Cell Biology: Cell Parts and Functions

Cell Parts and Functions

• Plasma Membrane: Composed of phospholipids and cholesterol, with proteins embedded or attached; controls entry and exit of substances and has receptor proteins for intercellular communication.

• Nucleus: Enclosed by a double membrane with nuclear pores; contains chromatin and nucleolus; regulates protein synthesis and cell growth.

• Cytoplasmic Organelles:

  • Ribosome: Site of protein synthesis; found attached to endoplasmic reticulum or free in cytoplasm.
  • Rough Endoplasmic Reticulum: Synthesizes proteins and transports them to Golgi apparatus.
  • Smooth Endoplasmic Reticulum: Manufactures lipids, detoxifies chemicals, and stores calcium.
  • Golgi Apparatus: Modifies, packages, and distributes proteins and lipids.
  • Lysosome: Contains digestive enzymes for breaking down waste and foreign substances.
  • Peroxisome: Breaks down fatty acids and amino acids, and detoxifies hydrogen peroxide.
  • Proteasome: Breaks down proteins in the cytoplasm.
  • Mitochondria: Generates energy for the cell through ATP synthesis.
  • Centrioles: Organize microtubules during cell division and form cilia and flagella.
  • Cilia: Moves substances along the cell surface.
  • Flagellum: Propels sperm cells.

Fluid Mosaic Model

• Describes the plasma membrane as a fluid, dynamic structure with proteins and lipids.

Membrane Physiology

• Diffusion: Passive process where particles move from high to low concentration.
• Factors Affecting Diffusion Rate: concentration gradient, temperature, surface area, and diffusion distance.

Types of Diffusion

• Simple Diffusion: Non-polar molecules move through the lipid bilayer.
• Facilitated Diffusion: Integral membrane proteins assist polar or charged molecules.
  • Channel-Mediated Facilitated Diffusion: Ionic channels allow specific ions to pass through.
  • Carrier-Mediated Facilitated Diffusion: Carrier proteins bind to molecules and change shape to transport them.

Active Transport

• Primary Active Transport: Energy from ATP hydrolysis pumps substances against their concentration gradient.
  • Sodium-Potassium Pump: Exchanges sodium ions for potassium ions to maintain cellular balance.
• Secondary Active Transport: Uses energy from ionic gradients to transport substances.

Endocytosis

• Receptor-Mediated Endocytosis: Specific binding of ligands to receptors, followed by vesicle formation and fusion with endosomes.
• Phagocytosis: Engulfing and breaking down large particles, such as bacteria, by phagocytes.
• Bulk-Phase Endocytosis (Pinocytosis): Ingestion of extracellular fluid and solutes.

Exocytosis

• Release of Materials: Vesicles fuse with the plasma membrane, releasing contents into the extracellular fluid.

Transcytosis

• Vesicular Transport: Vesicles move across the cell, releasing contents on the opposite side.

Osmosis

• Net Movement of Solvent: Water molecules move through a selectively permeable membrane from high to low concentration until equilibrium.

Principle of Osmosis

• Water Movement: Water molecules move down their concentration gradient through simple diffusion or aquaporins.

Osmotic Pressure and Tonicity

• Isotonic Solution: Equal concentration of solutes on both sides of the membrane.
• Hypotonic Solution: Lower solute concentration, causing water influx and cell swelling.
• Hypertonic Solution: Higher solute concentration, causing water efflux and cell shrinkage.