Proteins are sort of polymers. They are made of polypeptide chains which are formed from amino acid monomer units. We need to know the structure of an amino acid:
NH2 represents the amine/amino group
COOH represents the carboxyl group
R represents the side chain/group - this is what differs in each amino acid (it is the variable part).
A functional protein often contains 3-4 polypeptide chains.
Proteins are formed from 3, often 4, structures. These are known as the primary, secondary, tertiary and quaternary structure.
- Amino acid sequence (polypeptide chain)
- This sequence is folded into a pleated sheet/alpha helix which is held together by the -NH and -C=O from amino acids (these really form hydrogen bonds twisting the chain)
- The pleated sheet/alpha helix is further folded into a specific tertiary structure which is bonded by disulphide bridges/ionic bonds/hydrogen bonds
- Potentially a number of individual polypeptide chains are linked in various ways. They may also be associated with prosthetic (non-protein) groups.
We can test for proteins using the biuret test:
Place a sample of the solution to be tested in a test tube
Add an equal volume of sodium hydrogen solution at room temperature
Add a few drops of dilute copper (2) sulphate solution
Mix gently
Purple = protein
Blue = no protein
No comments:
Post a Comment