[4] LIPIDS

LIPIDS

• A family of structurally diverse (do not have a universal component) compounds whose similarity is only their nonpolarity = water-insolubility/ immiscibility 

• Lipophilic = Hydrophobic

Uses of Lipids

• cell membranses

• storage of energy in bulk

• vitamins

• hormones

• emulsification

• protective coating

Uses of Lipids: cell membranes

• phospholipids

• sphingolipids

• cholesterol

Uses of Lipids: Storage of energy in bulk

• triacylglycerides

Uses of Lipids: vitamins

A, D, E, K

Uses of Lipids: hormones/ messenger

• steroidal hormones

• eicosanoids

Uses of Lipids: emulsification

bile acids

Uses of Lipids: protective coating

biological waxes

FATTY ACIDS

• Long-chain carboxylic acids; building blocks of lipids 

• Content of most important physiologic lipids

Physical Properties of Fatty acids: polarity/ solubility

Increased number of carbons increases lipophilicity

Physical Properties of Fatty acids: melting point

Reduced compactness due to cis double bonds reduces IMF and thus lowers melting point

Saturated fatty acids

• Contain only C-C single bonds 

• Compact molecules 

• Have relatively high melting points

solids

Long-chain saturated fatty acids tend to be __ at room temperature. 

6C saturated fatty acid

Caproic acid

8C saturated fatty acid

caprylic acid

10C saturated fatty acid

capric acid

12C saturated fatty acid

lauric acid

14C saturated fatty acid

myristic acid

16C saturated fatty acid

palmitic acid

18C saturated fatty acid

stearic acid

20C saturated fatty acid

arachidic acid

Unsaturated fatty acid

• Contain at least one C-C double bond 

• Not as compact as saturated fatty acids 

• Have relatively low melting points

liquids

Long-chain unsaturated fatty acids tend to be __ at room temperature. 

Nomenclature/ Notations of unsaturated fatty acids

• delta notation

• omega notation

Simplified (delta) nomenclature

start counting from the carboxyl end 

• 22:6 △5,8,11,14,17,20

Omega (ω) nomenclature

• position of double bonds relative to the last carbon

• start counting from the alkyl end

16:1 △6

palmitoleic acid (delta nomenclature)

omega-7

palmitoleic acid (omega nomenclature)

18:1 △9

oleic acid (delta nomenclature)

11:1 △10

undecyclenic acid (delta nomenclature)

18:2 △9,12

linoleic acid (delta nomenclature)

18:3 △9,12,15

linolenic acid (delta nomenclature)

20:4 △5,8,11,14

arachidonic acid (delta nomenclature)

20:5 △5,8,11,14,17

eicosapentanoic acid / EPA (delta nomenclature)

22:6 △4,7,10,13,16,19

docosahexanoic acid /DHA (delta nomenclature)

omega-3

linoleic acid & arachidonic acid (omega nomenclature)

omega-6

linolenic acid, EPA, DHA (omega nomenclature)

Linoleic & Linolenic acid

which are essential fatty acids?

increased heart disease risk

dietary effect of saturated fatty acids

decrease in heart disease risk

dietary effect of monounsaturated fatty acids

mixed; have several conflicting studies relative to heart disease risk

dietary effect of polyunsaturated fatty acids

reactions of fatty acids

• saponification

• rancidification

• hydrogenation

SAPONIFIABLE LIPIDS

Converted into two or more smaller molecules when hydrolysis occurs.

SAPONIFIABLE LIPIDS (examples)

• triacylglycerols

• phospholipids

• sphingolipids

• waxes

Triacylglycerols / Triglycerides

• Triester of glycerol (a trihydric alcohol) with three fatty acids 

• Neutral lipids

• May be simple (all 3 acyls the same) or mixed 

• Storage lipid (in adipose)

Phospholipids

• Similar structure to triglycerides 

• Acidic lipids 

• Structural lipids (found primarily in cell membrane)

Phosphatidic acid

none

Phosphatidylcholine (PC)

choline

Phosphatidylserine (PS)

serine

Phosphatidylethanolamine (PE)

ethanol-amine

Phosphatidylinositol (PI)

Sphingolipids

• Use a sphingosine backbone 

• Structural lipids (found primarily in nerve tissue)

Ceramide

none

Cerebroside

Glu/Gal

Globoside

oligosaccharide

Ganglioside

polysaccharide (with sialic & neuraminic acid)

Sphingomyelin

Phosphate & choline

Waxes

• Esters of fatty acid with a long chain, monohydric alcohol 

• Have higher melting points and are rigid compared to other lipids

Glycerolipids include

• triacylglycerol

• glycerophospholipid

Phospholipids include

• glycerophospholipid

• sphingophospholipid

Sphingolipids include

• sphingophospholipid

• sphingoglycolipid

NON-SAPONIFIABLE LIPIDS

• Cannot be broken up into smaller units since they do not react with water. 

NON-SAPONIFIABLE LIPIDS (examples)

• fat-soluble vitamins

• sterols

Fat-soluble Vitamins: vitamin A

• retin

• eyesight

Fat-soluble Vitamins: vitamin D

• calciferol

• Bones (with the help of kidney hydroxylases)

Fat-soluble Vitamins: vitamin E

• tocopherol

• antioxidant

Fat-soluble Vitamins: vitamin K

• mena (menaquinone)

• coagulation

Sterols

Contain the cyclopentanoperhydrophenanthrene (CPPP) ring

Sterols (examples)

• Cholesterol

• ergosterol

• phytosterols

Importance of Cholesterol

• Regulates fluidity of cell membranes 

• Precursor of bile acids 

• Precursor of vitamin D 

• Precursor of steroid hormones

steroid hormones include

• Glucocorticoids (ex. cortisol) 

• Mineralocoticoids (ex. aldosterone) 

• Sex hormones (ex. testosterone, estradiol, progesterone)