Introduction to Cell Biology

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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.


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


  • 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 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.


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).

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