"Each of the 20 amino acids has a central carbon atom with four covalent bonds. These bonds link the carbon atom to an amino group ( NH2 ), a carboxyl group ( COOH ), a hydrogen atom, and an R group. The R group can be a carbon side chain, a hydrogen atom, or a functional group. " -------- from my textbook.
The correct option is ANALOGOUS STRUCTURES. Analogous structures are structures that are similar because of the functions they carry out and because of their external appearance. But these structures are different internally.<span />
