BCM 3000 PRINCIPLES OF BIOCHEMISTRY (Semester 1 -2011/12)
LIPID • Learning outcome (Objectives) • Function and distribution. • Characteristics of fatty acids-structure and chemical properties. • Saturated and unsaturated fatty acids . • Structures and properties of phospholipids, sphingolipids, waxes, terpenes and steroids.
LIPID DEFINITION : General definition – all compounds called fat and oils TECHNICAL DEFINITION Fat : Triglycerides in the form of solids at room temperature Oils : Triglycerides which are liquid at room temperature
General Definition • Any natural compound which is insoluble or nearly insoluble in water but soluble in non-polar solvents – • Chloroform • CS2 • Ether • warm or • hot ethanol
FUNCTIONS Lipids are widely distributed in both animal and plant systems and perform a wide variety of functions • Structural functions - Components of membranes • Storage forms of carbon and energy • precursor for major compounds – e.g. hormones. • Insulators - thermal, electrical or physical shock • protective coatings – prevent infections, loss or addition of compounds • Regulators - as vitamins & hormones
CLASSIFICATION • 1. SIMPLE LIPIDS • Fatty acid esters • (Acid + alcohol ester) • 2. COMPPOUND LIPID • Fatty acid + alcohol + OTHER COMPOUNDS
SIMPLE LIPIDS ??? Esters
COMPOUND LIPIDS 4 types of Compound lipid i.Phosphoglycerides ii. Sphingolipids iii. Cerebrosides iv. Gangliosides
i & ii=Phospholipid - presence of phosphate ii , iii & iv =Sphingolipids - presence ofSphingosine iii & iv =glycolipid - presence ofcarbohydrate
GLYCEROL – Trihydroxy alcohol
FATTY ACIDS • Long chain aliphatic carboxylic acids- contains carboxyl group – polar head and `tail’ containing hydrocarbon chain • Amphiphilic compounds –hydrophilic head and hydrophobic tail • COOH can be ionised • Monocarboxyilic acids – linear hydrocarbon chain, even carbon numbers – between C12-C20 • Short, longer , branched, cyclic and odd numbers also exist BUT not many
FATTY ACIDS • 2 TYPES • Saturated Fatty acids • Unsaturated Fatty acids
Structure of Fatty Acids - Saturated • Fats • mostly from animal sources, • have all single bonds between the carbons in their fatty acid tails, thus all the carbons are also bonded to the maximum number of hydrogens possible. • saturated fats • The hydrocarbon chains in these fatty acids are, thus, fairly straight and can pack closely together, making these fatssolidat room temperature.
Saturated fatty acid –e.g. • palmitic acid (CH3(CH2)14COOH) (16C) & • Stearic acid (CH3(CH2)16COOH)
Structure of Fatty Acids - Unsaturated • Unsaturation normally at - C18 & C20 – double bond separated by methylene group -CH = CH - CH2 - CH = CH • Double bonds = cis configuration • Unsaturated fatty acid - oleic (18:1), Linoleic (18:2), Linolenic (18:3) & arachidonic (18:4)
Unsaturated fatty acids • C=C double bond arranged in two ways • In cis bonds, the two pieces of the carbon chain on either side of the double bond are either both “up” or both “down,” such that both are on the same side of the molecule • In trans bonds, the two pieces of the molecule are on opposite sides of the double bond, that is, one “up” and one “down” across from each other • Naturally-occurring unsaturated vegetable oils have almost all cis bonds, but using oil for frying causes some of the cis bonds to convert to trans bonds
fatty acids with trans bonds are carcinogenic, or cancer-causing. • containing products such as margarine are quite high,
Oils • mostly from plant sources, • have some double bonds between some of the carbons in the hydrocarbon tail, causing bends or “kinks” in the shape of the molecules. • Because some of the carbons share double bonds, they’re not bonded to as many hydrogens • oils are called unsaturated fats. • kinks unsaturated fats can’t pack as closely together, making them liquidat room temperature
Making margarine • Vegetable oils often contain high proportions of polyunsaturated and mono-unsaturated fats (oils) liquids at room temperature. • You can "harden" (raise the melting point of) the oil by hydrogenating it in the presence of a nickel catalyst.
SIMPLE LIPIDS • 2 GROUPS • Neutral acyglycerols (e.g. Triacylglycerol) • Waxes • Acyglycerols • = glyceride = atryhydroxy alcohol ester • = glycerol + fatty acid (3 different fatty acids) • = can be esterified
Glycerol= trihydroxy alcohol
Triacylglycerol – the most abundant • No ionic groups - neutral lipids • Triacylglycerol = neutral fats (solids) @ neutral oils (liquid)
FUNCTIONS IN ANIMALS • Adipose tissues - `fat depots' = storage forms of carbon and energy • II. Transport - chylomicrons - = lipoprotein – fatty acids are transported through lymphatic system and blood tissue adipose tissues and other organs • III. `Physical protection' - e.g. temperature.
WAXES • Also an ester - alcohol & fatty acid = very long hydrocarbon chain – commercial application • hairs, skin, leaves, fruits
WAXES Asid Oleic
CHEMICAL CHARACTERISTICS OF TRYACYLGLYCEROL (Reactions of Triacylglycerol) 1. Hydrogenation
Double bonds in vegetable oils can be hydrogenated oils become solids – can control - e.g.. peanut butter - crunchy, creamy HYDROGENATION PROCESS