Biological Functions of Lipids

Study Notes

Energy Source: Lipids provide 9kcal of energy per gram, which is more than carbohydrates or proteins.
Energy Storage: Triglycerides are stored in adipocytes (fat cells) for long-term energy reserves.
Structural Component of Cell Membranes: Phosphoglycerides, steroids, and sphingolipids are essential components of cell membranes.
Hormones: Steroids are vital intercellular messengers regulating various bodily functions.
Lipid-Soluble Vitamins: Vitamins A, E, D, and K are fat-soluble and require dietary fat for absorption.
Shock Absorption and Insulation: Lipids provide cushioning and insulation for organs and the body.

Fatty Acids: These are the building blocks of many lipids.
- Saturated Fatty Acids: Have no double bonds between carbon atoms.
- Unsaturated Fatty Acids: Have one or more double bonds between carbon atoms.
Glycerides: Composed of glycerol and fatty acids.
Nonglyceride Lipids: This category includes:
- Sphingolipids: Essential for cell membrane structure.
- Steroids: A class of compounds including cholesterol and hormones.
- Waxes: Provide protective coatings for plants and animals.

Structure: Unbranched, long, straight chains of an even number of carbon atoms with a carboxyl group (COOH).
Length: Most common chains range from 10 to 20 carbons.
Stearic Acid: A typical saturated fatty acid with 18 carbons.
Oleic Acid: A typical unsaturated fatty acid with 18 carbons.

Saturated Fatty Acids: Have no double bonds between carbon atoms, resulting in more rigid structures that pack tightly.
Unsaturated Fatty Acids: Have one or more double bonds between carbon atoms, resulting in less rigid structures that pack loosely.
Cis configuration: In unsaturated fats, the presence of a double bond prevents tight packing, leading to lower melting temperatures.

Double bonds: The first double bond is typically at the ninth carbon atom.
Cis configuration: The double bonds are usually in the cis configuration, which causes a bend in the fatty acid chain.

Melting Point: Increases with increasing carbon number.
Melting Point Comparison: Saturated fatty acids have higher melting points than unsaturated fatty acids with the same number of carbons.
Packing: Saturated fatty acids pack tightly due to the straight structure, while cis double bonds in unsaturated fatty acids prevent tight packing.
Double Bonds Effect: Double bonds decrease melting point relative to saturated fatty acids.

Esterification: A reaction between a fatty acid and an alcohol, resulting in the formation of an ester and water.

Acid Hydrolysis: The reverse of esterification, breaking down esters into fatty acids and alcohols.

Saponification: Base-catalyzed hydrolysis of an ester, producing:
- An alcohol.
- An ionized salt (soap).

Soaps: Soaps have a long, uncharged hydrocarbon tail and a negatively charged carboxylate group at the end.
Micelles: Soaps form micelles in water, encasing oil and dirt particles for removal.

Hydrogenation: A chemical reaction that converts unsaturated fatty acids to saturated fatty acids by adding hydrogen.
Food Industry: Hydrogenation is used to convert liquid vegetable oils into solids.
Margarine: A common example of a hydrogenated fat.

Essential Fatty Acids: Cannot be synthesized by the body and must be obtained from the diet.
- Linoleic Acid: An essential fatty acid needed to synthesize arachidonic acid.
Arachidonic Acid: A 20-carbon unsaturated fatty acid that serves as the precursor for eicosanoids.
Eicosanoids: A group of structurally similar compounds, including:
- Prostaglandins: Potent biological molecules involved in inflammation and pain.
- Leukotrienes: Involved in allergic and inflammatory responses.
- Thromboxanes: Play a role in blood clotting.

Production: Produced in most tissues, acting as "local hormones."
Structure: Derived from 20-carbon unsaturated fatty acids and contain a 5-carbon ring.
Effects: Exert their effects on nearby cells.