Lipids: Structure, Nomenclature, and Biological Functions

Vocabulary practice flashcards covering lipid classification, fatty acid structure and nomenclature, storage fats, glycerophospholipids, sphingolipids, sterols, and signaling lipids based on Lehninger Principles of Biochemistry.

Lipids

A diverse class of biological molecules whose defining feature is insolubility in water; they possess amphipathic structures and do not form polymers.

Amphipathic Lipid Molecule

A molecule characterized by having both a hydrophilic polar head group that interacts with water and a hydrophobic nonpolar tail.

Fatty Acids

Carboxylic acids possessing a hydrocarbon tail, typically containing an even number of carbon atoms (4 to 36, commonly 12 to 24), which are mostly unbranched with double bonds almost exclusively in the cis configuration.

Saturated Fatty Acid

A fatty acid with no double bonds between carbon atoms along its hydrocarbon chain, allowing it to pack orderly with extensive nonpolar interactions.

Polyunsaturated Fatty Acid

A fatty acid that contains two or more carbon-carbon double bonds in its alkyl chain, where each double bond is separated from the next by an alkyl group.

Delta ($\Delta$) Numbering System

A fatty acid nomenclature system specifying the total carbon count, number of double bonds, and superscript numbers designating the first carbon of each double bond relative to the carbonyl carbon (carbon 1).

Omega ($\omega$) Numbering System

A fatty acid nomenclature method that describes the position of the first double bond numbered relative to the terminal methyl carbon.

Essential Fatty Acids

Fatty acids that humans cannot synthesize because human enzymes cannot introduce cis double bonds beyond $C_9$, specifically linoleic acid ($18:2(\Delta^{9,12})$) and alpha-linolenic acid ($18:3(\Delta^{9,12,15})$).

Waxes

Water-insoluble, high-melting-point esters formed from the condensation of a long-chain saturated or unsaturated fatty acid with a long-chain alcohol.

Triacylglycerols

Nonpolar storage lipids composed of three fatty acids joined in ester linkage to a single glycerol molecule.

L-Glycerol 3-phosphate

The chiral, phosphorylated three-carbon intermediate onto which fatty acids are esterified at hydroxyl groups 1 and 2 to assemble glycerophospholipids.

Glycerophospholipids

The primary structural lipid constituents of cell membranes, composed of two fatty acids esterified to carbons 1 and 2 of L-glycerol 3-phosphate and a polar alcohol head group esterified to the phosphate.

Phosphatidylcholine

The predominant glycerophospholipid found in the outer leaflet of most eukaryotic cell membranes, consisting of a phosphocholine polar head group attached to diacylglycerol.

Sphingosine

A long-chain amino alcohol that forms the structural backbone of sphingolipids rather than glycerol.

Ceramide

The fundamental structural unit of all sphingolipids, formed by joining a fatty acid to the amino group of sphingosine via an amide linkage.

Sphingomyelin

A subclass of sphingolipids consisting of ceramide joined to phosphocholine or phosphoethanolamine; it is an abundant structural component of the myelin sheath surrounding nerve cells.

Cerebrosides

Neutral glycosphingolipids consisting of a ceramide unit linked to a single monosaccharide, commonly galactose in neural tissue and glucose in non-neural tissue.

Globosides

Neutral glycosphingolipids containing a ceramide backbone linked to two or more neutral sugar units (di-, tri-, or tetrasaccharides).

Gangliosides

Complex, negatively charged glycosphingolipids containing oligosaccharide head groups terminating in one or more sialic acid residues, essential for cellular recognition.

ABO Blood Group Antigens

Cell surface antigens determined by specific oligosaccharide head groups on glycosphingolipids, where type A carries an added $N$-acetylgalactosamine, type B carries an added galactose, and type O lacks an active glycosyltransferase.

Cyclopentanoperhydrophenanthrene

The rigid, four-fused-ring steroid nucleus consisting of three six-carbon rings (A, B, C) and one five-carbon ring (D) found in sterols and steroid hormones.

Cholesterol

A major sterol found in animal cell membranes consisting of a cyclopentanoperhydrophenanthrene core, a $C_3$ hydroxyl head group, and an alkyl side chain, functioning to modulate membrane permeability and fluidity.

Steroid Hormones

Oxidized, endocrine-signaling derivatives of sterols that retain the four-ring core but lack the alkyl side chain, rendering them more polar than cholesterol.

Calcitriol (1$\alpha$,25-Dihydroxyvitamin $D_3$)

The active hormone form of vitamin $D_3$ synthesized through UV-dependent photolysis in skin followed by enzymatic hydroxylations in the liver and kidney to regulate intestinal calcium absorption.

Prostaglandins

Paracrine eicosanoid signaling molecules containing a five-membered cyclopentane ring synthesized from arachidonic acid that mediate inflammation, fever, blood flow, and smooth muscle contraction.

Thromboxanes

Signaling eicosanoids derived from arachidonic acid containing a six-membered ether ring that stimulate platelet aggregation and blood clot formation.

Leukotrienes

Linear signaling lipids synthesized enzymatically from arachidonic acid that trigger powerful smooth muscle contraction in lung tissue.

Vitamin E

A lipid-soluble antioxidant containing a substituted aromatic ring and long isoprenoid chain that destroys reactive oxygen free radicals to protect membrane lipids from oxidative damage.

Vitamin K

A lipid cofactor containing an aromatic ring and an isoprenoid side chain essential for the activation of prothrombin in the blood clotting cascade.

Warfarin

A synthetic blood anticoagulant compound that functions as a competitive inhibitor of vitamin K-dependent blood clotting pathways.

18:2Δ9,12

Linoleic Acid

18:3Δ9,12,15

Alpha-Linolenic Acid

decreases

solubility of lipids ____ as length of hydrocarbon chain increases

decreases

melting point of lipids ______ as number of double bonds increases

decreases

melting point of lipids _______ as chain length decreases

lower

unsaturated cis fatty acids have _____ melting point than saturated fatty acids

16:1(Δ9)

Palmitoleic acid

18:1(Δ9)

Oleic acid

20:4(Δ5,8,11,14)

Arachidonic acid

A blood type

N-acetylgalactosamine

B blood type

transfers a galactose

O blood type

no active glycosyltransferase

sphingolipids

ceramide joined to a polar group, amino alcohol