Medical Biochemistry (2) Level 2 Part II (Lipids) week 3 Taif University College of Medicine Preparatory Year Students

Lipids

Lectures outlines Definition and importance of lipids Classification of lipids Fatty acids structure and properties Important reactions of FA Glycerides Non-glyceride lipids Membranes Lipids

What are lipids?

Definition A collection of organic molecules of varying chemical composition. They are grouped together on the basis of their solubility in nonpolar solvents. They are widely distributed in nature both in plants and in animals.

The great structural diversity among lipids The defining parameter for lipids is solubility rather than structure.

What are the Biological Functions of Lipids?

Biological functions of lipids Energy source (Fatty acids) Energy storage (triacylglycerols) Structural components of cell membrane (phospholipids, sphingoglycolipids, and cholesterol) Hormones (steroid hormones) Emulsifiers (Bile salts) Protection and insulation (biological waxes) Source of Fat-soluble Vitamins.

What are the main Classes of Lipids?

Classification of Lipids 1.Simple lipids (Fats & Waxes) 2.Compound or conjugated lipids 3.Derived Lipids 4.Lipid-associating substances(Fat soluble vitamins,pigments,etc)

Lipids Classification Eicosanoides

What are the general structure of fatty acids?

Fatty Acids Usual fatty acids are unbranched Aliphatic carboxylic acids polar Hydrophilic Head Nonpolar Hydrophobic Tail SaturatedUnsaturated R have carbon-carbon double bonds without double bonds

Fatty Acids  Most naturally occurring fatty acids have a chain of an even number of carbon atoms, from 4 to 28.  Fatty acids are usually derived from triglycerides or phospholipids.  When they are not attached to other molecules, they are known as "free" fatty acids.  Fatty acids are important sources of fuel because they yield large quantities of ATP.  Many cell types can use either glucose or fatty acids for this purpose. In particular, heart and skeletal muscle prefer fatty acids.

Length of free fatty acid chains aliphatic tails < 6 carbonsShort-chain fatty acids (SCFA) aliphatic tails 6-12 carbonsMedium-chain fatty acids (MCFA) aliphatic tails carbonsLong-chain fatty acids (LCFA) aliphatic tails > 23 carbonsVery long chain fatty acids (VLCFA) Fatty acid chains differ by length, often categorized as short to very long.

Fatty Acids Common fatty acids

Fatty Acids Fatty acids

Fatty Acids Cis Fatty Acids Unsaturated fatty acids Trans fatty acid

Fatty Acids Delta (  )Omega (  ) Numbering -COOH -CH3-COOH-CH3 18:2  9,12 18:2  6,9 Linoleic acid 18:

Omega-3 & Omega-6 fatty acids

Nomenclature Stearic acid are non-systematic historical names, which are the most frequent naming system used in literature Trivial nomenclature (or common names) octadecanoic acid derive from the standard IUPAC Rules for the Nomenclature of Organic Chemistry Systematic nomenclature (IUPAC names) 18:2  9,12 the location of the double, counting from the carboxylic acid end. Δ x nomenclature (or delta-x) 18:2  6,9 the location of the double, counting from the terminal methyl carbon ω x nomenclature (or omega –x) Lipid numbers take the form C:D where: C = the number of carbon atoms and D = the number of double bonds in the fatty acid

Essential fatty acids Fatty acids that are required by the human body but cannot be made from other substrates, and therefore must be obtained from food. There are two essential fatty acids: – Linoleic acid and – Linolenic acid. These two acids: – (1) are needed for proper membrane structure and – (2) serve as starting materials for the production of several nutritionally important longer-chain omega-6 and omega-3 acids

Classification Scheme for Fatty (summary) acids PUFAMUFA

Questions What are the differences between saturated and unsaturated fatty acids? Write the chemical structure, the delta and the omega number of the following fatty acids: PalmiticStearic PalmitoleicOleic LinoleicLinolenic