Lipids B.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

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 Acids NameFormula # of C# of C=C bonds Melting pt (C o ) Source Saturated Fatty Acids Lauric Acid CH 3 -(CH 2 ) 10 -COOH Coconut Oil Myristic Acid CH 3 -(CH 2 ) 18 -COOH Nutmeg, Palm Oil, Butter Palmitic Acid CH 3 -(CH 2 ) 14 -COOH Palm Oil Stearic Acid CH 3 -(CH 2 ) 16 -COOH Animal and vegetable fats Unsaturated Fatty Acids Oleic Acid CH 3 -(CH 2 ) 7 CH=CH- (CH 2 ) 7 COOH Corn Oil Linoleic Acid CH 3 -(CH 2 ) 4 CH=CH-CH 2 - CH=CH – (CH 2 ) 7 COOH 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 I 2 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 fatPercent saturated fats Percent of monounsaturated fats Percent of polyunsaturated fats Iodine Index Butter fat 67%29% 4%34 Beef Tallow 52%44% 4%50 Olive Oil 15%75%10%81 Peanut Oil 18%49%33%93 Canola Oil 7%62%31%130 Sunflower oil 10%13%77%125

Example problem mol of linoleic acid (C 18 H 32 O 2 ) reacts with 5.1 g of iodine. Determine the number of double bonds present in linoleic acid. 5.1 g I 2 1 mol I g I 2 therefore, mol of linoleic acid reacts with mol of I 2 – 1:2 ratio – linoleic acid must have two double bonds X = mol I 2

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 6 th 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

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