Biochem Lab M2

Lipids

Chemically heterogeneous family of biomolecules; not defined by one functional group; insoluble in polar solvents but soluble in nonpolar solvents; contain many C–C and C–H bonds, leading to poor water solubility

Hydrolyzable Lipids

Lipids that can be converted into smaller molecules by hydrolysis

Nonhydrolyzable Lipids

Lipids that cannot be cleaved into smaller molecules by hydrolysis

Fatty Acids

Hydrolyzable lipids derived from fatty acids; consist of a hydrocarbon chain and a carboxyl group (–COOH)

Saturated Fatty Acids

Hydrocarbon chains with only single bonds; usually solid at room temperature; often from animal sources

Unsaturated Fatty Acids

Hydrocarbon chains with one or more double bonds; usually liquid at room temperature; often from plant sources

Waxes

Esters of saturated fatty acids and high molecular weight monohydric alcohols; hydrophobic, form protective coats in plants and animals

Beeswax

Wax produced by honey bees (Apis mellifera)

Lanolin

Wax obtained from sheep (Ovis aries)

Carnauba Wax

Wax from the carnauba palm (Copernicia prunifera)

Spermaceti

Wax from the head of the sperm whale (Physeter macrocephalus)

Jojoba Wax

Plant-derived wax (Simmondsia chinensis), substitute for spermaceti.

Triacylglycerol (TAG)

Also called triglycerides; esters derived from glycerol and fatty acids

Saturated TAG

Triacylglycerol composed of only saturated fatty acids (no double bonds)

Monounsaturated TAG

Triacylglycerol composed of one unsaturated fatty acid

Polyunsaturated TAG

Triacylglycerol composed of more than one unsaturated fatty acid

Fats

Triacylglycerols solid at room temperature; more saturated fatty acids; usually from animal sources

Fixed Oils

Triacylglycerols liquid at room temperature; more unsaturated fatty acids; usually from plant sources

Phospholipids (Phosphoacylglycerols)

Esters of glycerol, fatty acids, and a phosphorylated alcohol; third fatty acid replaced with a phosphodiester group

Phosphatidyl Choline (Lecithin)

Major phosphoglycerol in cell membranes; polar head group is choline

Phosphatidyl Serine

Phosphoglyceride with serine as polar head group

Phosphatidyl Inositol

Precursor for secondary messenger synthesis; polar head group is inositol

Phosphatidyl Glycerol (Cardiolipin)

Phosphoglyceride with glycerol as polar head group

Phosphatidyl Ethanolamine (Cephalin)

Phosphoglyceride with ethanolamine as polar head group

Sphingolipids

Lipids with sphingosine backbone and fatty acid (amide linkage) plus a polar head group

Ceramide

Parent compound of sphingolipids; amide of sphingosine and fatty acid

Sphingomyelin

Sphingolipid with phosphocholine or phosphoethanolamine as polar head group; component of myelin sheath

Cerebrosides

Sphingolipids with monosaccharide (glucose or galactose) as polar head group

Globosides

Sphingolipids with disaccharide or neutral oligosaccharide head group

Gangliosides

Sphingolipids with charged oligosaccharide head groups

Steroids

Nonhydrolyzable lipids; have a four

Cholesterol

Sterol in animals; provides membrane rigidity and fluidity; precursor for steroid/sex hormone synthesis; most abundant steroid in the body

Sitosterol/Stigmasterol

Plant sterols

Ergosterol

Fungal sterol

Fat

Soluble Vitamins

Vitamin A (Retinal)

Antioxidant

Vitamin D (Cholecalciferol)

Important for Ca absorption

Vitamin E (α-Tocopherol)

Antioxidant and prevents lipid peroxidation

Vitamin K (Phytonadione)

Anti-coagulant

Eicosanoids

Potent compounds derived from arachidonic acid; not stored, synthesized in response to stimuli

Prostaglandins

Lipids synthesized at tissue damage or infection sites; regulate inflammation, blood flow, clotting

Leukotrienes

Lipids derived from arachidonic acid; activate immune and inflammatory responses

Phosphate Test (Molybdate Test)

Detects phosphate in lipid hydrolysates; yellow color indicates presence; positive for phospholipids, negative for fats and cholesterol

Acrolein Test

Heating lipids with glycerol in presence of KHSO₄ produces acrolein with pungent odor; confirms presence of glycerol (fats or lecithin); differentiates lecithin from cholesterol

Liebermann-Burchard Test

Test for cholesterol using acetic anhydride and sulfuric acid; produces color change from pink to lilac to deep green due to –OH group and unsaturation in cholesterol.