CH 11: Lipids

Numbering from the omega end

(see picture in previous card)

Modified Fatty Acids

1) Cyclic 2) Branched

Triacylglycerols are formed when....

A glycerol is esterified with three fatty acids

Triacylglycerols (AKA Triglycerides)

A major energy source for many organisms: - Rich in highly reduced carbons (a gram of anhydrous fat stores more than six times the energy of a gram of hydrated glycogen.) - Aggregate into highly anhydrous forms - Not soluble in water, but soluble in benzene, chloroform, ether, and ethanol Can be hydrolyzed: - heating with acid or base (saponification) - treatment with lipases

Glycerophospholipids

Also known as phosphoglyceride or glycerol phosphatide Essential components of cell membranes Glycerophospholipids are phospholipids but not necessarily vice versa The nature of the FAs esterified to glycerol determines their physical and chemical properties

Ether Glycerophospholipids

An ether instead of an acyl group at C-1

Phospholipases

Breakdown of phospholipids Cleavage points in phosphatidylinositol 4,5-bisphosphate

Palmitate

CH₃(CH₂)₁₄COO⁻ 16:0 n-Hexadecanoatw

Stearate

CH₃(CH₂)₁₆COO⁻ 18:0 n-Octadecanoate

Linoleate

CH₃(CH₂)₄(CH=CHCH₂)₂(CH)₆COO⁻ 18:2n-6 (2 double bonds between C6 and C7, C9 and C10, count from distal end) cis,cis-∆⁹, ∆¹²-Octadecadienoate *essential fatty acid

Oleate

CH₃(CH₂)₇CH=CH(CH₂)₇COO⁻ 18:1n-9 (1 double bond between C9 and C10, count from distal end) cis-∆⁹-Octadecenoate *essential fatty acid

α-Linolenate

CH₃CH₂(CH=CHCH₂)₃(CH₂)₆COO⁻ 18:3n-3 (3 double bonds between C3 and C4, C6 and C7, C9 and C10, count from distal end) all,cis-∆⁹, ∆¹², ∆¹⁵-Octadecatrienoate *essential fatty acid

What is the most common sterol?

Cholesterol is the most common sterol and [recursor for all other steroids in animals

Cis polyunsaturated fatty acids are essential components of our diets because...?

Cis polyunsaturated fatty acids are essential components of our diets because humans cannot synthesize them. These fatty acids are precursors to a variety of hormones and appear to offer some protection from coronary heart disease. -Trans fats, or trans-fatty acids, are a form of unsaturated fat. -Natural, trans fats occur in the meat and dairy from ruminant animals, such as cattle, sheep, and goats, when bacteria in these animals' stomachs digest grass. -Industrial trans fats (partially hydrogenated fats) are formed when vegetable oils are chemically altered hydrogenated) to stay solid at room temperature, which gives them a much longer shelf life.

Composed of a long hydrocarbon chain (_____) and a terminal carboxyl group (______).

Composed of a long hydrocarbon chain (tail) and a terminal carboxyl group (head)

Arrange the following in order of increasing solubility in water. When acyl groups are present, assume they are equivalent. a. Glycerol b. 1,3-Diacylglycerol c. 2-Monoacylglycerol d. 1,2,3-Triacylglycerol

D, B, C, A

Classes of lipids and which to know for this class

For this class, know: 1) Fatty acids 2) Triacylglycerols 3) Glycerophospholipids 4) Sphingolipids 5) Steroids

Hormones derived from Cholesterol

Generally oxidized form of the steroid base that lack hydrophobic chain more soluble

Membrane lipids can include carbohydrates

Glycolipids are carbohydrate-containing lipids. The carbohydrate components of glycolipids are on the extracellular surface of the cell membrane, where they play a role in cell-cell interactions. Cerebrosides are the simplest glycolipids.

Ganglioside GM2

HO-³CH-CH=CH-(CH₂)₁₂-CH₃ | ²CH-HN- Fatty Acid | ¹CH₂-O- Complex oligosaccharide

Lactosylceramide

HO-³CH-CH=CH-(CH₂)₁₂-CH₃ | ²CH-HN- Fatty Acid | ¹CH₂-O- Di-, tri-, or tetrasaccharide

Glucosylcerebroside

HO-³CH-CH=CH-(CH₂)₁₂-CH₃ | ²CH-HN- Fatty Acid | ¹CH₂-O- Glucose

Ceramide

HO-³CH-CH=CH-(CH₂)₁₂-CH₃ | ²CH-HN- Fatty Acid | ¹CH₂-O- H

General structure of a sphingolipid

HO-³CH-CH=CH-(CH₂)₁₂-CH₃ | ²CH-HN- Fatty Acid | ¹CH₂-O- Head Group (X)

Sphingomyelin

Has an esterified phosphotidylcholine or phosphorylethanolamine in the 1-hydroxy group X group: Choline Fatty Acid: Palmitate HO-³CH-CH=CH-(CH₂)₁₂-CH₃ | ²CH-HN- Palmitate | ¹CH₂-O- Phosphocholine

Review: what is an ester?

In chemistry, an ester is a chemical compound derived from an acid (organic or inorganic) in which at least one -OH (hydroxyl) group is replaced by an -O-alkyl (alkoxy) group. Usually, esters are derived from a carboxylic acid and an alcohol.

Isoprenoids

Isoprenoids: -terpenoids or prenol lipids -Class of organic compounds composed of two or more units of hydrocarbons, with each unit consisting of five carbon atoms arranged in a specific (isoprene) pattern.

Cholesterol is essential for normal membrane functions because it: A) cannot be made by higher organisms, e.g. mammals. B) spans the thickness of the bilayer. C) keeps membranes fluid. D) plugs up the cardiac arteries of older men.

Keeps membranes fluid

Common membrane lipids

Membrane lipids (phospholipids, glycolipids, cholesterol) are amphipathic molecules. The fatty acid components (tail) provide the hydrophobic properties, while the alcohol and phosphate components, called the polar head group, provide the hydrophilic properties.

Lipids

Molecules that are not soluble in water, but are soluble in organic solvents Not polymers, but they forms specific aggregates (such as membranes) Chemically very diverse Involved in the formation of membranes, energy storage, signaling

Phosphatidic Acid

Name of glycerophospholipid: Phosphatidic Acid X is -H Net charge at pH 7 = -1

Phosphatidylcholine

Name of glycerophospholipid: Phosphatidylcholine Name of X: Choline ₊ Formula of X: -CH₂-CH₂-N(CH₃)₃ Net charge at pH 7 = -1

Phosphatidylethanolamine

Name of glycerophospholipid: Phosphatidylethanolamine Name of X: Ethanolamine ₊ Formula of X: -CH₂-CH₂-NH₃ Net charge at pH 7 = 0

Phosphatidylglycerol

Name of glycerophospholipid: Phosphatidylglyerol Name of X: Glycerol Formula of X: -CH₂-CH-CH₂-OH | OH Net charge at pH 7 = -1

Phosphatidylserine

Name of glycerophospholipid: Phosphatidylserine Name of X: Serine ₊ Formula of X: -CH₂-CH-NH₃ | COO- Net charge at pH 7 = -1

Fatty Acids to Know

Palmitic Acid Stearic Acid Oleic Acid Linoleic Acid alpha-Linoleic Acid

Platelet activating factor and Plasmalogens

Plasmalogens are ether glycerophospholipids with an unsaturated alkyl chain Platelet-activating Factor (PAF): R1=16:0 R2=CH3

Which one of the following is not one of the principle differences among fatty acids? a. Number of carbons b. The type of the functional head group c. Length of the chain d. Position of double bonds e. All are principle differences

Principle differences among fatty acids: a. number of carbons c. length of the chain d. position of double bonds Not a principle difference among fatty acids: b. The type of functional head group

Lipid attachment to proteins

Proteins are sometimes covalently bound to lipids to localize the protein to the cell membrane.

Saturated vs. unsaturated fatty acids

Saturated FAs: all single bonded C-atoms Unsaturated FAs: one or more double bonded C-atoms -monounsaturated -polyunsaturated

Soaps and Mammal Triacylglycerol Storage

Soaps are the sodium or potassium salts of fatty acids generated by treating triacylglycerols with a strong base. In mammals, the major site for triacylglycerol storage is adipose tissue. Each adipocyte (adipose cell or fat cell) contains a large lipid droplet in which the triacylglycerols are housed.

Fatty acid chains affects properties of food fats

Solid fats (butter, beef fat) have more saturated fatty acids Liquid fats (olive oil) have more unsaturated fatty acids

Steroids

Steroids: -Relatively rigid fused ring system and weakly polar groups -Have important consequences in membranes -Steroid hormones serve many functions in animals, including salt balance, metabolic function and sexual function

Fatty Acid Nomenclature (I)

Tail: long hydrocarbon chain Head: terminal carboxyl group Numbering starts with carboxylic acid or with Greek letters starting with 1st carbon AFTER carboxylic acid (last C is ω - omega)

The ____ linkages and branching structure of membrane ____ of extremophiles prevent _____ and ______ of membranes in harsh environments.

The ether linkages and branching structure of membrane lipids of extremophiles prevent hydrolysis and oxidation of membranes in harsh environments.

Fatty Acid Nomenclature (II)

The positions of double bonds are indicated with the symbol Δ, with the first atom of the double bond indicated by a superscript number. Δ⁹ indicates a double bond between carbon atoms 9 and 10. Because fatty acids are ionized at physiological pH, they are usually referred to as their carboxylate form rather than the unionized acid.

Some glycerophospholipid headgroups and which ones to know

To Know: 1) Phosphatidic Acid 2) Phosphatidylethanolamine 3) Phosphatidylcholine 4) Phosphatidylserine 5) Phosphatidylglycerol

Gangliosides

have 3 or more sugars, one of which is a sialic acid (have (-) charge at neutral pH)

Glycosphingolipids

have one (cerebroside) or more sugars in β-glycosidic linkage at the 1-hydroxyl group

Fatty acids structure and melting point

more double bonds: lower melting point This is the reason why animals in colder climates have evolved to have adipose tissue with more unsaturated fat. The double bonds help the fat to stay fluid at lower temperatures.

Sphingolipids

sphingosine backbone instead of glycerol

Sterols

subset of steroids with -OH in the C3 position Based on a core structure consisting of three 6- membered rings fused to one 5-membered ring

What is the major role of fat in our diets?

to provide energy to provide structural material to act as a precursor to signaling molecules

Fatty Acids- Physicochemical Characteristics

• Chains of hydrogen-bearing carbon atoms that have a carboxylic acid at one end and a methyl group at the other end. •The carboxyl group is normally ionized at physiological conditions •They are rarely free in nature, but rather esterified to glycerol or other backbones •Most have an even number of carbons (14-24)

Saturated Fatty Acids

•Flexible due to free rotation around C-C bonds •The fully extended conformation is the most stable due to steric constraints •Chains pack tightly against each other and form more rigid, organized aggregates (i.e., membranes)

Unsaturated Fatty Acids

•Unsaturated chains bend and pack in a less ordered way, with greater potential for motion •They contain typically 1-4 double bonds •The double bond is almost always in cis configuration, resulting in a "kinked" structure