AQA Chem4: Amino Acids Revision notes on amino acids from the organic section of AQA Chem4 3.0 / 5 based on 1 rating ? ChemistryAcids, bases and saltsA2/A-levelAQA Created by: annaCreated on: 06-06-13 10:37 Amino Acids there are 20 important naturally occuring amino acids all amino acids have two functional groups, an amine -NH2 and a carboxylic acid -COOH a typical amino acid is a white crystalline solid with a melting point of 200C they can exist as zwitterions which are ions with a permanent positive and negative charge but which are neutral overall, these charges mean they can pack together as an ionic lattice in acidic conditions the carboxylic acid part is protonated so the molcule has an overall positive charge in basic conditions the amino group is deprotonated so the molecule has an overall negative charge 1 of 2 Peptides, Polypeptides and Proteins amino acids link together to form peptides molecules containing up to about 50 amino acids are referred to as polypeptides when there are more than 50 amino acids they are proteins the amine group of one amino acid will react with the carboxylic acid of another to give an amide or peptide linkage compounds formed by the linkage of 2 amino acids are called dipeptides and those formed by the linkage of 3 amino acids are tripeptides you can use hydrolysis to break down a polypeptide into the individual amino acids to separate a mixture of amino acids you can use column chromatography and to identify the different amino acids you can use paper chromatography proteins have complex shapes which are held in place by hydrogen bonds 2 of 2
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