lecture 5 continued

DNA Mutation and Cancer

• Thymine Dimer Formation

  • Caused by prolonged sun exposure, especially in lighter-skinned individuals.

  • Two thymine (T) bases fuse together, altering the DNA sequence.

  • Original codon (TAA) changes to TAG, leading to a different amino acid.

  • Results in a point mutation, affecting subsequent amino acids in the protein chain.

• Role of Polymerases in Correction

  • DNA polymerase and RNA polymerase help repair DNA mutations.

  • In younger organisms, these enzymes are more effective in repairing UV-induced damage.

  • As organisms age, the efficacy of these repair mechanisms declines, increasing cancer risk.

• Cancer Cell Replication

  • Cancer cells replicate rapidly, characterized by abnormal divisions.

  • Chemotherapy targets rapidly dividing cells, which can inadvertently damage healthy cells, leading to side effects such as hair loss and nausea.

Epithelial Tissue

• Characteristics of Epithelial Cells

  • Undergo mitosis, allowing for rapid cell turnover and repair.

  • Form protective layers, lining internal cavities and organs.

  • Avascular—lack blood vessels and receive nutrients via interstitial fluid surrounding them.

• Types of Epithelial Tissue

  • Simple vs. Stratified:

    • Simple epithelium: Single layer (e.g., lining of blood vessels).

    • Stratified epithelium: Multiple layers (e.g., skin).

  • Glandular Epithelium Types:

    • Merocrine: Secrete without losing cellular material (e.g., sweat glands).

    • Apocrine: Part of the cell is lost during secretion (e.g., some mammary glands).

• Structure and Function

  • Epithelial cells produce secretions (e.g., hormones, enzymes).

  • Cells have exposed and attached surfaces; basement membrane anchors them to connective tissue.

Skin Layers and Functions

• Stratum Basalis:

  • Basal layer of skin where mitosis occurs, pushing new cells up.

• Stratum Granulosum:

  • Cells begin producing keratin, involved in skin's protective barrier.

• Stratum Lucidum:

  • A thin layer present in thick skin, where cells start dying off as they fill with keratin.

• Stratum Corneum:

  • Outermost layer composed of dead, keratinized cells acting as a barrier to protect against pathogens and water loss.

• Dermal Papillae:

  • Protrusions that enhance grip and sensitivity, leading to fingerprints.

• Meissner's Corpuscles:

  • Nerve endings located within dermal papillae, sensitive to light touch—aids in tactile perception.

Additional Notes

• Hyaluronic Acid:

  • Often marketed as a skin rejuvenating agent, but primarily serves as a cement for holding cells together.

• Merocrine vs. Apocrine Glands:

  • Secretory function related to body odor; pheromones can influence social interactions subconsciously.

• Understanding Cancer Treatments:

  • As polymeases decline with age, the risk of cancer increases due to insufficient DNA repair.

• Chemotherapy:

  • Works by targeting rapidly dividing cells, including both cancerous and normal cells, leading to side effects.