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Among the 20 common amino acids, five have a side chain which can be charged. At pH=7, two are negative charged: aspartic acid (Asp, D) and glutamic acid (Glu, E) (acidic side chains), and three are positive charged: lysine (Lys, K), arginine (Arg, R) and histidine (His, H) (basic side chains).Negatively charged amino acids have acidic R-groups and include aspartic acid and glutamic acid. Both of these amino acids are nonessential, meaning that they can be synthesized by the body and do not need to be obtained from the diet.