Choose the correct statement. All proteins are formed from 20 amino acids. All proteins are soluble. Both ends of a protein are similar. Proteins are formed by glycosidic bonds.

All proteins have 20 standard amino acids. The amino acids are joined together in peptide linkage to form protein. A protein has an amino-terminal with the free amino group and the carboxy terminal with a free carboxyl group. Proteins rich in polar amino acids are soluble. So, the correct answer is option A.