Lecture on Lipids, Cell Membranes, and Transport

What are Lipids?

• Definition: Group of compounds with little to no affinity for water (hydrophobic).
• Cause of Hydrophobia: Non-polar nature of carbon to hydrogen bonds in fatty acids.
• Types of Lipids: Fats, phospholipids, and steroids.

Types of Lipids

Fats

• Function: Energy storage.
• Structure: Glycerol molecule attached to fatty acid chain.
• Fatty Acid Chain: Non-polar, hydrophobic; breaks to synthesize ATP.
• Saturated Fats: Solid at room temperature; no double bonds.
• Unsaturated Fats: Liquid at room temperature; have one or more double bonds.
• Trans Fats: Different orientation of molecules; considered bad fats.

Phospholipids

• Structure: Two fatty acid tails with a phosphate group.
• Properties: Hydrophobic tails, hydrophilic heads.
• In Water: Form micelles or liposomes.
• Lipid Bilayer: Structure of cell membranes.

Steroids

• Structure: Carbon skeleton with four rings.
• Examples: Cholesterol, estrogen, testosterone.

Cell Membranes

• Composition: Lipid bilayer with embedded proteins.
• Function: Selectively permeable (some materials can enter freely, others require energy).

Types of Transport

Passive Transport

• Diffusion: Molecules move from high to low concentration.
• Facilitated Diffusion: Uses transport proteins; no energy required.
• Osmosis: Diffusion of water across a membrane.

Active Transport

• Requires Energy (ATP): Moves substances against concentration gradient.
• Examples: Sodium-potassium pump, co-transport.

Membrane Transport Processes

• Exocytosis: Expulsion of substances from cell.
• Endocytosis: Intake of materials into cell.
• Pinocytosis: Non-specific intake of solutes.
• Receptor-mediated Endocytosis: Specific chemical intake.

Origin of Cells

• Timeline: First cells appeared 4.0 to 4.3 billion years ago.
• Theories: Cells originated from meteorites, deep-sea vents, or lightning.
• RNA Hypothesis: First self-replicating molecule assumed to be RNA.
• Cell Theory: Cells are basic units of life; cannot exist without membranes.
• Formation of Membranes: Phospholipids form bilayers spontaneously.