Lipids: What do you need to know? o Classification of major lipid groups o Structure of fatty acids o Physical properties of fatty acids o Structure &

Lipids: What do you need to know?

o Classification of major lipid groupso Structure of fatty acidso Physical properties of fatty acidso Structure & function of triacylglycerolso Chemical reactions of triacylglycerolso Compare phospholipids & glycolipidso Composition & properties of membrane lipidso Structure & function of cholesterolo Compare & contrast 3 types of cellular membrane transporto Compare & contrast some steroid hormoneso Structure & function of bile acidso Compare & contrast 3 types of eicosanoidso Structure & function of biological waxes

Fats and oils are the most widely occurring types of lipids. Thick layers of fat help insulate polar bears against the effects of low temperatures.

A lot of structural variety is represented by lipids.

They are typically:

- insoluble in H2O

- soluble in NP

solvents

Lipid Categories (based on function)

• Energy Storage– Triacylglycerols (fats)

• Membrane structure– Phospholipids, Sphingoglycolipids, cholesterol

• Emulsification– Bile acids

• Messenger molecules– Steroid hormones; eicosanoids

• Protective coating– Biological waxes

Lipid Building Blocks - Fatty Acids (F.A.)

• Fatty Acids = monocarboxylic acids– Straight chains

• Long: C12-C26

• Medium: C8 & C10

• Short: C4 & C6

– Saturated (SFA)– Monounsaturated (MUFA)– Polyunsaturated (PUFA)

• Usually </= 6 double bonds

– Almost always known by common names

All of these are 18 carbon chains

Various formulas can be used to draw the long chains:

e.g. 14 carbons long

Structural Notation for F.A.

• F.A. With 18 C atoms and 1 double bond (MUFA).

F.A. -COOH end Methyl end

SFA no ∆ notation no notation

MUFA usually ∆9 -3 or-9

PUFA generally ∆9,12,

(15)

-3 or-6

Physical Properties

• Water solubility decreases with increasing # C atoms

• MP increases with increasing # C atoms

• MP decreases with increasing unsaturation– Straight chains pack well– Bent chains don’t pack well

Four 18-carbon fatty acids, which differ in the number of double bonds present.

Compounds with

double bonds, or rings:

Observe attached groups

lying above or below

plane of double bond or ring.

"cis" groups on same side.

"trans" groups are across.

Different isomers have

different physical and

sometimes different

chemical properties.

Quick review of cis/trans isomerism:

Cis pattern creates bent molecules.This affects the intermolecular bonding

If there is more than one double bond, they occur at three-carbon intervals.

-C=C-C-C=C-This is called the divinylmethane pattern.

Space-filling models of four 18-carbon fatty acids, which differ in the number of double bonds present.

Note how the presence of double bonds changes the shape of the molecule.

Common names derive from a common source of

the compound or the source from which it was first

isolated.

e.g. Palmitic acid is found in palm oil

Oleic acid - a major part of olive oil (oleum)

Stearic (from Greek word for “solid”) acid

is solid at room temperature.

Spiders (Arachnids) contain arachidonic acid.

In IUPAC system, carboxyl carbon is number one. All bonds reference the carboxyl carbon.

e.g. a double bond between 9th and 10th C is at the 9-carbon + a Greek name

cis-9- hexadecanoic acid (16 carbons)

These names are awkwardly long so aren’t used as commonly as some of the other systems

Essential fatty acids:alpha-linolenic acid (ALA, an omega-3) and linoleic acid (an omega-6)Human body needs, but cannot manufacture, them. When sufficient quantities are supplied in the diet, the body can make enough Docosahexaenoic acid (DHA)and eicosapentaenoic acid (EPA) to createthe eicosanoids that form our metabolic "thermostat" system

Also affect brain development and function.Lack of these can cause:

Depression, ADHD, Alzheimers, & Inflammation

Triacylglycerols = Triglycerides = Triesters

Adipoctyes are the body’s triacylglycerol-storing cells.

Simple

mixed

Triple esterification reaction between glycerol and 3 molecules of stearic acid (18:0 fatty acid).

Three molecules of water are a by-product of this reaction.

Dehydration synthesis (condensation rxn) of a simple Triacylglycerol (triglyceride)

Fats vs. Oils• Fats: typically are solids at room temp.

– Mostly SFAs– Generally from animals

Warm-blooded organismsFluid at warmer temperatures

• Oils: typically are liquids at room temp.– Lots of MUFAs and PUFAs

– Generally from plantsMore kinks in the chain, the more fluid the oil.Makes cell membranes flexible and permeable, allowing nutrients in & waste products out.

Lipids & your Diet

• General population correlation– High triglyceride intake = increased risk of heart disease & certain cancers

• But... Inuit...,etc.

• “Good” vs. “Bad” fats– SFA = “Bad”– MUFA = “Good” cold water fish (-3 FA)

– PUFA -3 = “Good” -6 = “Bad”