LIPIDS AND FATTY ACIDS

Lipids

• are heterogeneous class of naturally occurring organic compounds classified together on the basis of common solubility properties

• insoluble in water, but soluble in aprotic organic solvents including diethyl ether, chloroform, methylene chloride, and acetone

• Amphipathic in nature

Open Chain forms

fatty acids, triacylglycerols, sphingolipids, phosphoacyl glycerols, glycolipids, lipid-soluble vitamins prostaglandins, leukotrienes, and thromboxanes

Cyclic forms

cholesterol, steroid hormones, and bile acids

• Fuel molecules

• Highly concentrated energy stores

• Signal molecules

• Components of membranes

Four primary functions of lipids

• Fatty acids

• Glycerol

• Sphingosine-derived lipids

• Steroids

• Terpenes

• Aromatic compounds

• alcohols

• waxes

Major classes of lipids

Sphingosine-derived lipids

(including the ceramides, cerebrosides, gangliosides, and sphingomyelins)

• Functionally analagous to glycerolipids

Steroids

– e.g., cholesterol

– basic skeleton consisting of four interconnected carbon rings; different structure than long chain FAs

– These molecules bind to specific protein receptors, precipitating a signal transduction chain

Terpenes

– Built from same 5-carbon precursor as cholesterol (isopentenyl pyrophosphate)

– Compounds also called isoprenoids

Fatty acid

is an unbranched-chain carboxylic acid derived from hydrolysis of animal fats, vegetable oils, or phosphodiacylglycerols of biological membranes

Myristic acid

often found attached to the N-term of plasma membrane- associated cytoplasmic proteins

Numerical symbol 14:0

Palmitic acid

end product of mammalian fatty acid synthesis

Numerical symbol 16:0

Palmitoleic acid

major monounsaturated fatty acid (MUFA) in humans:omega 7 FA

Numerical symbol 16:1

Oleic acid

major monounsaturated fatty acid (MUFA) in humans, omega-9 fatty acid

Numerical symbol 18:0

Linoleic acid

essential fatty acid omega-6 polyunsaturated fatty acid (PUFA)

a-Linolenic acid (ALA)

essential fatty acid omega-3 polyunsaturated fatty acid (PUFA)

Arachidonic acid

omega-6 polyunsaturated fatty acid (PUFA) precursor for eicosanoid synthesis

Eicosapentaenoic acid (EPA)

omega-3 polyunsaturated. fatty acid (PUFA) enriched in fish oils, Krill oil, and cyanobacteria

Docosahexaenoic acid (DHA)

omega-3 polyunsaturated fatty acid (PUFA) enriched in fish oils, Krill oil, and cyanobacteria

Saturated fatty acids

Fatty acids that have the maximum number of hydrogen atoms possiboe and no double bonds

Unsaturated fatty acids

Fatty acids that have one or more double bonds

Hydrogenation

is the process of converting unsaturated fats to saturated fats by adding hydrogen

trans fat

may contribute more than saturated fats to cardiovascular disease

adipose cells

Humans and other mammals store their fat in

addipose tissue

cushions vital organs and insulates the body

Triacylglycerols

an ester of glycerol with three fatty acids

saponification

natural soaps are prepared by boiling triglycerides (animal fats or vegetable oils) with NaOH, in a reaction called

Ca(II), Mg(II), and Fe(III) ions (hard water)

Soaps form water-insoluble salts when used in water containing -

phosphatidic acid

When one alcohol group of glycerol is esterified by a phosphoric acid rather than by a carboxylic acid, - is produced

Phosphoacylglycerols (phosphoglycerides)

are the second most abundant group of naturally occurring lipids. They are found in plant and animal membranes

Waxes

• A complex mixture of esters of long-chain carboxylic acids and alcohols

• Found as protective coatings for plants and animals

• Paraffin chains on either side of ester

Sphingolipids

• do not contain glycerol, but they do contain the long-chain amino alcohol sphingosine

• found in both plants and animals; they are particularly abundant in the nervous system.

Sphingomyelins

are amphipathic; they occur in cell membranes in the nervous system.

Glycolipids

• a carbohydrate bound to an alcohol group of a lipid by a glycosidic linkage

Steroids

• a group of lipids that have fused- ring structure of 3 six-membered rings, and 1 fivemembered ring.

Cholesterol

• precursor of other steroids and of vitamin D3.

• best known for its harmful effects on health when it is present in excess in the blood.

atherosclerosis

a condition in which lipid deposits block the blood vessels and lead to heart disease

hydrophobic interaction

the major force driving the formation of lipid bilayers

prokaryotes

The membranes of —, which contain no appreciable amounts of steroids, are the most fluid

cholesterol

The presence of — reduces fluidity by stabilizing extended chain conformations of hydrocarbon tails of FA due to hydrophobic interactions

• N-myristoyl- and S-palmitoyl anchoring motifs

• Anchors can be:N-terminal GlyThioester linkage with Cys

Proteins Can be Anchored to Membranes through

Mosaic

components in the membrane exist side-by-side as separate entities.

simple diffusion

a molecule or ion moves through an opening

facilitated diffusion

a molecule or ion is carried across a membrane by a carrier/channel protein

Active transport

a substance is moved AGAINST a concentration gradient

primary active transport

transport is linked to the hydrolysis of ATP or other high-energy molecule; for example, the Na+/K+ ion pump

secondary active transport

Transport driven by H+ gradient

Passive Transport

• Passive diffusion of an uncharged species across a membrane depends only on the concentrations (C1 and C2) on the two sides of the membrane.

• A substance moves from a region of higher concentration to one of lower concentration

Active Transport

• Requires moving substances against a concentration gradient.

• It is identifi ed by the presence of a carrier protein and the need for an energy source to move solutes against a gradient.

• Directly linked to the hydrolysis of a high-energy molecule, such as ATP

Trans Fat

produced industrially by the partial hydrogenation of any liquid oils, in most cases vegetable oils, but also occurs naturally in meat and dairy products from ruminant animals.

oxidative stability

The better an oil can resist oxidation the better it is for cooking. This quality is measured as -