Lipids Overview

Study Notes

Lipids are molecules produced by living organisms.
Major organic biomolecules include lipids, nucleic acids, carbohydrates, and proteins.
Minerals and vitamins are also considered biomolecules.
Structure and function of biomolecules are fundamentally related and influenced by environmental factors.
Lipids are a diverse group of organic compounds related to fatty acids.
Fats, oils, waxes, and other compounds are included in this group.
Lipids are oily and greasy, and are not soluble in water.
Polar solvents dissolve lipids.
The predominant ingredient in lipids is the hydrocarbon chain.
Lipids are not polymer structures made up of monomers.
Lipids make up 18-25% of an adult's body mass.
Lipids are primarily found in plasma, biological membranes, and adipose tissue.
Adipose tissue: loose connective tissue designed to store fat in adipocytes (fat cells) found under the skin, around the kidneys, and in the abdomen and breasts.
Adipose tissue functions: reserve fuel, insulation against heat loss, and support/protection of organs.

Lipids act as structural components of biological membranes and nerves.
They include glycolipids, phospholipids, sphingomyelins, cholesterol, and lipoproteins.
Lipids maintain membrane fluidity.
Lipids are a valuable energy reservoir.
Stored lipids are the chief form of energy in the body and are more palatable and storable compared to carbohydrates.
Lipid oxidation produces twice the energy produced from carbohydrates.
Lipids insulate the body from heat loss by acting as a thermal insulator in subcutaneous tissues.
Lipids act as a protective cushion for internal organs and are a protective coat for many organisms.
Lipids are involved in cell-cell adhesion, cell recognition, and tissue immunity (glycolipids).
Lipids such as bile acids and lecithins aid in the digestion and absorption of dietary fats.
Lipids act as crucial cellular metabolic regulators, modulators of intracellular messengers, and intracellular messengers (steroid hormones, prostaglandins, inositol triphosphate (IP3)).
Lipids provide the body with fat-soluble vitamins (A, D, E, and K) and essential fatty acids.
Lipids are components of the electron transport chain (ubiquinone: coenzyme Q).

Saponification Classification System: Based on a chemical reaction called saponification (lipid undergoes ester hydrolysis in a basic condition (KOH)).
- Saponifiable: triglycerides, waxes, phospholipids, glycolipids
- Non-saponifiable: steroids, terpenes, vitamins, eicosanoids
Bloor's Classification System: Based on the chemical composition of lipids.
- Simple lipids: fats and oils, waxes
- Compound lipids: phospholipids, glycolipids, lipoproteins, glycerophospholipids, sphingophospholipids, glyceroglycolipids, glycosphingolipids,
- Derived lipids: steroids, fatty acids, terpenes, carotenoids

FAs are aliphatic monocarboxylic organic acids.
FAs contain a hydrocarbon chain with one carboxylic group at one end.
FAs are amphipathic, possessing both hydrophilic (water-soluble) and hydrophobic (water-insoluble) regions.
They have a carboxyl group (-COOH) and a hydrocarbon chain (R group).
More than 100 different FAs occur naturally.
Most FAs occur as esters (not free).
Most FAs are commonly synthesized from the condensation of 2-carbon units (acetate).
In most biological systems, FAs have an even number of carbon atoms (4-36); odd numbers occur less frequently.
FAs are typically straight and unbranched, but some have branched or heterocyclic chains.
They are classified as short, medium, or long chain depending on the number of carbon atoms in their hydrocarbon chain.
Saturated FAs: have no double bonds within their hydrocarbon chains.
Unsaturated FAs: contain one or more double bonds within their hydrocarbon chains.
The presence or absence of double bonds determines the degree of saturation.
Nomenclature: Fatty acids can be numbered from the carboxyl end or methyl end.

Short-chain FAs (≤10 carbons) are water-soluble and volatile.
Long-chain FAs (>10 carbons) are water-insoluble, non-volatile, and solid at room temperature.
Saturated FAs are common in animals and plants.
Examples of saturated FAs include palmitic acid (16:0) and stearic acid (18:0).
Longer chains result in higher melting points.
The higher melting point is a result of the increased energy required to disrupt hydrophobic interactions between saturated fatty acid molecules.
Saturated FA sources include butter, cheese, chocolate, coconut, egg yolk, lard, meat, milk, palm oil, poultry, vegetable shortening, margarine, and salad dressings.