Lecture 24: Lipids + Fatty Acids

Biological Roles of Lipids and Fatty Acids

• Energy Stores

• Structural Supports

• Signalling Molecules (Hormones, Cofactors, Binding Sites)

• Light Absorbing Pigments

• Electron Carriers

Unsaturated

possessing at least one carbon to carbon double bond

Fatty Acids

Carboxylic acids with a 4-36 unbranched carbon chain

Fatty acid Nomenclature

1. Determine the Root (the number of carbons
   →1 = mono, 2 = di, …, 16 = hexadecane

2. Convert Alkane to fatty acid
   → replace -e with -oic acid
   → or if there is a double bond: replace -e with [# of double bonds]enoic acid

3. Place ratio of carbons to double bonds in front of name
   → [total carbons]:[double bonds] eg: 18:1

4. State where double bonds are
   →use Δ^ + position(s), counted from the carboxyl end
   eg: Δ^(9,13)

Unsaturated Fatty Acid Nomenclature

Based on the number of double bonds:

• 1 = ___enoic acid

• 2= ___dienoic acid

• 3 = ___trienoic acid

And indicate the position of the double bond with: [total carbons] : [# of double bonds] (∆^[carbon number with double bond],…)

→ex: 20:5(∆^5,8,11,14,17) Eicosapentaenoic Acid

Palmitic Acid - Carbon skeleton, structure, systemic name

• Carbon skeleton: 16:0

• Structure: CH3(CH2)14COOH

• Systemic Name: n-Hexadecanoic acid

Stearic Acid

Carbon skeleton: 18:0

Structure: CH3(CH2)16COOH

Systemic Name: n-Octadecanoic acid

Oleic Acid

• Carbon skeleton: 18:1(∆⁹)

• Structure: CH 3−(CH 2) 7−CH=CH−(CH 2) 7−COOH

• Systemic Name: cis-9-Octadecenoic acid

Linoleic Acid

• Carbon skeleton: 18:2(Δ^9,12)

• Structure: CH₃(CH₂)₄CH=CHCH₂CH=CH(CH₂)₇COOH

• Systemic Name: cis-,cis-9,12-Octadecadienoic aicd

α-Linolenic acid

• Carbon skeleton: 18:3(Δ^9,12,15)

• Structure: CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH=CH=CH(CH2)COOH

• Systemic Name: cis-,cis-,cis-9,12,15-Octadecatrienoic acid

Arachidonic acid

• Carbon skeleton: 20:4(Δ^5,8,11,14)

• Structure: there's no way I gotta now this

• Systemic Name: cis-,cis-,cis-,cis-5,8,11,14-Icosatetraenoic acid

Naming ω-fatty acid (omega)

When naming you count from ω-C

ω-3 fatty acid

Derrived from alpha-linolenate and is an essential fatty acid

ω-6 fatty acid

Derrived from linoleate and is an essential fatty acid

ω-9 fatty acid

derived from oleate, is not essential

Triacylglycerols

Used for fatty acid storage wherein Glycerol is esterified to 3 fatty acids

TAGs

more concentrated energy source than glycogen with more energy released on oxidation. Can store months of stores

Glycogen

• is highly hydrated energy storage

• more rapidly accessable than TAG

• contains less than a day of stores

Classes of Membrane Lipid

• Phospholipids

• Glycolipids

• Cholesterol

Amphipathic

one end of a membrane is hydrophobic while the other is hydrophilic

Phospholipids are composed of

• Fatty acids →hydrophobic

• A Glycerol and Sphingosine backbone

• A Polar head group composed of Phospate and Alcohol, that faces the opposite direction than the fatty acids

Serine

Ethanolamine

Choline

Glycerol

Inositol

Glycolipids

Composed of:

• Sugar head group

• Sphingosine backbone

• Cerebroside (Glucose or Galactose)

• Globoside (sugars)

• Ganglioside→ more branched oligosaccharide that is negatively charged

Cholesterol (sterols)

Sphingosine

How to determine type of omega fatty acid (ω-X, how to find X)

Total amount of carbons - # carbon of last double bond

→EX: 22:6 ∆^{4,7,10,13,16,19} →22-19 = 3 → omega-3 fatty acid