A & P Subject: Cells II: The Cell Cycle and Cancer
Mitosis and Cancer
Ř The cell life cycle
§ List the phases of the cell life cycle and key events related to each phase.
Ř 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
Ř Interphase, mitosis, and in specialized cases meiosis (not discussed at this time)
§ 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
Ř Mitosis: process necessary for cell division into two identical cells (replacement) Division of the nucleus
§ Goal: Exact and equal division of replicated DNA
§ Important events of each mitotic stage:
¨ Chromosomes condense
¨ Nuclear membrane breaks up
¨ Microtubule spindle forms
¨ Spindle microtubules attach to sister chromatids
¨ Sister chromatids align along metaphase plate
¨ Get tug-of-war, and with proper tension, move to anaphase
¨ Attachments between sister chromatids break
¨ Sister chromatids migrate to opposite spindle poles
¨ We now have independent daughter chromosomes
¨ Chromosomes arrive at opposite spindle poles
¨ They decondense
¨ Microtubule spindle breaks down
¨ Nuclear envelope reforms
¨ Cleave furrow and contractile ring form via microfilaments
¨ Cytoplasm splits
¨ Two new daughter cells (genetically identical to parent cell) are formed
Animation of Mitosis:
§ 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.
Ř 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.
Ř 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
Ř 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.
Major Types of Cancer
Cancer rates in California
· Diagnosis and treatments
¨ Biopsy: Sample of suspect tissue is surgically removed and examined microscopically for malignant cells
¨ Surgical removal of the tumor
¨ X-ray treatment of surrounding local area to kill metastasized cells
¨ Chemotherapy to find and destroy cells that have escaped body wide.