Cancer and Cell Division
Introduction to Cancer and Cell Division
What is Cancer?
Unregulated cell division leading to tumors.
Tumors can be:
Benign: Non-cancerous, no harmful effect on surrounding tissues.
Malignant: Cancerous, invades surrounding tissues.
Metastatic: Individual cancer cells break away and form new tumors.
Impact of Cancer
Approximately 1500 new diagnoses daily in the U.S.
Nearly 40% of Americans will be diagnosed; about half will die from it.
Significant financial resources dedicated to cancer research.
Cell Division Essentials
Cells must divide for growth and repair.
Continuous replacement of shed cells (skin/intestines).
Sex cells are produced through division that reduces chromosomes by half.
The Cell Cycle
Definition: Series of changes a cell undergoes from formation to reproduction.
Comprised of:
Interphase: Cell growth and normal function.
Mitotic Phase: Cell division resulting in two daughter cells.
Interphase Phases
G1 (Gap 1):
Active protein synthesis, organelle increase, cell growth.
Non-dividing cells enter G0 stage until division is needed.
S Phase:
DNA replication, ensuring each daughter cell has a copy of DNA.
G2 (Gap 2):
Final preparations before cell division.
DNA and Chromosomes
Structure: DNA tightly coiled around proteins (histones), forming chromosomes.
Each chromosome can extend nearly 7 feet when uncoiled.
Chromosome Types:
Unduplicated: One chromatid, uncoiled.
Duplicated: Two sister chromatids, X-shaped structure.
Cell Division Events
Mitosis: Division of nuclear material (chromosomes).
Cytokinesis: Division of cytoplasm and cellular contents.
Mitosis Phases
Prophase: Chromosomes condense, nuclear membrane disappears, spindle fibers form.
Metaphase: Chromosomes align at the cell equator.
Anaphase: Sister chromatids are pulled apart; cell elongates.
Telophase: Chromosomes uncoil, nuclear envelope reforms; cytokinesis begins.
Differences in Cytokinesis
Animal Cells: Formation of a cleavage furrow.
Plant Cells: Formation of a cell plate due to rigid cell walls.
Regulation of the Cell Cycle
Checkpoints: Critical for normal cell division, cancers arise from malfunctioning checkpoints.
Cyclins: Proteins controlling cell cycle events.
Oncogenes: Mutated genes that promote uncontrolled division.
Tumor Suppressor Genes: Prevent division under unfavorable conditions, mutations lead to continuous division.
Cancer Development
Multiple Hit Model: Cancer arises from several mutations over time.
Risk Factors:
Lifestyle choices: Smoking (30% of deaths), diet, UV exposure.
Age: Risks accumulate over time.
Genetic predisposition: Certain cancers run in families but many cases are sporadic.
Cancer Treatments
Chemotherapy: Targets actively dividing cells; affects both cancerous and healthy rapidly dividing cells.
Radiation Therapy: High-energy particle usage to destroy cancer cells; damages their DNA.
Introduction to Meiosis
Meiosis: Process of forming gametes (ova and sperm) with half the chromosome number (haploid).
Importance: Genetic variability and reduced chromosome number for reproduction.
Meiosis Process
Meiosis I: Homologous chromosomes separate.
Meiosis II: Sister chromatids separate.
Result: Four genetically different haploid cells.
Genetic Variation in Meiosis
Crossing Over: Exchange of genetic material between homologous chromosomes in Prophase I.
Random Alignment: Chromosomes align independently at the metaphase plate during Metaphase I to increase genetic diversity.
Mistakes During Meiosis
Nondisjunction: Failure of chromosomes to separate properly, leading to gametes with abnormal chromosome numbers.
Consequences: Conditions like Down syndrome occur due to trisomy (extra chromosome).
Infertility and Meiosis
Sperm health declines due to lifestyle factors (heat, pollution).
Women are born with a finite number of eggs, which undergo Meiosis I during ovulation and Meiosis II only if fertilization occurs.
Conclusion
Understanding mitosis and meiosis is critical for comprehending cancer development and reproductive processes.