biochem study guide exam 2 fatty acids

What is a fatty acid? Describe its basic chemical structure and explain the meaning of the carboxyl end and methyl end.

Hydrocarbon chain with a carboxylic acid

functional group at carbon 1

• In foods and in blood, about 95-99% are

esterified (i.e., bonded to an alcohol

compound: glycerol, cholesterol, fat soluble

vitamins, sphingosine)

• In blood, 1-5% found also as free fatty acids

bonded to albumin (non- or un-esterified

fatty acids), higher concentrations during

fasting and physical activity

14. How are fatty acids classified according to chain length and degree of saturation?

Straight hydrocarbon chain

• Contain an even number of carbon atoms (2-

30) (short, medium, long, and very long chain)

– Odd numbered formed by bacteria and processing

• Hydrocarbon chain can be

– Saturated (contain no double bonds)

– Unsaturated (contain one or more double bonds)

• Contain one (monounsaturated) or more

(polyunsaturated) cis-double bonds

• Trans-unsaturated formed by bacteria, during food

processing, or cooking from cis-unsaturated

(isomerization)

Naming FA (IUPAC)

Saturated FA (alkanes) = suffix anoic acid;

octanoic acid (octa = 8 carbon saturated fatty

acid)

• Unsaturated FA (alkenes) = suffix enoic acid;

octadecenoic acid (octa = 8 and deca = 10,

thus 18 carbon unsaturated fatty acid)

Carbon atoms are numbered starting from

carboxylic acid carbon (#1)

For unsaturated FA: where (#) and type (cis vs

trans) of double bond(s) is important

• Two major ways: delta (triangle) or omega (square)

naming system

15. Compare saturated, monounsaturated, and polyunsaturated fatty acids in terms of their carbon–carbon bonds.

monounsaturated: one double bond

polyunsaturated: two or more double bonds

saturated: no double bonds

how do cis and trans double-bond configurations differ, and how can these configurations affect fatty-acid shape and physical properties?

hydrogen arrangement: in cis config the hydrogen atoms adjacent to carbon double bonds are positioned on same side of the chain

in trans, h atoms are positioned on opposite sides

differ in packing and melting points

Explain how chain length and degree of saturation influence fatty-acid melting point. Include the role of packing between hydrocarbon chains.

The melting point of a fatty acid is directly determined by how closely its hydrocarbon tails can pack together and the strength of the intermolecular London dispersion forces (Van der Waals forces) between them

longer chain length = higher melting point

what does fatty-acid notation such as 18:1 or 20:5 communicate? Explain how to interpret the number of carbons and the number of double bonds.

18 carbons 1 cis double bond

how is omega nomenclature assigned? Explain how the omega end is identified and how an omega-3 fatty acid differs from an omega-6 fatty acid.

based on the position of their first carbon–carbon double bond relative to the methyl (tail) end of the molecule

count carbons from the methyl end to double bond, omega-3 fatty acid’s double bond is 3 carbons away from methyl end

Given a fatty-acid structure, describe a systematic approach for determining its carbon count, number of double bonds, and omega family.

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be able to connect common fatty acids discussed in class—such as palmitic acid, linoleic acid, EPA, and elaidic acid—with their structural or numerical characteristics. How would you distinguish them?

FAs

lauric acid: 12:0

myristic acid:14:0

palmitic acid:16:0

stearic acid18:0

PUFAs: 2 or more double bonds

linoleic: 18:2 cis 9,12

alpha linolenic: 18:3 cis 9,12,15

arachidonic:20:4 cis 5,8,11,14

EPA:20:5 cis5,8,11,14,17

What is hydrogenation, and how does it change an unsaturated fatty acid? How does this process differ from hydrolysis and oxidation?

Hydrogenation is a chemical process that adds molecular hydrogen H2 across the carbon-carbon double bonds of unsaturated fatty acids

• breaks carbon double bonds, increases saturation