Growth factors (1amino acids,(2)purines and pyrimidines,3)vitamins 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 growthGrowth 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