Final answer:
Arginine is more basic than lysine because it has an additional amino group that allows for effective delocalization of positive charge, enhancing its basicity.
Step-by-step explanation:
Arginine is more basic than lysine because arginine has an additional amino group in its side chain. This guanidinium group in arginine can delocalize a positive charge more effectively compared to the ε-amino group of lysine. The side chains of both arginine and lysine are positively charged, making them basic amino acids, but the guanidinium group in arginine is more capable of sharing its positive charge over multiple nitrogen atoms, enhancing its base strength and ability to form ionic interactions.
The difference in basicity is not related to the molecular weight, the presence of hydrogen ions in lysine, or acidity properties of lysine. Instead, it is the chemical structure of the side chain that is responsible. The chemical nature of the side chain directly affects the amino acid's properties, including its basicity.