Understanding Lipids: Structure, Classes, and Function

• Lipids are organic compounds relatively insoluble in water but soluble in organic solvents.

Fats vs Oils

• Fats are solid at room temperature whereas oils are liquid at room temperature.

Major Lipid Classes

• Fatty acids
• Triglycerides
• Phospholipids
• Sterols
• Fat-soluble vitamins

Classes of Lipids

• Fatty acids - long chain linear (unbranched) hydrocarbons with carboxylic acids
• Triglycerides - fatty acid esters of glycerol
• Phospholipids - lipids containing one or more phosphate groups
• Glycolipids - lipids containing a carbohydrate component
• Eicosanoids - derivatives of Arachidonic acid
• Steroids - possess a perhydrocyclo-pentanophenanthrene ring system
• Lipoproteins - complexes of lipids and proteins circulating in the blood

Fatty Acid Structure

• Consists of a chain of carbon atoms
• Has a carboxylic acid group at the alpha end (-COOH)
• Possesses a methyl group at the omega end

Number of Carbons

• Short-chain fatty acids: < 8 carbons
• Medium-chain fatty acids: 8-12 carbons
• Long-chain fatty acids: > 12 carbons

Fatty Acid Chain Length

• Chain length impacts a fatty acid’s chemical properties, physiological functions, and water solubility.

Saturation

• Saturated fatty acids feature single carbon-carbon bonds.
• Unsaturated fatty acids exhibit double bonds.
• Monounsaturated fatty acids contain one double bond.
• Polyunsaturated fatty acids have ≥2 double bonds.

Fatty Acid Nomenclature

• Alpha (α) Nomenclature: Based on double bond positions relative to the carboxylic (α) end.
• Omega (ω) Nomenclature: Categorizes fatty acids based on the first double bond relative to the methyl (ω) end, uses "n" system.

Double Bond Position

• For unsaturated fatty acids, abbreviations clarify double bond locations in molecules.
• In "C18: Δ9", the double bond starts at the 9th carbon from the carboxyl end.
• In the abbreviated form can written as C18: Δ9, 12, sometimes written as C18: 2Δ9, 12.
• If there is redundancy nbb bonds in fats are separated by a methylene group -C-.

Examples of Specific Fatty Acids

• Omega-3 fatty acid: The first double bond is between the 3rd and 4th carbons from the ω end.
• Omega-6 fatty acid: The first double bond is between the 6th and 7th carbons.

Double Bonds

• The number of double bonds influences a fatty acid's physical nature.
• Saturated fatty acids (SFA) are solid at room temperature.
• Monounsaturated (MSFA) are thick liquids or soft solids.
• Polyunsaturated (PSFA) are liquid.

Cis vs Trans

• Cis double bond: Hydrogen atoms are on the same side of the double bond.
• Trans double bond: Hydrogen atoms are on opposite sides of the double bond, resulting in the name being "Trans fatty acid"

Common Names

• Refer to the table for common names and food sources of important saturated and unsaturated fatty acids.

Naming fatty acids

• This includes Caproic (C6:0) - Caproyl. Caprylic (C8:0) - Caprylyl. Capric (C10:0) - Capryloyl. Lauric (C12:0) - Lauroyl. Myristic (C14:0) - Myristoyl. Palmitic (C16:0) - Palmitoyl. Palmitoleic (C16:∆9) - Palmitoleoly. Stearic(C18:0) - Steroyl. Oleic (C18:∆9) - Oleoyl. Linoleic(C18:∆9, 12) - Linoleoyl. Linolenic(C18:∆9, 12, 15) - Linolenoyl. Arachidonic(C20:∆5,8,11, 14) - Arachidonyl, DHA, and EPA.

Naturally Occuring Fatty Acids

• Double bonds in fatty acids usually have the cis configuration.
• Most naturally occurring fatty acids have an even number of carbon atoms.
• Examples: 14:0 myristic acid, 16:0 palmitic acid, 18:0 stearic acid, 18:1 cisΔ9 oleic acid, 18:2 cisΔ9,12 linoleic acid, 18:3 cisΔ9,12,15 α-linonenic acid, palmitoleic acid 16:1cisΔ9, 20:4 cisΔ5,8,11,14 arachidonic acid, 20:5 cisΔ5,8,11,14,17 eicosapentaenoic acid (an omega-3).

β-Oxidation of Fatty Acids

• Process releases energy from fatty acids

ATP Determination

• Process determines ATP yield from fatty acid beta oxidation.
• Example Formula: 17 + 17 + 17 + 12 – 2 = 61 ATP

ATP Formulas

• For even chains, ATPs produced = (17 * C – 10)/2 – 2 ATP.
• For odd chains, ATPs produced = [(17 * C – 51) + 6]/2 – 3.
• Remember to subtract 2 ATP if the C=C starts at an odd carbon, and 3 ATP if C=C starts at an even carbon

Beta Oxidations

• Where the fatty acid has an odd number of carbons. The last chop results in a three carbon molecule producing 6 ATPs. - 3 ATPs of activation energy.

Essential Fatty Acids

• The essential fatty acids for the diet are: Alpha-Linolenic acid (18:3) - ω-3 and Linoleic acid (18:2) - ω-6
• Cannot be synthesized by humans because lack desaturase enzymes.
• Used to created longer and more desaturated fatty acids.

Food

• Alaskan natives' diets high in ω-3 fatty acids from fish and marine mammals are related to enhanced physiological responses stimulated by ω-3 eicosanoids.

Sources of Essential Fatty Acids

• Linoleic acid: Nuts & seeds
• Linolenic acid: Oils (soybean, safflower, corn, flaxseed)
• EPA & DHA: Fatty fish & seafood
• Arachidonic acid: Variety of plant & animal foods

Essential Fatty Acid Deficiency

• Results in: Irritated & flaky skin, Gastrointestinal problems, Compromised immune system and Slow growth for children

SFA Guidelines

• Guidelines advise limiting saturated fatty acids.
• High intake correlates with cardiovascular disease risk.
• Dietary Guidelines for Americans suggest SFAs should be limited to no more than 10% of total kilocalories.

Trans Fat

• During partial hydrogenation, the process converts carbon-carbon double bonds found in PUFAs are converted to single bonds
• This forms trans fatty acids and reduces spoilage and improves texture.
• Food sources include shortening, margarine, crackers, pastries, and bakery products.
• Guidelines limit trans-fatty acid intake due to cardiovascular risks.
• The U.S. Dietary Guidelines recommend consuming less than 1% of kilocalories from trans fatty acids.
• Required on food labels from 2006>.

Mono-, Di-, & Triglycerides

• All are a Source of energy (ATP), insulation, protection
• Monoglycerides: Lipid is made of a glycerol bonded to 1 fatty acid
• Diglycerides: Lipid is made of a glycerol bonded to 2 fatty acids
• Triglycerides: Lipid is made of a glycerol bonded to 3 fatty acids

Triacylglycerols

• Triacylglycerols are are the simplest lipids where the 3 -OH groups of glycerol are each esterified to a fatty acid, unless all are the same, in “tripalmitin”, a name and position of each must be given

Functions of Triglycerides

• Provide body essential fatty acids.
• Is needed for Energy production, Insulation and Protection

Energy

• Adipocytes are specialized cells in adipose tissue used as an energy reserve
• Subcutaneous adipose tissue is found directly under the skin
• Visceral adipose tissue surrounds vital organs
• Large amounts of triglycerides can be stored as energy in a small space
• Lipids have Body has high energy yield
• Body has infinite ability to store excess energy in adipose tissue

Adipose

• Insulates the body and protects internal organs

Phospholipids

• Major components of cell membranes roles in digestion, absorption, transport of lipids, cellular metabolism
• Is both Amphipathic as it Contains both polar and nonpolar portions

Phosphatidate

Is the most basic phopholipid from which other other kinds are based

Glycerophospholipids

(phosphoglycerides), are common constituents of cellular membranes hydroxyls at C1 & C2 are Hydroxyls (OH) and esterfied to fatty acids

• An ester forms when a hydroxyl interacts with a carboxylic acids releasing water

Lipoproteins

Carry hydrophobic compounds

Sources

• Naturally found in most foods and is a Stabilizer to foods Mayonnaise & ice cream Soy products is Commenly called “lecithin”

Phospholipids & Mental Health

• Influences ability to think, speak, reason, remember & move and is Found and essential in neural development & function.