Biology Unit 5: Part 1 - Regulating the Cell Cycle

Controls on Cell Division

The cell cycle is controlled by ^^regulatory proteins^^ both inside and outside of the cell. The controls on cell growth and division can be ^^turned on and off^^. For example, When an injury such as a broken bone occurs, cells are stimulated to divide rapidly and start the healing process. The rate of cell division slows the during the healing process. Cell cycle regulators are proteins that control the progression of a cell through the cell cycle and can either ^^stimulate^^ or ^^inhibit^^ cell cycle progression.

Genes that encode these proteins are referred to as proto-oncogenes and tumor suppressor genes; ^^mutations in these genes^^ can lead to cancer.

  • Stimulating proteins → encoded by ^^proto-oncogenes^^

  a. Only ^^one^^ copy of the mutated gene is needed to produce ^^oncogenes^^ and eventually tumor cells.

  • Inhibitory proteins → encoded by ^^tumor suppressor genes^^

  a. ^^Two^^ mutated copies of the gene is needed to produce non-functioning TSG

Regulating Genes

  1. Proto-oncogenes

   a. The most important cell cycle regulators are the cyclin-dependent kinases ^^(CDKs)^^ and ^^cyclins^^.

   b. Normally, proto-oncogenes code for proteins that regulate the cell cycle by ^^stimulating cellular growth^^ and division.

   i. Analogy is gas pedal.

   c. When there is a mutation in this gene, called ^^oncogenes^^, the cell is continuously dividing.

   i. Analogy is gas pedal is stuck accelerating.

  1. Tumor Supressor Genes
  • Code for proteins that ^^restrict cellular growth^^ and division or even promote ^^programmed cell death^^.

  i. Analogy is brake pedal.

  • When there is a mutation in this gene, cells ^^cannot turn off^^ cell division.

  i. Analogy is broken brakes.

  • ^^P53^^ is important in G1 & G2 checkpoints. If DNA is damaged, it can pause the cell cycle or initiate cell death.

  ^^P53^^ is a gene that makes a protein that is found inside of the nucleus in cells and plays a key role in controlling cell division and death.

  • ^^ATM^^ normally stops the cell cycle so that damaged DNA can be fixed. A mutation in the gene that codes for ATM is associated with developing cancer, particularly ^^leukemia^^ and ^^lymphomas^^.
  • ^^BRCA1^^ normally meditates DNA repair. Mutation in this gene are involved in the development of ^^breast^^ and ^^ovarian^^ cancers.

  i. common genetic testing can be done to determine if an individual carries the BRCA1 gene.

HeLa Cells

A HeLa cell is a cell type in an ^^immortal^^ cell line used in scientific research. Cells were from cervical cancer cells taken from ^^Henrietta Lacks^^, a patient who eventually died of her cancer on October 4, 1951.

Cell Death

Cells end their life cycle in one of two ways:

  1. A cell may die by accident or due to damage or injury.
  2. A cell may be programmed to die = ^^apoptosis^^
       * plays a role in development by shaping the structure of tissues and organs in plants and animals.
       * For example, the foot of a mouse is shaped the structure of tissues and organs in plants and animals.
       * When apoptosis occurs does not occur as it should, a number of diseases can result.
         * For example, the cell loss seen in ^^Alzheimer’s^^ and ^^Parkinson’s^^ disease can result from ^^too much apoptosis^^.

Cancer: Uncontrolled Cell Death

^^Cancer^^ is a disorder in which body cells lose the ability to control cell growth. Cancer cells do not respond to the signals that regulate the growth of most cells. As a result, the cells divide uncontrollably to form a mass of cells called a ^^tumor^^. Not all tumors are cancerous, some are ^^benign^^ or ^^non-cancerous^^. Benign tumors do NOT spread to surrounding tissue. ^^Malignant^^, or ^^cancerous^^, tumors invade and destroy surrounding healthy tissue and spread to other parts of the body. When cancer cells break away from the original tumor, enter the bloodstream, and form new tumors in another location is called ^^Metastasis^^. Cancer cells absorb nutrients needed by other cells, block nerve connections, and prevent organs from functioning.

What Causes Cancer?

Cancers are caused by ^^defects in genes (mutations)^^ that repair damaged DNA and that regulate cell growth and division.

  • Some sources of gene defects:
      * Exposure to ^^environmental factors^^ like smoking tobacco, radiation, and UV light.
      * ^^Inheritance^^ of defective genes from parents
      * Viral infections ^^(HPV can cause cervical concern)^^
      * ^^Errors^^ made during normal cell division.

Treatments for Cancer

  1. ^^Chemotherapy^^ is the use of compounds that kill or slow the growth of cancer cells.

   a. Because most chemotherapy compounds target ^^rapidly dividing cells^^, they also interfere with cell division in normal, healthy cells.

   i. This can produce ^^serious side effects^^.

  1. Some localized tumors can be removed by ^^surgery^^

   a. ^^Lumpectomy^^ is the removal of a breast tumor

   b. ^^Mastectomy^^ is the removal of a breast tissue.

  1. Many tumors can be treated with target ^^radiation^^.

   
   4. Immunotherapy

      a. Uses the body’s own ^^immune system^^ to recognize and kill cancer cells.

      b. There are different types of immunotherapies and the side effects are different among patients.

      c. Most of the side effects are similar to the symptoms you experience with an ^^infection^^

      d. In some individuals their heightened immune system can also begin attacking ^^healthy^^ cells.