Lecture 22_Lipid introduction.pdf

PBBS508 Biochemistry and Genetics Lecture Note 2024 Lecture 22: Lipid metabolism: Digestion and Absorption Lipids are heterogenous groups of organic molecules, being non-polar (hydrophobic) or amphipathic (having both hydrophobic and hydrophilic properties). Functions of Lipids: 1. Major sour...

PBBS508 Biochemistry and Genetics Lecture Note 2024 Lecture 22: Lipid metabolism: Digestion and Absorption Lipids are heterogenous groups of organic molecules, being non-polar (hydrophobic) or amphipathic (having both hydrophobic and hydrophilic properties). Functions of Lipids: 1. Major source of energy: fuel Storage (TAGs) 2. Important component of biological membranes (phospholipids, glycolipids, cholesterol) 3. Hormone: important for communication between cells (steroid hormones and eicosanoids) 4. Solubilization of non-polar substances in body fluids (fat soluble vitamin) Types of Lipids in humans (detail in the handout) Fatty acids, Triacylglycerols (TAGs), Phospholipids (glycerophospholipids, sphingolipids), Eicosanoids, Steroids, Complex lipids (lipoproteins, glycolipids), Fat soluble vitamins Fatty acid structure and nomenclature Fatty acids consist of carboxyl group, which make it hydrophilic, and hydrocarbon chain part, which make it hydrophobic. Most fatty acids in our body have 16, 18, and 20 carbon atoms. The fatty acids with some double bonds, with a kinking structure are known as unsaturated fatty acids. The fatty acids with no double bond are known as saturated fatty acids. Fatty acid is essential for our body in terms of providing energy and maintaining normal cell structure. Fatty acids can be intake from diets and de novo synthesis by our body. There are 4 ways to call fatty acids - Trivial nomenclature: the name that derived from the source of fatty acids where it was first isolated i.e., palmitic acids (from palm oil), oleic acids (from olive oil). - IUPAC nomenclature: the Greek derived nomenclature is included to tell the length of the chain, the double bond positions are also stated in front of Greek name (given carboxyl carbon the number one carbon of the chain i.e., 9,12,15 octadecenoic acids (linolenic acid) - Carboxyl nomenclature: carboxyl reference system tells number of carbons: number of double bonds and the position of them i.e., 18:3 9, 12, 15 (linolenic acid) - Omega nomenclature: omega reference tells the number of carbons: number of double bonds and the closest position of double bond count from omega carbon (methyl carbon) i.e., 18:3 (omega-3) Different types of fatty acids (based on number of carbon) Short-chain fatty acids (< 6 carbons), Medium-chain fatty acids (6-12 carbons), Long-chain fatty acids (13-20 carbons), Very long-chain fatty acids (21 or longer carbons) (Note: exact number might be different). PBBS508 Biochemistry and Genetics Lecture Note 2024 Digestion and absorption of dietary lipid 90% of lipids in high-fat meal is triacylglycerol (TAG) and 10% are cholesterol, cholesterol esters, phospholipids and free fatty acids. Linoleic and linolenic acids which are essential lipids (the body cannot synthesize). Due to water insoluble nature of lipids, fat is present in chyme as lipid droplets. Digestion of Lipids 1. Digestion of lipids start in mouth and then stomach by acid-stable lipases (Lingual lipase and gastric lipase) which digest only triacylglycerol (TAG) with short and medium chain FA (