Fluid Mosaic Model, Cellular Organelles, Mitosis, and Protein Synthesis

1. Components of the Plasma Membrane and Fluid Mosaic Model

  • Fluid Mosaic Model: Describes the plasma membrane as a dynamic, flexible structure composed of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

  • Phospholipid Bilayer:

    • Phospholipid:

    • Phosphate Head: Hydrophilic (water-loving) region, facing the aqueous extracellular and intracellular environments.

    • Lipid Tail: Hydrophobic (water-fearing) region, oriented inward away from water.

    • Hydrophilic Regions: Composed of polar phosphate heads.

    • Hydrophobic Regions: Composed of nonpolar fatty acid tails.

  • Membrane Proteins:

    • Integral Proteins: Penetrate the hydrophobic interior of the lipid bilayer, spanning the membrane completely or partially.

  • Cholesterol: Embedded within the phospholipid tails to regulate membrane fluidity and stability.

  • Glycocalyx: Carbohydrate coat on the outer surface of the cell membrane, involved in cell recognition and protection.

2. Cellular Organelles and Functions

  • Cytoskeleton: Provides structural support, maintains cell shape, and facilitates intracellular transport.

  • Nucleus: Houses genetic material (DNA) and directs cellular activities including gene expression.

  • Nucleolus: Site of ribosome synthesis and assembly within the nucleus.

  • Golgi Apparatus (Golgi Complex): Modifies, sorts, and packages proteins and lipids for transport or secretion.

  • Lysosome: Contains digestive enzymes to break down waste, cellular debris, and pathogens.

  • Proteasome: Degrades unneeded or damaged proteins via proteolysis.

  • Peroxisome: Contains enzymes that oxidize toxic substances, including fatty acids and hydrogen peroxide.

  • Ribosome: Site of protein synthesis, translating mRNA into amino acid sequences.

  • Rough Endoplasmic Reticulum (Rough ER): Studded with ribosomes; functions in protein synthesis and folding.

  • Smooth Endoplasmic Reticulum (Smooth ER): Synthesizes lipids, metabolizes carbohydrates, and detoxifies chemicals.

  • Mitochondria: Double-membrane organelle responsible for cellular respiration and ATP production.

  • Cytoplasm: Cellular region between the plasma membrane and nucleus, containing cytosol and organelles.

3. Stages of Mitosis

  • Prophase: Chromatin condenses into chromosomes; nuclear envelope breaks down; mitotic spindle forms.

  • Metaphase: Chromosomes align along the metaphase plate, attached to spindle fibers.

  • Anaphase: Sister chromatids are separated and pulled toward opposite poles of the cell.

  • Telophase: Chromosomes decondense; nuclear envelopes reform around two new nuclei.

4. Protein Synthesis

  • Transcription:

    • Occurs inside the nucleus.

    • DNA sequence is transcribed into a complementary messenger RNA (mRNA) strand.

    • mRNA exits the nucleus through nuclear pores into the cytoplasm.

  • Translation:

    • Occurs in the cytoplasm at ribosomes (free or bound to Rough ER).

    • Ribosomes read mRNA codons, and transfer RNA (tRNA) delivers matching amino acids.

    • Amino acids bond to form a growing polypeptide chain (protein).