LIPIDS I

Definition: Made up of C, H and O Lipids are hydrophobic compounds. insoluble or poorly soluble in water, Readily soluble in non-polar solvents such as ( ether, benzene, acetone, chloroform)

Biological Functions of Lipids As a major source of energy, lipids provide 9 kcal of energy per gram Triglycerides provide energy storage in adipocytes Phosphoglycerides, sphingolipids, and steroids are structural components of cell membranes Steroid hormones are critical intercellular messengers Fat-soluble vitamins (A, E, D, K) Dietary fat acts as a carrier of Fat-soluble vitamins into cells of small intestine Fat stored in adipose tissue serves as thermal insulator in the subcutaneous tissue and protective around certain organs (e.g. kidney).

Lipids act as electrical insulators in myelinated nerves to allow rapid propagation of nerve impulses. Cholesterol is an important constituent of the cell membrane and is essential for the synthesis of steroid hormones, bile acids and vitamin D. Fat-soluble vitamins, steroid hormones and eicosanoids play important regulatory roles in the body.

Lipoproteins (e.g. LDL & HDL) are a mean for transporting lipids in blood. Imbalance in lipid metabolism can lead to major clinical problems such as obesity and atherosclerosis

Test your understanding 1- All of the following are true about lipids except: They are energy source They are soluble in water They are hydrophobic compounds Serve as thermal insulators Structural components of cell membranes 2- Lipids share the property of being: Soluble in water. Soluble in organic solvents. Insoluble in water. Insoluble in organic solvents. Both b and c.

Test your understanding 3- Lipids are considered as: First source of energy in the body. Second source of energy. Third source of energy. Energy reserves in the body. Both b and d.

Fatty Acids Fatty acids are water-insoluble. Long straight-chain carboxylic acids no branching Most common chains range from 10–20 carbons in length Can be saturated (containing no double bonds) or unsaturated (containing one or more double bonds that are always separated at 3 carbon intervals), but usually no other functional groups present The general formula of saturated fatty acids is: CH3 - ( CH2)n – COOH Any fatty acid that cannot be synthesized by the body is called an essential fatty acid

Fatty Acid Nomenclature Nomenclature reflects location of double bonds also used are common names (e.g., oleic, stearic, palmitic)

Carbon atoms in a fatty acid are numbered by 2 different systems: Beginning from the carboxyl carbon (Δ delta end) as carbon 1, where numeric designation of the fatty acid shows the number of carbon atoms 2- followed by the number of double bonds, 3- then the site of unsaturation. 4 2 16 1 3 15 COOH

Palmitic acid: CH3(CH2)14COOH ; 16:0 (16:0 indicates a fatty acid with 16 carbons and no double bonds). Oleic acid: CH3(CH2)7C=C(CH2)7COOH ; 18:1 Δ 9 (18:1 Δ 9 indicates a fatty acid with 18 carbons and one double bond between carbons 9 and 10).

Linoleic acid: CH3 (CH2) 4C=CCH2C=C(CH2) 7COOH ; 18:2 Δ 9,12 (18:2 Δ 9,12 indicates a fatty acid with 18 carbons and 2 double bonds between carbons 9 and 10 and carbons 12 and13). Linolenic acid: CH3CH2C=CCH2C=CCH2C=C(CH2) 7COOH; 18:3 Δ 9,12,15 (18:3 Δ 9,12,15 indicates a fatty acid with 18 carbons and 3 double bonds between carbons 9 and 10, carbons 12 and 13 and carbons 15 and 16).

Arachidonic acid: CH3 (CH2) 3(CH2C=C) 4(CH2) 3COOH; 20:4 Δ 5,8,11,14 (20:4 Δ 5,8,11,14 indicates a fatty acid with 20 carbons and 4 double bonds between carbons 5 and 6, carbons 8 and 9, carbons 11 and 12 and carbons 14 and 15).

2. Beginning with the terminal methyl carbon (known as omega ώ carbon) as carbon 1, where ώ-3 for example indicates that; The closest double bond to the terminal methyl group begins after 3 carbons from that end. Therefore, linoleic acid ; is an ώ -6 fatty acid CH3 (CH2) 4C=CCH2C=C(CH2) 7COOH ώ -6,18:2 Δ 9,12 linolenic acid ;is an ώ -3 fatty acid. CH3CH2C=CCH2C=CCH2C=C(CH2) 7COOH ώ -3,18:3Δ9,12,15

Fatty Acid Properties Melting point increases with increasing carbon number Melting point of a saturated fatty acid is higher than an unsaturated fatty acid with the same number of carbons Typical saturated fatty acids are tightly packed together cis double bonds prevent good alignment of molecules in unsaturated fatty acids leading to poor packing Double bonds lower melting point relative to saturated acid

Common Fatty Acids

Saturated & Unsaturated Fatty Acids A. Saturated Fatty Acids: No of Double Bonds No of Carbon Atoms Name 12 Lauric (12:0) 14 Myristic (14:0) 16 Palmitic (16:0) 18 Stearic (18:0) Saturated fatty acids do not have double bonds. They are formed inside the body.

Saturated Fatty Acids Octanoic Acid

B. Unsaturated Fatty Acids: No of Double Bonds No of Carbon Atoms Name 1 16 Palmitoleic (16:1) 18 Oleic (18:1) 2 Linoleic (18:2) 3 Linolenic (18:3) 4 20 Arachidonic (20:4) The first double bond is usually at the ninth carbon The double bond is normally in a cis configuration Double bonds lower the melting temperature The cis configuration doesn’t allow fatty acids to pack as close together

Saturated vs. Unsaturated Fatty Acids saturated: the SFA’s of a lipid have no double bonds between carbons in chain polyunsaturated: more than one double bond in the chain most common polyunsaturated fats contain the polyunsaturated fatty acids (PUFAs) oleic, linoleic and linolenic acid unsaturated fats have lower melting points stearic (SFA) melts at 70oC, oleic (PUFA) at 26oC

Unsaturated fatty acids have one or more double bonds Unsaturated fatty acids have one or more double bonds. There are 2 types: Essential fatty acids: These fatty acids are with more than one double bond, e.g. linoleic, linolenic and arachidonic, they are not formed in the body and should be obtained from the diet. Non-essential fatty acids: These can be synthesized in the body.

Unsaturated Fatty Acids 3 - Octenoic Acid 3, 6 - Octadienoic Acid Short hand: 8:1 (D3) 8:2 (D3,6)

Polyunsaturated Fatty Acids Linoleic acid: Cis, cis, 9, 12 - Octadecadienoic acid Linolenic acid: Cis, cis, cis 9, 12, 15 - Octadecatrienoic acid Arachidonic acid: Cis, cis, cis, cis 5, 8, 11, 14 - Eicosatetraenoic acid   Linoleic Acid Linolenic Acid Arachidonic Acid

Saturated vs. Unsaturated Fats saturated fats tightly packed, clog arteries as atherosclerosis because of double bonds, polyunsaturated fats do not pack well -- like building a wall with bricks vs. irregular-shaped objects plant fats are much higher in PUFA’s than animal fats

Cis And Trans Fatty Acids Cis 9 - Octadecenoic Acid (oleic) Trans 9 - Octadecenoic Acid (elaidic acid)

Naturally-occurring fatty acids 1. Cis form 2. Not conjugated --- isolated double bond. 3. Even numbered fatty acids.