Y1S2 004 II Biochem Lipids Definition, Types, and Functions

Fatty Acids

• Fatty acids with no double bonds are saturated, carrying the maximum possible number of hydrogen atoms (Example: Stearic Acid)
• Fatty acids with at least one double bond are unsaturated, lacking hydrogen atoms (Example: Linoleic Acid)
• Cis fatty acids have hydrogen atoms on the same side of the double bond
• Trans fatty acids have hydrogen atoms on opposite sides of the double bond

Essential/Non-Essential Fatty Acids

• Non-essential fatty acids are produced by the body
• Essential fatty acids are derived from diets and are necessary for vital functions (Examples: Linoleic (C18:2 ω6) and α-Linolenic (C18:3 ω3))

Triglycerides

• Triglycerides are formed from a molecule of glycerol and three fatty acids
• Triglycerides are major components of VLDL and chylomicrons
• Triglycerides are important in metabolism as energy sources and transporters of dietary fat

Phospholipids

• Phospholipids contain one or more fatty acids attached to a phosphate and an alcohol
• Phospholipids may be attached to glycerol or sphingosine
• Phospholipids derived from glycerol are called phosphoglycerides

Lipids

• Lipids are a chemically diverse group of organic compounds, defined by their insolubility in water
• Lipids are highly soluble in non-polar solvents (Chloroform and ether)
• Lipids' water-insolubility contributes to the complexity in their digestion, transport, and metabolism

Types of Lipids

• Fatty acids are long hydrocarbon chains with various lengths and degrees of unsaturation, terminating with carboxylic acid groups
• Fatty acids' carbon atoms are numbered starting at the carboxyl terminus
• The systematic name is derived from the parent hydrocarbon's name, substituting "oic" for the final "e"
• Examples: octadecanoic acid (C18 saturated fatty acid), octadecenoic acid (C18 fatty acid with one double bond), cardiolipin (found in the heart), and sphingomyelin (found in the brain)

Glycolipids

• Glycolipids are sugar-containing lipids derived from sphingosine
• Glycolipids differ from sphingomyelin in the identity of the unit linked to the primary hydroxyl group of the sphingosine backbone
• Examples: cerebroside (simplest glycolipid, found in neural tissue, contains a sugar residue of glucose or galactose)

Sterol Lipids

• Cholesterol is built from 4 linked hydrocarbon rings, with a hydrocarbon tail linked to the steroid at one end and a hydroxyl group attached at the other end
• In membranes, the orientation of cholesterol is parallel to the fatty acid chains of phospholipids, and the hydroxyl group interacts with nearby phospholipid head groups
• Bile salts have the 4 linked hydrocarbon rings plus taurine, glycine, or both (example: originates from cholesterol)

Lipid Profile

• High-density lipoprotein cholesterol (HDL-C): >1.2mmol/l
• Low-density lipoprotein cholesterol (LDL-C): 2.4mmol/l
• Triglyceride