Biological Molecules Topic Write Up


Water

Water is made up of two Hydrogen molecules and one Oxygen molecule. As a liquid, water is constantly making and breaking Hydrogen bonds.

Sugar
Carbohydrates refers to a group of molecules containing Carbon, Hydrogen, Oxygen. Carbohydrates are 'Hydrated Carbon' which means that for every Carbon their are two Hydrogens and one Oxygen.

Functions of Carbohydrates:


Monosaccharides are the simplest carbohydrates. They have a large number of Carbon-Hydrogen bonds, making them a good source of energy.

Disaccharides are two monosaccharides combined. They are bonded by a glycocidic bond, formed in a condensation reaction. In a condensation reaction, water is expelled. Disaccharides can be broken down into monosaccharides by a hydrolysis reaction which requires the addition of water. The water provides a hydroxyl group (-OH) and a Hydrogen which helos the glycosidic bond to break.

Polysaccharides are three or more monosaccharides combined. They can be made up of hundreds or thousands of monosaccharides. Polysaccharides are good energy stores, because they are compact, and they are made up of chains (so can easily be 'snipped off' when needed for respiration).


Triglycerides
Triglycerides are made up of glycerol and three fatty acids bonded together through a condensation reaction. This reaction creates an ester bond between the -COOH group and the -OH groups.

Glycerol is an alcohol (it has free -OH groups), made up of three carbon atoms and three -OH groups.

Fatty acids are the building blocks of fat. They contain a carboxyl group (-COOH) on one end which is attached to a hydrocarbon tail (A long chain of Carbon and Hydrogen atoms). Fatty acids are acidic, because the carboxyl group ionises into a H+ and -COO- group. We say a fatty acid is saturated if it has a Carbon double bond, and unsaturated if not. A saturated fatty acid has a structural kink where the double bond is.

Functions of triglycerides:




Proteins


Testing for Carbohydrates

Starch
Add iodine to sample. Solution will turn from yellow to blue if starch is present

Reducing Sugars
Heat sample with Benedict's solution. Solution will turn from blue to green to yellow to orange to red if reducing sugar is present

Non-reducing Sugars
Test sample for reducing sugars to ensure none are present. Take separate sample and boil with HCL. Cool solution and use sodium hydrocarbonate to neutralise it. Test for reducing sugars again.

Lipids
Mix sample with ethanol. Filter. Pour solution into water. Cloudy white emulsion indicates presence of lipids

Proteins
Add biuret solution to sample. Lilac colour indicated presence of proteins.