<span>Amino acids are the basic structural unit of all proteins. A 'free' amino acid (a single amino acid) always has:
an amino group -NH2,
a carboxyl group -COOH
a hydrogen -H
a chemical group or side chain -"R".
Since the amino acids (except glycine) have 4 different groups attached to the a-carbon, they are optically active stereoisomers (recall 23.101 Organic Chemistry) although only L-isomers are found in proteins.
At a neutral pH, both the amino and the carboxyl groups are ionised, giving what is termed the zwitterionic</span>
It is defiantly not A, neither B, I'm thinking either C or D but I think it's C
Endorphins are brain chemicals
known as neurotransmitters which are released when the body feels a certain
amount of stress and pain. Endorphins alter the communication of pain in the
body by interacting with the opiate receptors and blocking the synapse so that signals
cannot be sent to the brain in order to reduce an individual perception of pain.
