part 4- Lipids

Introduction to Lipids

• Lipids are a category of macromolecules.

• Common forms found in nutrition labels: fats and cholesterol.

• Everyday examples: oils and butter, as well as visible fats in foods like steak.

Functions of Lipids

• Energy Source: Lipids serve as a calorically dense source of energy for the body.

• Signaling Molecules: Steroids act as hormones, examples include testosterone and cortisol.

• Cell Membrane Structure: Phospholipids are integral components of cell membranes, forming the outer boundary of cells.

Lipid Structures

• Triglycerides: Composed of 3 fatty acid tails linked to a glycerol carbohydrate.

  • Fats (solid at room temperature) vs oils (liquid at room temperature).

• Steroids: Structure consists of 4 carbon rings; they play a role in signaling.

  • Crucial for hormone production, examples include testosterone and cortisol.

• Phospholipids: Similar to triglycerides but have 2 fatty acid tails and a polar hydrophilic group

  • Essential for forming cell membranes due to their amphipathic nature.

Fatty Acids

• Structure: Chains of carbons flanked by hydrogen, with a carboxyl group at one end.

• Classification: Based on carbon chain length and presence of double bonds.

  • Saturated Fatty Acids: No double bonds; carbon atoms are fully saturated with hydrogen. Example: Stearic acid.

  • Unsaturated Fatty Acids: Contain one or more double bonds which leads to fewer hydrogen atoms. Example: Oleic acid.

Saturated vs Unsaturated Fats

• Saturated Fats: Typically solid at room temperature, seen in animal sources (butter, steak).

• Unsaturated Fats: Usually liquid at room temperature; derived from plants (olive oil, canola oil).

• Industrial processes can modify unsaturated fats to create trans fats, which may behave like saturated fats (e.g., margarine).

Lipid Partnerships in Metabolism

• Lipids vs Carbohydrates:

  • Lipids provide long-term energy storage.

  • Carbohydrates are suitable for short-term energy storage.

Steroids and Hormones

• Derived from cholesterol, essential for producing hormones like:

  • Cortisol: Stress hormone.

  • Testosterone: Promotes certain bodily functions like muscle growth.

  • Vitamin D: Synthesized in response to sun exposure.

Phospholipids: The Building Blocks of Cell Membranes

• Amphipathic Nature: One end is hydrophilic (polar group) while the other is hydrophobic (fatty acid tails).

• Formation of Micelles: Aggregation in water to shield hydrophobic parts.

• Liposomes: Resulting spherical structures formed by phospholipids in water; considered precursors for cellular structure.

Cell Membrane Properties

• Fluid Mosaic Model: Describes the cell membrane as a fluid structure composed of phospholipids and embedded proteins.

• Selective Permeability:

  • Small nonpolar molecules can easily pass through (e.g., oxygen, carbon dioxide).

  • Slightly larger molecules (e.g., water, glycerol) may pass with assistance.

  • Large and polar molecules (e.g., glucose, sucrose) require specific protein channels for transport.

Protein Functions in Membranes

• Role of Membrane Proteins: Facilitate transport across the membrane.

  • Can be channels allowing passive movement or active transport that requires energy.

• Channel Proteins: Allow passage of larger/charged molecules through the membrane.

• Fluid Nature: Membranes are dynamic, allowing for movement of proteins and lipids, maintaining cellular functionality.

Conclusion

• Lipids encompass various forms including triglycerides (fats/oils), steroids (signaling agents), and phospholipids (membrane structure).

• Their unique structures and properties are essential for energy storage, cellular signaling, and the formation of cellular boundaries.