Proteins are the most abundant intracellular macro molecules. These constitute more than half of dry weight of most organisms. Some proteins provide structural elements of the body such as hairs, collagens, enzymes are oxygen carriers.
There are 100,000 kinds of proteins in humans. They are most important for cell functions. Proteins are the linear polymers of 20 amino acids. The amino acids differ from each other in having different R-groups. The R-groups may be changed. They may be polar, non-polar, aromatic or hydrophobic. Amino acid sequences in different proteins differ. This difference is due to diversity in R-groups of 20 amino acids. Their specific location and functions are given in Table. Proteins are grouped into different types on the basis of their biological functions
