KEGS Biology Blog

Wednesday 10th October Section 2
October 10, 2012, 8:19 am
Filed under: Uncategorized

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.

– 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.

– 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
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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