polypeptide chain (proteins and aminoacids )

QUALITATIVE ANALYSIS OF AMINO ACIDS AND PROTEINS:
Proteins : are large biological molecules, or macromolecules, consisting of one or more chains of amino acid residues. Proteins perform a vast array of functions within living organisms, including catalyzing metabolic reactions, replicating DNA, responding to stimuli, and transporting molecules from one location to another. Proteins differ from one another primarily in their sequence of amino acids, which is dictated by the nucleotide sequence of their genes, and which usually results in folding of the protein into a specific three-dimensional structure that determines its activity .
Amino acids are molecules containing an amine group, a carboxylic acid group and a side chain that
varies between different amino acids. Amino acids of the general formula RCH(NH2)COOH are
amphoteric, behaving as amines in some reactions and as carboxylic acids in others. At a certain pH
known as the isoelectric point an amino acid has no overall charge, since the number of protonated
ammonium groups (positive charges) and deprotonated carboxylate groups (negative charges) are
equal. Since the amino acids at their isoelectric points have both negative and positive charges, they
are known as zwitterions.