Sexual v. Asexual Reproduction

Binary Fission

Chromosome Structure• Eukaryotic chromosomes contain DNA and

protein tightly packed together to from chromatin.

• Chromatin consists of DNA tightly coiled around proteins called histones.

• DNA & histone molecules form nucleosomes, which pack together to form thick fibers of chromosomes.

The Cell Cycle

Mitosis

Whitefish Blastula

Mitosis in Plant Cells

Onion Root Tip

Controls on the Cell Cycle:

Some cells stop dividing when mature (stay in G0)

ex) many neurons (nerve) & muscle cells Others divide for growth & repair Influences of cell division:

Growth factors – protein that stimulates cell division Density-dependent inhibition (cell to cell contact) Anchorage dependent

Cell Cycle Regulators:• Proteins called cyclins start/stop the

cell cycle.• The cycle is regulate by various

factors:1. Intracellular factors:

- All chromosomes are replicated- All spindles are attached

2. Extra-cellular factors: - Binding of growth factors- Cell to cell contact

Growing Out of Control: Cancer

• Cancer is a disease of the cell cycle• Cells do not respond normally to controls of

the cell cycle system• Tumor: abnormally growing mass of body

cells– Benign: abnormal cells remain at original sight

forming a lump; although can cause problems, normally can be fully removed by surgery

– Malignant: spread, displacing normal tissue and disrupting organ function

– Metastasis: spread of cancer cells via circulatory system transport

Molecular Basis of Cancer:• Tumor Suppressor Genes: (p53) - genes that normally halt the cell cycle

- problem if stuck “OFF” (cells keep dividing)

• Oncogenes: - genes that tell cells to divide

- problem if stuck “ON” (cells keep dividing)

Cancer categorized based on site of origin:

• Carcinoma: originate in internal or external coverings of the body (skin or lining of intestine)

• Sarcoma: Arise in support tissue (bone or muscle)

• Leukemia: Arise in blood or bone marrow (abnormal number of white blood cells)

• Lymphoma: Arise in lymphatic cells of the immune system (lymph nodes or spleen)

Treating Cancer

• Localization and surgical removal of tumor

• Radiation: – Damages DNA in cancer cells more than normal cell– Cancer cells do not have the ability to repair– Cancer cells die without dividing/reproducing

• Chemotherapy: (For widespread or metastatic tumors) – Chemicals that disrupt specific steps in the cell cycle

• freezes the mitotic spindle• prevents formation of spindle• Damage DNA or RNA involved in making growth

factors