LipidsB.4

3 Main Types of Lipids (B.4.1…)

• ‘lipid’ comes from lipos, the Greek word for fat

• all are hydrophobic (water-fearing/insoluble in water)

• greasy, oily

1. Triglycerides (fats and oils)• found in adipocyte cells that are in fatty tissue• condensation reactions cause 3 fatty acids chains

(16-22 carbon atoms) to covalently bond to a molecule of glycerol (B.4.6)

– produces 3 molecules of water– this bond between a carboxyl group (on the fatty acid)

and an hydroxyl group (on the glycerol) is called an ester linkage

http://www.google.com/url?sa=i&rct=j&q=triglycerides&source=images&cd=&cad=rja&docid=R5qMxf5A5TnRJM&tbnid=jvfqAjnf4yu_AM:&ved=0CAUQjRw&url=http://www.articlesbeach.com/disease-illness/triglycerides-symptoms-causes-remedies/&ei=_XSdUdPXBserjALeyYCgDg&bvm=bv.46865395,d.cGE&psig=AFQjCNEfiLYqMhnGf-QRZrkG-i8FyivwSA&ust=1369359970909688

• the fatty acids found in triglycerides (and other lipids) are either: (B.4.3)

- saturated fat- do NOT contain C=C bonds

- therefore straight chained and have high melting points

- lard and butter - unsaturated fat

- have double bonds between one (monounsaturated fats) or more (polyunsaturated fats) of the carbons in the chain

- causes a kink in the carbon chain which prevents them from packing close together and therefore have low melting points (Van der Wall’s forces are weaker)

- vegetable oils

Saturated vs. Unsaturated fatty acids (2:51)

Common Fatty AcidsName Formula # of C # of C=C

bondsMelting

pt (Co)

Source

Saturated Fatty AcidsLauric

Acid CH3-(CH2)10-COOH 12 0 44.2 Coconut Oil

Myristic Acid CH3-(CH2)18-COOH 14 0 54.1 Nutmeg, Palm Oil, Butter

Palmitic Acid CH3-(CH2)14-COOH 16 0 62.7 Palm Oil

Stearic Acid CH3-(CH2)16-COOH 18 0 69.6 Animal and vegetable fats

Unsaturated Fatty Acids

Oleic Acid

CH3-(CH2)7CH=CH-(CH2)7COOH 18 1 10.5 Corn Oil

Linoleic Acid

CH3-(CH2)4 CH=CH-CH2-CH=CH –

(CH2)7COOH

18 2 -5.0 Linseed Oil

10

Iodine number and C=C bonds (B.4.5)

• the addition of iodine is used to determine the # of C=C bonds– iodine causes the double bonds to break and form single

bonds

– one mole of C=C requires one mole of I2 to react

• iodine is purple– as iodine is added to unsat fat, the purple color disappears

as the addition reaction takes place• iodine index is the # of grams of iodine that reacts

with 100 g of unsat fat

1 1

Iodine Index of Common Fats/ Oils

Oil or fat Percentsaturated

fats

Percent of monounsaturated fats

Percent of polyunsaturated fats

Iodine Index

Butter fat 67% 29% 4% 34BeefTallow

52% 44% 4% 50

Olive Oil 15% 75% 10% 81

Peanut Oil 18% 49% 33% 93

Canola Oil 7% 62% 31% 130Sunflower

oil10% 13% 77% 125

Example problem

• 0.010 mol of linoleic acid (C18H32O2) reacts with 5.1 g of iodine. Determine the number of double bonds present in linoleic acid.

5.1 g I2 1 mol I2

254 g I2

• therefore, 0.010 mol of linoleic acid reacts with 0.020 mol of I2

– 1:2 ratio– linoleic acid must have two double bonds

X = 0.020 mol I2

Compare essential fatty acids and state their importance (B.4.4)

• primary structural components of cell membranes

• essential fatty acids are those that the body cannot synthesize on its own– must be acquired from the foods we eat– these are linoleic (omega-6 fatty acid) and linolenic (omega-

3-fatty acid)

• important…– precursors for larger fatty acids– promote healthy immune system– maintain healthy cholesterol levels

15

Compare omega-3 and omega-6 fatty acids

omega-6 linoleic acid

• obtained from seeds and vegetables• the omega-6 indicates that there is a C=C on the 6th

carbon from the end of the carbon chain

17

omega-3 linolenic acid

• obtained from green leaves• the omega-3 indicates that there is a C=C on

the 3rd carbon from the end of the carbon chain

Hydrolysis of triglycerides (B.4.7)

• the splitting of covalent bonds using water• the reverse of making triglycerides• digestion splits fat into carboxylic acids and

glycerol– the enzyme lipase is necessary

http://www.google.com/url?sa=i&rct=j&q=Hydrolysis+of+triglycerides&source=images&cd=&cad=rja&docid=EhK5w3YmHBfA4M&tbnid=uMALVgRUtmAAoM:&ved=0CAUQjRw&url=http://catalog.flatworldknowledge.com/bookhub/reader/2547?e=gob-ch20_s02&ei=F1-YUZGHH-POiwK5jYDIDA&bvm=bv.46751780,d.cGE&psig=AFQjCNFmTUNYfGHkXRDUORlfihZ2lTeF9w&ust=1369026650210882

2. Phospholipids• major structural components of cell membranes• like triglycerides, but one of the fatty acids is

replaced by a phosphate group that is negative and a nitrogen group that is postive– this caused the “heads” to love water (hydrophilic)

• the uncharged “tails” avoid water (hydrophobic)

+ _

+_

+ _

+_

3. Steroids• cholesterol is the most abundant and important steroid

– maintains fluidity in cell membranes– the precursor of other important steroids – can contribute to heart disease

• structurally diff. from other lipids– contain four interlocking rings of carbon and

hydrogen

• lipoproteins – molecules made of proteins and fat– transport cholesterol around the body (B.4.2)– low density lipoproteins (LDL) “bad cholesterol”

• transport cholesterol to cells to be used• however, can build up and cause cardiovascular disease

– high density lipoproteins (HDL) “good cholesterol”• doesn’t have much cholesterol, therefore, can abosrb

more cholesterol from the arteries and transports it back to the liver

Lipids important roles and negative effects on health (B.4.9)

• important roles:– energy storage- fat in humans– fats provide our most concentrated form of energy

with 37 kJ/gram vs. carbohydrates with 16 kJ/gram• have less oxygen than carbs

– therefore, more oxidation can take place which releases more energy

– insulation and protection– structural component of cell membranes

• negative effects– increased risk of heart disease from elevated LDL’s– obesity