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- • Lipids can be broadly classified as biomolecules which are insoluble in water – they contain a high percentage of non-polar hydrocarbon regions.
- • They exists as colloidal suspensions within the aqueous fluid of the organism
- • They are responsible for long term energy storage, building cell membranes, emulsification ofnutrients and protection of internal organs.
- • They can be further classified as – fatty acid derived (waxes, fats, prostaglandins) – steroids
Long hydrocarbon chain (10-20 C atoms, non-polar, water insoluble
- If the hydrocabon chain contains all single bonds, then the fatty acid
- is saturated
- If the hydrocarbon chain contains a double bond, the fatty acid is
- If the hydrocarbon chain contains several double bonds, the fatty
- acid is poly-unsaturated.
Fats and Oils
Fats are solids, Oils are liquid
- • Consist of triglycerol backbone and three fatty acids linked through oxygen atoms
- • Fats – Saturated- all C-C bonds are single bonded.
- • These type of fats contain the maximum of H atoms possible per carbon atom (the carbons are filled, or ‘saturated’ with H atoms – Unsaturated – some of the carbon atoms are joined with double bonds.
- • In principle, more H atoms can be added to these C atoms
- • The more double bonds (unsaturation) in the chain, the lower the melting point
- – saturated fatsoften solid at room temp.
- – mono unsaturated liquid at room temp, but will solidify in refrigerator
- – poly unsaturated lowest melting points saturated fats can "pack" efficiently
- into a crystal structure cis double bonds make 'packing' inefficientdifficult to crystallize into solids. Therefore they remain liquid at room temp. • Cis double bonds predominate
- • Humans can synthesize most fatty acids from carbohydrate feed stocks.
- • Polyunsaturated acids are inefficiently synthesized
- – obtained from external food sources
- – referred to as "essential fatty acids"
Omega-3 acids inhibit clotting of platelets in blood vessels, thereby perhaps providing protection against coronary disease.
Fats and Oils
- Fats and oils are the product of the reaction glycerol
- with fatty acids
- Fats are solids, while oils are liquids
- Fats are also known as triglycerides
- Fats are used by organisms for long term storage of energy
Partially Hydrogenated Fats
- • Formed by treating polyunsaturated vegetable fats with hydrogen
- • Advantages
- – Proper consistency for use as margarine and shortenings
- – More resistant to oxidation and spoilage
- • Disadvantages
- – Formation of saturated fats bad cholesterol
- – Formation of trans fatty acids. bad cholesterol
- Unsaturated fats have cis double bonds.
- Trans-fatty acids are implicated in the formation of LDL cholesterol\
- The hydrogenation process often leads to the formation of transfatty acids as an unwanted by-product
- • Heating a fat with a strong base breaks the ester bonds
- • The result is a sodium salt of the fatty acid
- • These are called ‘soaps’
- – hydrophobic chain (dissolves greasy matter)
- – hydrophilic CO -Na+ end mixes with water 2
- – results in dispersing of greasy matter (dirt) in water
- •Key points:
- –they are consist of a glycerol backbone, two fatty acid chains and 1 ester of phosphoric acid and amino alcohol
- – They contain a nonpolar region (fatty acid chain) and highly polar region (ionized nitrogen)
- – most abundant lipid in cell membranes (walls).
- – they assist in making cell membranes permeable so that molecules can enter and leave the cell
Steroids are characterized by 4 ring system- 3 rings have 6 carbon atoms each (A-C); the D ring has 5 carbon atoms
- Hormones are chemical messengers that signal between different cell types within the progesterone
- (signals uterus prior to implantation of fertilized egg) norethindrone (contraceptive) organism.
(Cholesterol and Steroid Hormones)
- • Cholesterol is essential for animal life
- – component of cellular membranes, myelin (nerve covering), brain and liver tissue
- – precursor (starting material) for Vitamin A
- – precursor for other hormones
- • Obtained via diet or synthesis in the liver
- – Diet
- • animal products only (not present in plants)
- – Synthesis in the liver
- • from carbohydrates
- • from fats (esp. saturated)
Transport of Cholesterol
LDL (low density lipoprotein)
- – Transport to cells for membrane synthesis, steroid hormones and bile salts.
- – If more LDL present than is needed for cell maintenance, LDL deposits cholesterol in lining of arteries heart disease, high blood pressure
- – "bad cholesterol"
Transport of Cholesterol
• HDL (high density lipoprotein)
- – function to pick up excess cholesterol and return it to the liver for breakdown and excretion.
- – "good cholesterol"
- • Recommended levels
- – Total: <200mg/dL
- – LDL: <130 mg/dL
- – HDL: >40mg/dL