lipids

• • 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

• 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
• mono-unsaturated
• If the hydrocarbon chain contains several double bonds, the fatty
• acid is poly-unsaturated.

• • 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 fats
  often 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.
• BUT
• • 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 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

• • 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 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 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"

• – 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