LIPIDS

Membrane lipids are components of cell membranes, including phospholipids, sphingoglycolipids, and cholesterol.

Current recommendations advise limiting total fat intake to 30% of total calories, with up to 15% from monounsaturated fats, up to 10% from polyunsaturated fats, and less than 10% from saturated fats.

Glycerophospholipids undergo hydrolysis and saponification reactions like triacylglycerols.

Energy-storage lipids, such as fats and oils, store energy in adipose tissue. The primary distinction is their physical state at room temperature; fats are solid or semi-solid, while oils are liquid.

Coconut oil is a notable exception as it is highly saturated but remains liquid due to its rich content of shorter-chain fatty acids, particularly lauric acid.

Saponification is the alkaline hydrolysis of fats, involving two steps: hydrolysis and acid-base reaction, resulting in glycerol and fatty acid salts (soaps).

LDLs (low-density lipoproteins) carry cholesterol from the liver to tissues, while HDLs (high-density lipoproteins) carry excess cholesterol from tissues back to the liver.

Bile contains emulsifying agents secreted by the liver, bile pigments, cholesterol, and electrolytes such as bicarbonate ions. Glucocorticoids regulate glucose metabolism and counteract inflammation.

Prostaglandins are messenger lipids that are C20-fatty-acid derivatives containing a cyclopentane ring and oxygen-containing functional groups. They are involved in raising body temperature, inhibiting gastric juice secretion, increasing the secretion of a protective mucus layer in the stomach, relaxing and contracting smooth muscle, directing water and electrolyte balance, intensifying pain, and enhancing inflammation responses. Most anti-inflammatory drugs decrease prostaglandin synthesis by inhibiting the action of enzymes necessary for their synthesis. COX-2 inhibitors specifically target COX-2 without inhibiting COX-1, thus reducing inflammation while preserving protective prostaglandins for the stomach lining.

A fatty acid is a naturally occurring monocarboxylic acid that nearly always contains an even number of carbon atoms and has an unbranched carbon chain. A monounsaturated fatty acid is characterized by having one carbon-carbon double bond in its structure.

Deficiency in essential fatty acids can lead to skin irritation, increased risk of infections, dehydration, and liver abnormalities, which can be reversed by restoring these acids in the diet.

The nonpolar tail chains (hydrophobic) are insoluble in water but soluble in nonpolar substances, while the polar head group (hydrophilic) is soluble in water.

'Bad cholesterol' is associated with LDLs and increases blood cholesterol levels, while 'good cholesterol' is associated with HDLs and helps reduce blood cholesterol levels.

The major mineralocorticoid hormone is aldosterone. Androgens promote the development of male secondary sex characteristics and muscle growth.

Thromboxanes are messenger lipids that promote the formation of blood clots and are produced by blood platelets, promoting platelet aggregation.

A polyunsaturated fatty acid is a fatty acid with a carbon chain in which two or more carbon-carbon double bonds are present. An omega-3 fatty acid has its endmost double bond three carbon atoms away from its methyl end, while an omega-6 fatty acid has its endmost double bond six carbon atoms away from its methyl end.

The two essential fatty acids are linoleic acid (omega-6) and linolenic acid (omega-3), which are necessary for various bodily functions.

Phosphatidylcholines, also known as lecithins, are found prevalently in cell membranes and are good dietary sources from egg yolks and soybeans.

Eicosanoids mediate inflammatory response, production of pain and fever, regulation of blood pressure, induction of blood clotting, control of reproductive functions, and regulation of the sleep/wake cycle. They are derived from oxygenated C20 fatty acids, primarily arachidonic acid.

The two methods are based on the biochemical function of a lipid and whether a lipid can be broken down into smaller units through basic hydrolysis (saponification). Saponifiable lipids undergo hydrolysis in basic solution to form soaps, while nonsaponifiable lipids do not undergo hydrolysis and cannot be broken down into smaller units.

Triacylglycerols are lipids that function as energy-storage materials in the body, concentrated primarily in adipocytes found in adipose tissue.

A micelle is a spherical cluster of molecules where the polar portions are on the surface and the nonpolar portions are in the interior, formed by the cleansing action of soap.

The distinguishing features of steroids include the location of double bonds within the fused-ring system and the nature and location of substituents. The steroid nucleus is based on a fused-ring system with three 6-membered rings and one 5-membered ring.

Long-chain saturated fatty acids tend to be solids at room temperature due to their higher saturated fatty acid content, which allows for close packing.

Phospholipids are the most abundant type of membrane lipid and make up to 80% of the mass of a cell membrane, which confines the cell's contents.

Sphingophospholipids consist of one fatty acid, one phosphate group attached to sphingosine, and an alcohol attached to the phosphate group, featuring two ester linkages and one amide linkage.

A cell membrane separates a cell’s aqueous interior from the surrounding aqueous environment and controls the movement of substances into and out of the cell. The two general types of membrane proteins are integral membrane proteins, which penetrate the cell membrane, and peripheral membrane proteins, which are located on the membrane's surface.

The two major classes of steroid hormones are sex hormones and adrenocorticoid hormones. Estrogens are responsible for the development of female secondary sex characteristics and regulation of the menstrual cycle.

Emulsification lipids, such as bile acids, aid in fat digestion and absorption. Bile acids are cholesterol derivatives that act as lipid-emulsifying agents in the digestive tract.

Saturated fats are considered 'bad fat' as they can increase the risk of heart disease, while monounsaturated fats are seen as 'good fat' as they can decrease risks of heart disease and breast cancer.

The three amino alcohols are choline, ethanolamine, and serine.

Plasma lipoproteins have a spherical structure with a central core of lipid material surrounded by a shell of phospholipids, cholesterol, and proteins. Chylomicrons transport dietary triacylglycerols from the intestine to the liver and adipose tissue.

Nonsaponifiable lipids are lipids that do not undergo hydrolysis in basic solution and cannot be broken into smaller parts.

Messenger lipids act as signaling molecules, including steroid hormones and eicosanoids, which mediate various physiological effects.

Omega-3 fatty acids, found in fish, are linked to lower heart disease incidence, while omega-6 fatty acids, found in plant oils, are more prevalent in the U.S. diet and can have different health effects.

A phospholipid contains one or more fatty acids, a phosphate group, a platform molecule (like glycerol or sphingosine), and an alcohol attached to the phosphate group.

Cholesterol is a C27 steroid molecule with a specific arrangement including an alcohol functional group at carbon 3, methyl group attachments at carbons 10 and 13, and a carbon-carbon double bond between carbons 5 and 6. Cholesterol is found in cell membranes, nerve tissue, brain tissue, and virtually all bodily fluids.

Short-chain fatty acids have slight solubility in water due to the polarity of the carboxyl group present. Water solubility for fatty acids is directly related to carbon chain length; solubility decreases as carbon chain length increases.

Fats contain triacylglycerols with mostly saturated fatty acids, allowing close packing and resulting in higher melting points, while oils contain more mono- and polyunsaturated fatty acids, which cause bends in the chains and lead to lower melting points.

Triacylglycerols serve as storage molecules for metabolic fuel, while glycerophospholipids function as components of cell membranes and are not stored.

HDL collects excess cholesterol from body tissues and transports it back to the liver for degradation to bile acids.

The common characteristic is solubility; all lipids are insoluble in water but soluble in nonpolar organic solvents.

A high dietary intake of triacylglycerols (fats and oils) is generally associated with higher rates of heart disease and certain cancers.

A glycerophospholipid contains two fatty acids, a phosphate group esterified to a glycerol molecule, and an alcohol esterified to the phosphate group.

Cholesterol serves as a component of cell membranes and a precursor for other steroid-based lipids. An imbalance can lead to increased blood cholesterol levels, contributing to atherosclerosis.

Biological waxes are monoesters of a long-chain fatty acid and a long-chain alcohol, generally saturated, containing from 14 to 36 carbon atoms in fatty acids, and 16 to 30 carbon atoms in alcohols. They protect hair and skin, keep skin pliable and lubricated, impart water repellency to animal fur, aid aquatic birds in keeping feathers water-repellent, minimize body heat loss in cold water, prevent excessive water evaporation in arid region plants, protect against parasite attacks in plants, and coat insects for protection. The general structural formula for a biological wax is similar to that for a simple ester, but both R and R' must be long carbon chains, usually containing 20 to 30 carbon atoms.

Saturated fatty acids (SFAs) have no carbon-carbon double bonds, while unsaturated fatty acids include monounsaturated (MUFAs) and polyunsaturated fatty acids (PUFAs) which contain one or more double bonds, respectively. Fatty acids are classified as long-chain (C12 to C26), medium-chain (C8 and C10), or short-chain (C4 and C6) fatty acids.

The melting points decrease with increasing degree of unsaturation. Unsaturated fatty acids have fewer intermolecular attractions due to their 'bends' from double bonds, preventing tight packing.

Linoleic acid is used to produce arachidonic acid (20:4), a key precursor for eicosanoids, which help regulate blood pressure, clotting, and other functions.

Cerebrosides are the simplest sphingoglycolipids containing a single monosaccharide unit, primarily found in the brain and in the myelin sheath of nerves. Gangliosides are more complex sphingoglycolipids containing a branched chain of up to seven monosaccharide residues, found in the gray matter of the brain and in the myelin sheath.

A triacylglycerol is formed by the esterification of glycerol with three fatty acids. A simple triacylglycerol is formed from three identical fatty acids, while a mixed triacylglycerol is formed from more than one kind of fatty acid.

Hydrogenation is the addition of hydrogen to double bonds, which increases saturation and the melting point of triacylglycerols.

Sphingomyelin is a specific type of sphingophospholipid where the alcohol esterified to the phosphate group is choline, found in all cell membranes and important for the myelin sheath.

The major function of lipoproteins is to help suspend lipids and transport them through the bloodstream. The four major classes of plasma lipoproteins are Chylomicrons, Very-low-density lipoproteins (VLDL), Low-density lipoproteins (LDL), and High-density lipoproteins (HDL).

Saponifiable lipids are lipids that undergo hydrolysis in basic solution, yielding two or more smaller product molecules. Ester linkages, amide linkages, and glycosidic linkages can be hydrolyzed in saponifiable lipids. The types of linkages (bonds) that hold the component parts together determine whether a lipid is saponifiable. A saponification reaction is a hydrolysis reaction carried out in basic solution.

An imbalance can lead to the precipitation of crystallized cholesterol and the formation of gallstones in the gallbladder. Cholesterol molecules regulate membrane rigidity and fit between the fatty acid chains of the lipid bilayer, restricting their movement.

Eicosanoids act locally in the tissues where they are synthesized and have profound physiological effects at extremely low concentrations.