Introduction to Cell Biology

Cell Structure and Function

Cell Membrane

The cell membrane is a dynamic structure known as the fluid mosaic model, consisting of:

• Phospholipid Bilayer: Forms the basic structural framework.
• Proteins: Integral proteins (embedded in the membrane) and peripheral proteins (attached to the membrane surface).
• Cholesterol: Provides stability and regulates fluidity.
• Carbohydrates: Often attached to proteins (glycoproteins) or lipids (glycolipids) for cell recognition.

Energy Flow and Metabolism

• Energy Flow: From sunlight to producers (photosynthesis) and then through consumers (cellular respiration).
• Matter Cycling: Carbon, nitrogen, and other elements cycle through living organisms and the environment.
• Metabolism Types: Anabolism (building molecules) and Catabolism (breaking down molecules).
• Controls: Inhibition (competitive, non-competitive) and substrate concentration affect enzyme activity.

Photosynthesis

6 CO₂ + 6 H₂O → C₆H₁₂O₆ + 6 O₂

Steps: Light-dependent reactions (thylakoid) and light-independent reactions (stroma).

Cellular Respiration

C₆H₁₂O₆ + 6 O₂ → 6 CO₂ + 6 H₂O

Steps: Glycolysis, Krebs cycle, Electron Transport Chain

Cell Division

Mitosis

• Interphase: Cell prepares for division.
• Prophase: Chromosomes condense, nuclear envelope breaks down.
• Metaphase: Chromosomes align at the cell's equator.
• Anaphase: Sister chromatids separate and move to opposite poles.
• Telophase: Chromatids reach poles, nuclear envelope reforms, cytokinesis begins.

Cell Cycle

• Interphase: G1 (cell growth), S (DNA synthesis), G2 (preparation for division).
• Mitosis: Prophase, Metaphase, Anaphase, Telophase.
• Cytokinesis: Division of the cytoplasm.

Chromosome Number

• Somatic Cells: Diploid (2n), containing pairs of homologous chromosomes.
• Gametes: Haploid (n), containing half the chromosome number.

Meiosis

• Meiosis I: Prophase I, Metaphase I, Anaphase I, Telophase I.
• Meiosis II: Prophase II, Metaphase II, Anaphase II, Telophase II.

• Meiosis: Reduces chromosome number, produces gametes for sexual reproduction.
• Mitosis: Maintains chromosome number, used for growth, repair, and asexual reproduction.

Genetics

Inheritance Patterns

• Incomplete Dominance: Blending of traits (e.g., pink flowers from red and white parents).
• Co-dominance: Both alleles expressed (e.g., blood types A, B, AB).
• Epistasis: One gene masks the effects of another.
• Sex-Linked Traits: Located on sex chromosomes.
• Polygenic Traits: Influenced by multiple genes.
• Multiple Alleles: More than two alleles for a gene.

Protein Synthesis

• Transcription: DNA to RNA (in the nucleus).
• Translation: RNA to protein (in the cytoplasm).