Lipids - Chapter 19 Lecture Review

Flashcards covering the classification, structure, physical properties, and biological functions of lipids, including fatty acids, triacylglycerols, membrane lipids, steroids, and eicosanoids, and waxes.

Lipid

An organic compound found in living organisms that is insoluble (or only sparingly soluble) in water but soluble in non-polar organic solvents.

Triacylglycerols

The most widespread energy-storage lipids in the body, primarily concentrated in specialized cells called adipocytes.

Fatty acid

Naturally occurring monocarboxylic acids with a linear (unbranched) carbon chain.

Saturated fatty acid

A fatty acid in which all carbon-carbon bonds are single bonds.

Monounsaturated fatty acid

A fatty acid with a carbon chain in which one carbon–carbon double bond is present.

Polyunsaturated fatty acid (PUFA)

A fatty acid with a carbon chain in which two or more carbon–carbon double bonds are present; up to six double bonds can be found in important PUFAs.

Omega ($\omega$)-3 fatty acid

An unsaturated fatty acid with its endmost double bond three carbon atoms away from its methyl end.

Omega ($\omega$)-6 fatty acid

An unsaturated fatty acid with its endmost double bond six carbon atoms away from its methyl end.

Essential fatty acid

A fatty acid that must be obtained from dietary sources because it is not synthesized within the body, such as linoleic and linolenic acids.

Simple Triacylglycerol

A triester formed from the esterification of glycerol with three identical fatty acids.

Mixed Triacylglycerol

A triester formed from the esterification of glycerol with more than one kind of fatty acid; these are the most common types found in nature.

Saponification

The hydrolysis of a triacylglycerol in a basic solution (e.g., $NaOH$) to produce a salt of a fatty acid (soap) and glycerol.

Hydrogenation

The chemical process of adding hydrogen across double bonds ($C=C$) in a lipid, which increases the degree of saturation and can turn liquid oils into semi-solid fats.

Phospholipid

A membrane lipid that contains one or more fatty acids, a phosphate group, a platform molecule (glycerol or sphingosine), and an alcohol.

Glycerophospholipid

A membrane lipid containing two fatty acids and a phosphate group esterified to a glycerol molecule, with an alcohol esterified to the phosphate group.

Sphingophospholipid

A membrane lipid based on the 18-carbon monounsaturated aminodialcohol sphingosine, containing one fatty acid, one phosphate group, and an alcohol.

Sphingomyelin

Specific sphingophospholipids in which the alcohol esterified to the phosphate group is choline; they are structural components of the myelin sheath of neurons.

Sphingoglycolipid

A membrane lipid that contains both a fatty acid and a carbohydrate (glucose or galactose) attached to a sphingosine molecule.

Cerebroside

The simplest sphingoglycolipids, which contain a single monosaccharide unit and occur primarily in the brain.

Ganglioside

Complex sphingoglycolipids that contain a branched chain of up to seven monosaccharide residues; they occur in the brain's gray matter and myelin sheath.

Steroid

A lipid whose structure is based on a fused ring system of three 6-carbon rings and one 5-carbon ring.

Cholesterol

A $C_{27}$ steroid molecule that is a major component of cell membranes, serves as a precursor for other steroids, and acts as a membrane plasticizer.

Lipid Bilayer

A two-layer structure of phospholipids that surrounds cells, with nonpolar tails in the middle and polar heads on the surface, measuring approximately $6-9 \times 10^{-9} \text{ m}$ thick.

Passive transport

The movement of a substance across a cell membrane by diffusion from a region of higher concentration to a region of lower concentration without the expenditure of energy.

Facilitated transport

The movement of a substance across a cell membrane from higher to lower concentration with the aid of a specific membrane protein.

Active transport

The movement of a substance across a cell membrane against a concentration gradient with the aid of membrane proteins (pumps) and cellular energy (ATP).

Bile acid

A cholesterol derivative that functions as an emulsifying agent to make dietary lipids soluble in the aqueous environment of the digestive tract.

Hormone

A biochemical substance produced by a ductless gland that serves as a chemical messenger or means of communication between various tissues.

Eicosanoid

A messenger lipid derived from arachidonic acid ($20:4$) that exerts physiological effects (such as inflammation, pain, or blood clotting) in the tissues where it is synthesized.

Prostaglandin

A type of eicosanoid that contains a cyclopentane ring and is involved in raising body temperature, intensifying pain, and inflammatory responses.

Thromboxane

A type of eicosanoid derivative that contains a cyclic ether ring and functions to promote platelet aggregation.

Leukotriene

A type of eicosanoid derivative containing three conjugated double bonds that promotes inflammatory and hypersensitivity (allergy) responses.

Biological wax

A protective-coating lipid formed by the monoesterification of a long-chain fatty acid ($C_{14}$ to $C_{36}$) and a long-chain alcohol ($C_{16}$ to $C_{30}$).