9701 · 34.4
Amino acids — FAQ
Frequently asked questions for 9701 Amino acids. Direct answers first, then deeper explanation — then practise with marking.
Why are they called 'alpha' (α) amino acids?
Because the amine group (–NH₂) is attached to the alpha-carbon, which is the first carbon atom immediately adjacent to the carboxyl (–COOH) functional group.
What is the difference between a peptide, a polypeptide, and a protein?
A peptide is a short chain of amino acids. A dipeptide has two, a tripeptide has three. A polypeptide is a long, continuous, unbranched chain of amino acids. A protein consists of one or more polypeptides that have been folded and coiled into a specific three-dimensional structure.
How does electrophoresis separate amino acids?
A mixture of amino acids is placed on a support medium (like paper or gel) buffered to a specific pH, and an electric field is applied. At a pH below its pI, an amino acid is positively charged and moves towards the negative electrode (cathode). At a pH above its pI, it is negatively charged and moves towards the positive electrode (anode). An amino acid at its pI is neutral (a zwitterion) and does not move. This allows for separation based on charge.
Are the L- and D- forms of amino acids equally common in nature?
No. While both enantiomers are chemically possible, virtually all proteins in living organisms are made exclusively from L-amino acids. This is an example of stereospecificity in biological systems.