3.1.3 Lipids

Name the 2 groups of lipids

Triglycerides and Phospholipids

What are lipids soluble in?

Only organic solvents like alchohols

How are Triglycerides formed?

The condensation of one molecule of glycerol (-OH) and three molecules of fatty acid (-COOH), forming 3 ester bonds and releasing 3 H2O molecules

What functional group does a fatty acid have?

-COOH (Carboxyl) functional group

How can a fatty acid vary? (3)

1- Chain length

2- Presence of double bonds; saturated (no double C-C bond) or unsaturated (double C=C bond)

3- Number of double bonds

How can you recognise a saturated lipid?

ONLY C-C single bonds, usually animal fats

How can you recognise an unsaturated lipid?

Contains C=C double bond(s), usually in plants

What does a double C=C bond do to the lipid?

The molecule is able to bend, unsaturated fats CANNOT pack together as compact and are LIQUID at room temp.

How can UNSATURATED lipids further vary?

They can be CIS-unsaturated (Hs on the same side of the C=C) or TRANS-unsaturated (Hs on opposite sides around C=C)

Properties of Triglycerides (4)

1) High ratio of energy storage carbon-hydrogen bonds to carbon atoms - good energy store

2) Low mass to energy ratio - lots of energy stored in smaller volume so less mass to move

3) Large and NON-Polar - insoluble in water so doesnt affect water potential

4) High ratio of hydrogen-oxygen atoms means triglycerides release H2O when oxidised - provide important source of water for dry environment organisms

How is a phospholipid formed?

One of the fatty acids of a triglyceride is substituted by a phosphate group

Why are phospholipids polar?

Phosphate heads (phosphate group) are hydrophillic and the tails are hydrophobic (fatty acid) so form micelles in contact with water

State the difference between triglycerides and phospholipids

Triglycerides have 1 glycerol and 3 fatty acids wherease Phospholipids have 1 glycerol, 2 fatty acids and 1 PHOSPHATE group

Properties of Phospholipids (3)

1) A bilayer can be formed in acqueous environment

2) Hydrophilic heads can be used to hold at the surface of the cell surface membrane

3) Can form glycolipids with carbohydrates which are important on cell surface membrane for cell recognition

Describe the test for lipids

EMULSION TEST:
1) Put 2cm^3 of the sample in a clean test tube
2) Add 5cm^3 of ethanol and shake thoroughly to dissolve sample
3) Add 5cm^3 of water and shake gently
=CLOUDY WHITE EMULSION indicated a lipid is present