KEGS Biology Blog


Wednesday 10th October Section 2
October 10, 2012, 8:19 am
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Lipids and Phospholipids

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Lipids in living organisms:
– energy source
– energy storage
– insulation
– mechanical protection
– buoyancy
– source of metabolic water

– Lipids make up around 5% of a cell’s organic matter.
– At room temperature (25°C), a solid lipid is called a fat and a liquid lipid is called an oil.
– In general, fats are found in animals whereas oils are found in plants.
– All lipids are insoluble in water and are substances rich in energy.

Glycerol and fatty acids
– Found in all the fats and oils which perform roles in energy storage and supply, and those found in membranes.
– Glycerol is always the same but fatty acids in lipids can differ significantly.
– Animals cannot make some of the fatty acids they need from raw materials taken into their bodies- these are called essential fatty acids, and must be taken in ‘complete’ as part of the diet.

Fatty acids
– All have an acid group at one end- one carbon with a single bond to an OH molecule and a double bond to an oxygen molecule.
– The rest of the molecule consists of a hydrocarbon chain (the fatty group) which can be anything from 2 to 20 carbons long. Instead of writing the whole chain out, it can be notated in a simpler form (a zigzag).

Saturated or unsaturated
– Saturated fatty acids are molecules which have a hydrocarbon chain saturated with hydrogen.
– Unsaturated fatty acids have C=C bonds, so fewer hydrogen atoms can be bonded to the molecule. One C=C double bond gives a mono-unsaturated fatty acid, two or more C=C double bonds give a polyunsaturated fatty acid.
– C=C double bonds change the shape of the hydrocarbon chain, which makes the molecules push apart and so makes them more fluid. This means that lipids containing a lot of unsaturated fatty acids are usually oils.

Triglycerides
– One glycerol molecule bonded to three fatty acid molecules.
– A condensation reaction between the acid group of a fatty acid molecule and one of the OH (hydroxyl) groups of the glycerol molecule forms a covalent bond, which is called an ester bond. A water molecule is also produced.
– The new molecule produced is a monoglyceride.
– A condensation reaction between acid groups of two or more fatty acid molecules with the two remaining OH groups on the glycerol forms a triglyceride molecule.
– Triglyceride molecules are insoluble i.e. hydrophobic.

Phospholipids
– Almost identical to triglycerides.
– A phospholipid molecule consists of a glycerol molecule with fatty acid molecules bonded by condensation reactions to produce ester bonds.
– In phospholipids, the 3rd fatty acid is replaced by a phosphate group, which is covalently bonded to the third OH group on the glycerol through a condensation reaction.
– The phosphate ‘head’ is hydrophilic and polar, but the hydrocarbon chain fatty acid ‘tails’ are hydrophobic and non-polar.
– The majority of the phospholipid molecule is insoluble in water, but the ‘water-loving’ head means that phospholipids are able to form membranes.
– Phospholipids arrange themselves into a bilayer with heads outside and tails inside.

Comment by sarahroche12

http://www.anyvitamins.com/fats-info.htm
Good website, both for this topic butwith links at the bottom to other relevant things i.e. carbohydrates and saccherides.

Comment by elliswhyte




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