Step-by-step explanation:
proteins are made up of 21 different L-amino acids. these amino acids are joined together with peptide bonds. peptide bond is a bond between a caboxylic group of one amino acid with amino group of other amino acid.
following is a figure to describe the structure of a single amino acid, where R -group is variable and can contribute for the amino acid to be neutral, acidic or basic. next figure gives an idea of how many various amino acids are there.