)20 standard amino acids 5. Positively charged r groups 3) COo Coo H3N H HrN-H CH 2 CH COo 2 CH CH HaN H 2 2 CH 2 CH 2 HoC CH. NH imidazole NH guanidin C=NH2 NH HNS NH 2 ysine (lys Arginine (arg) Histidine 赖氨酸 精氨酸 组氨酸 Basic amino acids containing two amino groups（二）20 standard amino acids Basic amino acids —— containing two amino groups +H3N COO￾H CH2 CH2 Lysine (Lys) Arginine (Arg) 赖氨酸 精氨酸 +H3N COO￾H CH2 CH2 CH2 5. Positively charged R groups (3) CH2 CH2 NH3+ NH C NH2 NH2+ +H3N COO￾H H2C HN guanidino NH imidazole Histidine 组氨酸