BIOC*2580 - 1

Course Transition

  • Acknowledgment of midterm results.

  • Structure shift for the second half of the course:

    • Transition from discussing proteins to other biomolecules, mainly lipids.

Lipids Overview

  • Definition of Lipids:

    • Diverse group of molecules.

    • Not defined by structure but by chemical properties, primarily hydrophobicity.

  • Comparison to Proteins:

    • Proteins defined by specific structural motifs (e.g., amino acids).

    • Lipids defined by hydrophobic nature, requiring nonpolar solvents for dissolution (e.g., chloroform and methanol mixture).

Major Functions of Lipids

  • Primary functions include:

    • Energy storage:

      • Triacylglycerols (triglycerides) are main energy storage form in organisms.

    • Formation of biological membranes:

      • Lipids involved: phospholipids and sterols.

    • Additional roles in metabolism: signal transduction, enzyme cofactors, etc.

Types of Lipids to be Discussed

  1. Fatty Acids:

    • Building blocks for complex lipids.

  2. Triacylglycerols:

    • Storage form of fats and oils.

  3. Phosphoglycerides:

    • Major components of cell membranes.

Fatty Acids

  • Structure:

    • Composed of carboxylic acid (COOH) and a hydrocarbon chain (length varies from 4 to 36 carbons).

  • Types based on saturation:

    • Saturated: no double bonds.

    • Unsaturated: one or more double bonds.

    • Monounsaturated: one double bond.

    • Polyunsaturated: multiple double bonds.

  • Numbering System:

    • Carbon atoms labeled starting from carboxylic carbon (beta, alpha, and omega carbons identified).

Properties of Fatty Acids

  • Reactivity:

    • Carboxylic acid group is reactive; hydrocarbon chain is nonreactive.

  • Double Bond Configurations:

    • Cis (bent structure) vs. Trans (linear structure) configuration:

    • Cis introduces kinks; Trans aligns in straight configuration affecting physical properties.

    • Methylene-bridged pattern for polyunsaturated fatty acids.

Common Features of Fatty Acids

  • Majority have even number of carbons (rare odd numbered ones).

  • Typically straight chains without branches.

  • Cis vs. Trans Configuration:

    • Most naturally occurring fatty acids are in cis form, affecting their melting points and structures.'

Common Fatty Acids (Saturated)

Let My Pal Stay Arounds

  • Laurate (C12:0) - a melting point of about 44°C, commonly found in palm kernel oil and coconut oil. bay, laurel

  • Myristate (C14:0) - a melting point of approximately 54°C, prevalent in dairy products and found in nut oils, contributing to their creamy texture. myrtle, nutmeg

  • Palmitate (C16:0) - a melting point of around 63°C, commonly found in palm oil and animal fats, and plays a significant role in the structure of cell membranes. palm

  • Stearate (C18:0) - a melting point of about 69°C, found in various animal fats and vegetable oils, and is important for energy storage and metabolic processes. tallow

  • Arachidate(C20:0) - A saturated fatty acid with a melting point of approximately 76°C, primarily found in some animal fats and certain vegetable oils, and is involved in cellular signaling and membrane stability. peanut

Naming Fatty Acids

  • Nomenclature:

    • First number indicates total carbon atoms.

    • Colon separates number of double bonds.

    • Superscripts indicate position of the double bonds from the carboxylic carbon (delta system).

    • Omega system identifies first double bond from the methyl carbon.

Physical Properties of Fatty Acids

  • Melting Point and Solubility

    • Saturated fatty acids have higher melting points due to tight packing.

    • Unsaturated fatty acids (cis) have lower melting points due to kinks leading to less packing.

    • Trans fatty acids behave more like saturated due to linear structure from trans double bonds.

    • The longer the chain the higher the melting point, the lower the solubility

Derivatives of Fatty Acids

  • Carboxylic acids can combine with alcohols to form esters.

  • Carboxylic acids can combine with acids to form acid anhydrides.

Triglycerides (Triacylglycerols) (TAGs; Fats and Oils)

  • Formation:

    • Composed of glycerol and three fatty acids (ester bonds formed through reactions of carboxyl groups with alcohols).

  • Properties:

    • Fatty acids not found free; instead, found in triglycerides.

    • Triglycerides are HIGHLY hydrophobic (polar caboxilic acids are tied as esters)

    • They come as mixed triglycerides (different fatty acids) vs. simple triglycerides (same fatty acids).

    • Melting point is dependent on length and degree of saturation of fatty acid constituents

  • Source of Energy:

    • Commonly stored in the body as triacylglycerols, providing energy.

Physical State of Triglycerides

  • At room temperature:

    • Fats (solid)

    • Oils (liquid)

  • Solid fats usually higher in saturated fats, while oils have higher unsaturated fats.

  • Examples from Nature:

    • Olive oil, butter, beef fat vary in composition affecting states and melting points.

Conclusion

  • Triglycerides form the bulk of dietary fats and energy storage molecules.

    • Importance of understanding complex lipids for broader biochemical studies in metabolism and cell structure.