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

Mitosis and Cancer

v     Objectives

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)

  Ř      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


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:


·        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




·        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:




§         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.






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.

Immunological treatment: