E 20 standard amino acids 3. Polar, uncharged r groups(6) CoO COo COo H3N-H N—H CH,OH CHOH CH?SH CH Serine(ser) Threonine(thr Cysteine(Cys) 丝氨酸 苏氨酸 半胱氨酸 COO COO COO H 3 N H 3 CH 2 CH CH 2 CH2SCH3 CONH 2 CH 2 CONH 2 Methionine met) Asparagine(Asn) Glutamine(Gin) 甲硫氨酸(蛋氨酸) 门冬酰胺 谷氨酰胺（二）20 standard amino acids +H3N COO￾H CH2OH +H3N COO￾H CHOH +H3N COO￾H CH2SH +H3N COO￾H CH2 +H3N COO￾H CH2 CH2SCH3 CONH2 Serine (Ser) Threonine (Thr) Cysteine (Cys) Methionine (Met) Asparagine (Asn) Glutamine (Gln) 丝氨酸 苏氨酸 半胱氨酸 甲硫氨酸（蛋氨酸） 门冬酰胺 谷氨酰胺 3. Polar, uncharged R groups (6) CH3 +H3N COO￾H CH2 CH2 CONH2