Lipids Lecture 1

Inspirational Quote

• Carmen Gimenez (Poet, writer, editor): "Don't worry about what everybody else is doing. That's not only not going to get you anywhere, but it's also going to set you back."

Lipids Overview

Lipids - 1

Student Responsibilities

• Describe common characteristics of lipids.

• List nutritionally important lipid types.

• Explain implications of fatty acid structure on melting temperature.

• Name essential fatty acids and describe their sources and importance.

Introduction to Lipids

Characteristics of Lipids

• Insoluble in water: Hydrophobic nature.

• Amphipathic: Some have both hydrophilic and hydrophobic parts.

• Energy dense:

  • 1 g of fat provides 9.45 kcal.

  • Carbohydrates and protein provide 4.1 kcal/g.

• Structurally diverse: Compared to carbohydrates and proteins (which are polymers).

Functional Characteristics Related to Nutrition

• Energy dense: Primary energy supply in diet.

• Storage form of energy: Stored as fatty acids in adipose tissue.

• Absorption aid: Essential for the solubilization of lipid-soluble vitamins.

• Structural roles: Phospholipids in cell membranes.

• Signaling: Act as messengers and endocrine compounds in the body.

Classification of Lipids

• Structural Diversity: Lipids can be classified based on their structural components.

Glycerol-Based Lipids

Variety of Structures

• Structure includes:

  • Glycerol-based and non-glycerol based examples.

Glycerol vs Non-Glycerol Based Lipids

• Non-Glycerol Based Lipids include:

  • Cholesterol

  • Fatty acids

  • Steroids

  • Prostaglandins

  • Sphingomyelin/cerebrosides (nervous system lipids)

• Glycerol Based Lipids include:

  • Triglycerides (triacylglycerols)

  • Glycolipids

  • Phospholipids

Glycerol-Based Lipids Classifications

Simple vs Compound Lipids

• Simple Lipids:

  • Triglycerides: Composed of glycerol and three fatty acids.

• Compound Lipids:

  • Phospholipids and glycolipids:

    • Phospholipids: Glycerol, two fatty acids, and a phosphate group.

    • Glycolipids: Glycerol, two fatty acids, and a sugar (e.g., glucose or galactose).

Sources of Glycerolipids

Simple Glycerolipids

• Triglycerides: Found in oilseeds like:

  • Soybean

  • Cottonseed

  • Sunflower

  • Canola (rapeseed)

  • Peanut

Compound Glycerolipids

• Phospholipids: Present in cell membranes of animals and plants.

• Glycolipids: Found in plant cells as structural lipids.

Focus on Nutritional Lipids

Triglycerides and Fatty Acids

Characteristics of Fatty Acids

• Fatty acids are usually esterified (attached to something).

• Rarely found free; typically attached to:

  • Glycerol backbone (Triglyceride)

  • Phospholipid

  • Glycolipid.

Composition of Triglycerides

• Diversity:

  • Every triglyceride features a glycerol backbone.

  • Distinct carbon positions on glycerol.

  • Variable fatty acids in:

    • Chain length

    • Unsaturation.

Fatty Acid Structure

• General Structure: Carboxylic acid group and aliphatic chain lacking oxygen.

Chain Length Variation in Fatty Acids

• Length can range from 2 to more than 20 carbons.

• General observation: Even numbers of carbons in plants and animals.

• Examples:

  • Acetic acid (C2H4O2): 2 carbons

  • Eicosanoic acid (C20H40O2): 20 carbons.

Saturation Variation in Fatty Acids

• Saturation Measure: Based on the number of double bonds.

  • Saturated fatty acid: No double bonds.

  • Monounsaturated fatty acid: One double bond.

  • Polyunsaturated fatty acid: Two or more double bonds.

Common Fatty Acids

• 16 Carbon Palmitic Acid: Saturated

• 18 Carbon Stearic Acid: Saturated

• 18 Carbon Oleic Acid: Monounsaturated

• 18 Carbon Linoleic Acid: Polyunsaturated

Double Bond Geometry in Fatty Acids

Cis vs Trans Double Bonds

• Cis configuration: Hydrogens on the same side of the chain.

• Trans configuration: Hydrogens on opposite sides of the chain.

Implications of Double Bond Geometry

• Affects the shape and conformation of fatty acid chains:

  • Cis geometry: Produces an angle in fatty acid.

  • Trans geometry: Maintains linear orientation.

Melting Point of Fatty Acids

• Melting point defines transition temperature between solid and liquid forms of fatty acids or triglycerides.

• Determinants:

  • Longer chain length → higher melting temperature.

  • More saturation (fewer double bonds) → higher melting temperature.

  • Polyunsaturated fatty acids → remain liquid (oils) at room temperature.

Melting Point Examples

Saturated Fatty Acids

Unsaturated Fatty Acids

Essential Fatty Acids

Double Bonds and Geometry

• Cis vs Trans: Double bond positions along the chain refer to omega configurations:

  • Omega-6: First double bond at the 6th carbon from the methyl end.

  • Omega-3: First double bond at the 3rd carbon from the methyl end.

Importance of Essential Fatty Acids

• Essentials: Two fatty acids required in diet:

  • Linoleic acid: 18 carbons, omega-6, 2 double bonds (C18:2).

  • Linolenic acid: 18 carbons, omega-3, 3 double bonds (C18:3).

Why are these Fatty Acids Essential?

• Animals can only add double bonds up to position 9.

• Essential fatty acids contain double bonds between carbon 9 and the methyl end.

Uses of Essential Fatty Acids

• Found in cell membranes; contribute to phospholipids.

• Metabolism: Can be prolonged and desaturated.

• Linoleic Acid -> Can convert to Arachidonic Acid (C20:4).

• Precursor for lipid molecules such as prostaglandins, thromboxanes, and leukotrienes (which have roles in blood clotting, luteolysis, immune functions).

• Linolenic Acid -> Can convert to Eicosapentaenoic Acid (EPA, C20:5) and Docosahexaenoic Acid (DHA, C22:6), crucial for nervous system lipids.