ Spindle microtubules attach to sister chromatids

¨ Sister chromatids align along metaphase plate

¨ Get tug-of-war, and with proper tension, move to anaphase

· Anaphase

¨ Attachments between sister chromatids break

¨ Sister chromatids migrate to opposite spindle poles

¨ We now have independent daughter chromosomes

· Telophase

¨ Chromosomes arrive at opposite spindle poles

¨ They decondense

¨ Microtubule spindle breaks down

¨ Nuclear envelope reforms

http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells3.html

http://micro.magnet.fsu.edu/micro/gallery/mitosis/mitosis.html

http://www.northarundel.com/aniplayer/index.htm

· Cytokinesis

¨ Cleave furrow and contractile ring form via microfilaments

¨ Cytoplasm splits

¨ Two new daughter cells (genetically identical to parent cell) are formed

Animation of Mitosis:

http://www.cellsalive.com/mitosis.htm

QUICK QUIZ

http://micro.magnet.fsu.edu/micro/gallery/mitosis/mitosis.html

§ Some chemotherapy drugs target the stages of mitosis

§ The developmental aspects of cells: life after mitosis

· Differentiation: While all cells originate from one fertilized egg (one cell) they respond to different chemical signals and form 4 major tissue groups: epithelial, connective, muscle or nervous tissue.

· Once a cell divides, the two new cells should follow their DNA instructions and function as the old cell once did, as a member of a tissue.

Ø The issue of aging: why cells quit doing their jobs

¨ Cellular clock: after a certain amount of time or certain number of cell divisions, cells die.

¨ Programmed cell death (apoptosis)

¨ Free radical detoxification slows as we (our organelles) age, thereby hastening cell death

¨ Pieces of telomeres, DNA structures on the ends of chromosomes, break off during mitosis and so limit the amount of times mitosis can occur in a cell line. Replacement is limited.

Ø Understanding Cancer: uncontrolled division and spread of cells in the body

· Neoplasm (a more general term): abnormal mass of growing cells

¨ Benign tumor: cells are encapsulated, growing but not spreading

Ø Often cells functioning correctly in the wrong body area like fat tumors. Can often remove before they pressure other organs.

¨ Malignant (cancerous) tumor:

Definition: Cancer is abnormal cell division which results in excessive growth, a tumor.

§ Unregulated cell growth

· Cells no longer respond to normal control mechanisms

· They no longer heed to normal signals that regulate cell cycle

· They no longer exhibit density-dependent (contact) inhibition

· They do not stop dividing when growth factors are depleted

§ Cells spread throughout the body and the term “metastasis” is used.

§ During mitosis, if a mistake is made, some sections of DNA sense it and halt the replication process, killing the cell (tumor suppression genes)

§ If these genes are not present or functioning, cells with improper DNA sequences can survive mitosis. Some will die off, others will begin to divide uncontrollably and give rise to cancer.

· How do these genes become damaged?

¨ Carcinogens – agents that cause mutations in the DNA

¨ Examples: radiation, mechanical trauma, certain viral infections, and many chemicals (tobacco tars, saccharine, etc.)

§ Cancers kill by displacing and putting pressure on normal tissues, cutting off their blood supply and/or interrupting organ function.