[CH10] L10.0 [BCHM 2023] Lipids [FFAs] (Part-1)

Introduction to Lipids

  • Presented by Dr. Michael Weibel during Fundamentals of Biochemistry

  • Focus on the last macromolecule: lipids

What is a Lipid?

  • Definition varies by context:

    • Commonly referred to as fats (colloquial)

    • Biochemists define lipids as biologically relevant macromolecules

    • Main categories: free fatty acids, triacylglycerides, cholesterol (steroid derivatives)

    • Organic chemists broaden the definition, includes hydrocarbons, waxes, oils

  • Physical characteristics:

    • Hydrophobic nature is a common trait among all lipids

    • Not all characteristics are agreed upon (unlike proteins, nucleic acids, etc.)

Characteristics of Lipids

  • Hydrophobic: Most lipids are primarily hydrophobic, though some may be amphiphilic (having both hydrophobic and hydrophilic parts)

  • Transition point: Understanding the solid to liquid transition (melt point) is key to categorizing and studying lipids

  • Most lipids do not have a defined monomer—their classification is based on physical characteristics instead of discrete building blocks

Functions of Lipids

  • Structural: Forming cell membranes (lipid bilayer) with:

    • Phospholipids

    • Sphingolipids

    • Glycolipids

  • Signaling: Serve as signaling molecules including hormones (e.g., glucocorticoids, e.g., cortisol, aldosterone)

  • Nutritional: Fat-soluble vitamins (A, D, E, K)

  • Energy Storage: Lipids provide a long-term energy source and are stored as triacylglycerides

Categories of Lipids

  • Energy-related:

    • Free fatty acids: Simple carboxylic acids with long hydrocarbon chains (oxidized for energy)

  • Triacylglycerides (TAGs): Glycerol backbone with three free fatty acids; main form of stored fat in the body

  • Membrane-related lipids: Include phospholipids for the lipid bilayer

  • Steroids: Influence membrane fluidity; include cholesterol derivatives

Free Fatty Acids (FFAs)

  • Defined as carboxylic acids with long hydrocarbon chains

  • Usually even-numbered, with mostly 12-24 carbons being most common in the body

    • Rarely odd-numbered, making odd-numbered FFAs less important in biochemistry

  • Function as energy precursors—highly reduced and non-polar (do not need water)

  • Classified into:

    • Saturated: No double bonds

    • Unsaturated: One or more double bonds categorized as:

      • Monounsaturated (MUFAs): One double bond

      • Polyunsaturated (PUFAs): Multiple double bonds

Nomenclature of Free Fatty Acids

  1. Trivial Name: Most common name recognized (e.g., oleic acid as the main fat in olive oil)

  2. Lipid Number:

    • Format: #Carbons : #Double Bonds (Example: Oleic acid = 18:1)

    • Specific double bond position can be included (e.g., 18:1(9))

  3. Greek Letter Nomenclature: Each carbon adjacent to functional groups is named (e.g. Alpha, Beta)

  4. Omega Nomenclature: Counts from the tail end of the fatty acid (e.g., Omega-3, Omega-6)

  5. Delta Nomenclature: Refers specifically to the positions of double bonds (e.g. Delta-9 for oleic acid)

Importance of Understanding Lipid Chemistry

  • Lipids are involved in crucial biological processes, signaling, and energy storage

  • Identifying lipid functions and their physical characteristics aids in understanding metabolic processes and health issues (e.g., obesity)

  • Research potential exists, particularly in areas like free fatty acid receptors and their role in metabolism

Conclusion

  • Lipids play diverse roles in biology as structural components, signaling molecules, and energy storage sources.

  • The complexity and variability of lipid classification highlight the importance of physical characteristics over defined structural monomers.