What are proteins?
Proteins are the most important biological molecules.
---> They are made up of the monomer, amino acids.
There are 20 amino acids in total.
Amino acids all have the same strucutre.
They have an amino group, a carboxyl group and a central carbon atom.
Each amino acid also has an R group. This group varies with each amino acid.
Two amino acids can form a peptide bond.
How it forms:-
1) The carboxyl group of one amino acid and the amino group of the other line up against each other.
2) This reacts and produces water - making this a condesation reaction.
Structures of Proteins
There are four main structures of proteins:-
!) Primary Structure - A long polypeptide change.
2) Secondary Structure - Interactions between amino acid chains cause chains to form in 3D sections. (e.g. the alpha helix and beta-pleated sheets).
3) Tertiary Structure - The overall (often completed) protein shape. (There are ionic, hydrogen an disulfide bonds.)
4) Quarternary Structure - Some proteins have more then one chain and the arrangement of those is the quartenary structure. (The many chains can be called subunits.)
Testing for Proteins
The Biuret Test
1) Place the sample to be tested in a test tube and add an equal volume of sodium hydroxide at room temperature.
2) Add a few drops of very dilute copper(ii) sulfate and mix gently.
3) A purple discolouration indicates the presence of peptide bonds, therefore a protein. No discolouration equals no protein.
Types of proteins
There are two types of proteins, fibrous and globular.
Fibrous - These are proteins formed by parallel polypeptide chains held together by crosslinks.
- Long, rope-like fibre.
- High tensile strength.
- Insoluble in water.
Examples include:- collagen (in skin'), keratin (nails, hair etc), silk.
Globular - Forms a spherical shape.
- Caused by tightly folded polypeptide chains.
Examples include:- Transport proteins (haemoglobin etc), Enzymes (e.g. lipase) and hormones (oestrogen, insulin etc).