Overview
This lecture explains how cancer develops at the cellular level, focusing on cell life spans, genetic mutations, causes of cancer, and key characteristics of the disease.
Human Cells and Lifespan
- The human body contains 50–75 trillion cells, which are constantly dying and being replaced.
- Red blood cells live about 4 months, white blood cells over a year, colon cells around 4 days, and brain cells last a lifetime.
Cancer Development and Tumors
- Cancer begins when a single cell grows and multiplies uncontrollably, forming a mass called a tumor.
- The original site where abnormal cell growth starts is called the primary tumor.
Genes, DNA, and Cell Division
- Genes are sequences of DNA coding for proteins or RNA that control cell function, division, and death.
- During mitosis (cell division), DNA replicates and may develop mistakes called mutations.
Mutations and Their Effects
- Mutations often have no effect if they occur in non-coding DNA, but some can cause increased cell division or prevent normal cell death.
- Typically, at least six mutations in coding DNA are needed for a normal cell to become cancerous.
Causes of Mutations and Cancer
- Cells have repair mechanisms, but accumulated genetic damage increases cancer risk.
- Mutations happen naturally but can also be caused by lifestyle factors such as exposure to carcinogens (cancer-causing substances) like tobacco smoke.
- Over 80% of lung cancer cases are attributed to smoking.
- Genetics can play a role; faulty genes like BRCA1 and BRCA2 increase the risk of inherited breast cancer.
- Exposure to radiation, UV radiation from the sun, and certain environmental chemicals can also cause mutations.
Summary and Nature of Cancer
- Cancer results from DNA changes that lead to uncontrolled mitosis and tumor formation.
- It is a non-communicable disease, meaning it cannot be transmitted between individuals.
Key Terms & Definitions
- Cancer — Uncontrolled growth and division of abnormal cells, forming tumors.
- Tumor — A mass of abnormal, rapidly dividing cells.
- Primary tumor — The original site where cancerous growth begins.
- Gene — A DNA sequence coding for a protein or RNA molecule.
- Mutation — A change in DNA sequence, sometimes leading to abnormal cell behavior.
- Carcinogen — Substance capable of causing cancer in living tissue.
- Mitosis — The process by which a cell divides, producing two new cells.
- Non-communicable disease — A disease that is not infectious or transmissible between people.
Action Items / Next Steps
- Review main causes and risk factors for cancer.
- Learn key genetic terms and the process of mutation.
- Understand the difference between communicable and non-communicable diseases.