Growth Factors Amino acids are needed for protein synthesis, purines and pyrimidines for nucleic acid synthesis. Vitamins are small organic molecules that usually make up all or part enzyme cofactors, and only very small amounts are required for growth. (1)amino acids, (2) purines and pyrimidines, (3) vitaminsGrowth Factors Amino acids are needed for protein synthesis, purines and pyrimidines for nucleic acid synthesis. Vitamins are small organic molecules that usually make up all or part enzyme cofactors, and only very small amounts are required for growth. (1)amino acids, (2) purines and pyrimidines, (3) vitamins