Biology Lipids and Phospholipids

Lipids and Phospholipid Molecules

• Phospholipid bilayer consists of polar heads and non-polar tails; heads face outward, tails inward.
• Polar heads are hydrophilic (water-loving) and negatively charged, while non-polar tails are hydrophobic (water-fearing) and uncharged, made of fatty chains.
• Properties of water explain the attraction to charged heads and repulsion by uncharged tails.
• Phospholipids twirl and vibrate within their half of the bilayer; they rarely switch from intracellular (ICF) to extracellular (ECF) without cell distress.
• The bilayer's primary function is to separate intracellular and extracellular compartments.

Fluid Mosaic Model

• Characterized by fluidity (moving, not rigid) and mosaic nature (composition is not uniform).
• Phospholipids are 50 times more abundant than proteins, though proteins make up more than half the membrane mass.

Protein Types in Plasma Membrane

• Various protein shapes and sizes determined by function.
• Types include:
  • Channels: permit transport of ions or molecules.
  • Carrier Modules: aid in the transfer of specific substances like glucose.
  • Docking Marker Acceptors: essential for cellular process.
  • Membrane Bound Enzymes: facilitate biochemical reactions.
  • Receptors: responsible for receiving signals.
  • Cell Adhesion Molecules (CAMs): involved in cell-to-cell adhesion.

Cell-to-Cell Adhesions

• Plasma membrane participates in cell adhesion through three main methods:
  • Cell Adhesion Molecules (CAMs): Membrane proteins that anchor cells together, providing tissue cohesion.
  • Extracellular Matrix (ECM): A network of fibrous proteins in interstitial fluid that supports cellular trafficking and adhesion. Contains fibroblasts and is crucial in connective tissue.
    • Collagen: Offers tensile strength and tissue integrity, most abundant protein in the body.
    • Elastin: Provides elasticity and recoil properties.
    • Fibronectin: Functions as a biological glue, critical for cell positioning and adhesion, reduced levels associated with tumor metastasis.

Specialized Cell Junctions

• Desmosomes: Strong adherent junctions that anchor adjacent cells, most common in tissues needing flexibility and tensile strength, such as heart and skin.
• Tight Junctions: Seal adjacent cells to prevent leakage, found in epithelial tissues like the digestive tract; integrity loss linked to conditions like Crohn's disease and IBS.
• Gap Junctions: Facilitate communication by connecting cells with small tunnels, enhancing cellular coordination.

Cell Theory Principles

• Foundation of biological understanding, emphasizing that:
  • Cells are the basic structural and functional units of life in all organisms.
  • Cellular function is reliant on structure.
  • Cells across organisms share structural and functional similarities.

Quick Facts about Cells

• Human body comprises trillions of cells, classified into 200 cell types based on structure and function.
• Common cell features include plasma membrane, cytosol, and nucleus.

Main Structures and Functions of Cells

• Plasma Membrane: Acts as a barrier, controlling the movement of molecules.
• Nucleus: Houses genetic material (DNA).
• Endoplasmic Reticulum:
  • Rough ER: Synthesizes proteins.
  • Smooth ER: Involved in packaging.
• Golgi Complex: Modifies, packages, and distributes proteins.
• Lysosomes: Breakdown organic molecules using hydrolytic enzymes.
• Peroxisomes: Detoxify substances through oxidative enzymes.
• Centrioles: Organize microtubules for cell division and structure.
• Mitochondria: Powerhouse of the cell, responsible for ATP production through cellular respiration; characterized by a smooth outer membrane and folded inner membrane (cristae) for increased surface area.