Biological molecules - Lipids Flashcards
What are lipids?
They are biological molecules made of carbon, hydrogen and oxygen which are only soluble in organic solvents such as alcohols.
The main lipid types are triglycerides and phospholipids.
What are triglycerides?
They are formed by the condensation reaction of one molecule of glycerol and three molecules of fatty acid, forming ester bonds
What are saturated lipids?
Don’t contain any carbon-carbon double bonds
Like those found in animal fats
What are unsaturated lipids?
Do contain carbon-carbon double bonds.
The presence of a double bond means that the molecule is able to bend.
As a result unsaturated fats cannot pack together as tightly and are therefore liquid at room temperature.
Can be found in plants
How does triglyceride structure relate to their function?
High ratio of energy storing carbon-hydrogen bonds to carbon atoms = excellent energy store.
A low mass to energy ratio = good storage molecule, with a lot of energy being stored in a small volume. This is beneficial for animals as it is less mass to move
around.
Being large and non-polar lipids are insoluble in water = their storage does not affect the water potential of cells.
A high ratio of hydrogen-oxygen atoms means that triglycerides release water when they are
oxidised = provide and important source of water for organisms to live in dry environments.
What is the structure of a phospholipid?
One of the fatty acids of a triglyceride is substituted by a phosphate- containing group.
Phosphate heads are hydrophilic and the tails are hydrophobic and as a result phospholipids form micelles when they are in contact with water.
The molecule is therefore known as polar
How does phospholipid structure relate to their function?
In an aqueous environment being polar means a bilayer can be formed.
The hydrophilic heads of the phospholipids can be used to hold at the surface of the cell surface membrane.
Their structure allows them to form glycolipds with carbohydrates which are important on the
cell surface membrane for cell recognition.
How do you test for lipids?
Emulsion test.
Take a completely grease free test tube and add 2cm^3 of the sample to be tested and 5cm^3 of ethanol.
Shake the test tube thoroughly to dissolve all the lipid in the solution.
Add 5cm3 of water and shake gently.
A cloudy-white colour indicates the presence of a lipid.
As a control repeat the experiment using water as the sample, the final solution should remain clear.
