22蛋白质的基本结构单位—氨基酸 2.2.1氨基酸的基本结构和构型 存在于自然界的氨基酸有300种。动物机体的蛋白质经强酸水解之后 可以得到20种氨基酸,并且均为L氨基酸(除了甘氨酸),含不对 称的a-碳原子。它们之间的差别在于有不同的则链基团R 镜面 镜面 H H O、H R COOH H-C-OH NH, CH,OH CH,OH CH,OH CH,OH 氨基酸的结构通式 L-丝氨酸 D丝氨酸 L-甘油醛 D甘油醛 氨基酸与甘油醛的构型
2.2 蛋白质的基本结构单位——氨基酸 2.2.1 氨基酸的基本结构和构型 存在于自然界的氨基酸有300种。动物机体的蛋白质经强酸水解之后 可以得到20种氨基酸，并且均为L-氨基酸（除了甘氨酸），含不对 称的α-碳原子。它们之间的差别在于有不同的侧链基团 R。 NH2 C α R COOH H 氨基酸的结构通式 C C O O CH2OH H3N H C C O H CH2OH HO H C C O O CH2OH H NH3 C C O H CH2OH H OH 镜面 L-丝氨酸 D-丝氨酸 L-甘油醛 D-甘油醛 镜面 氨基酸与甘油醛的构型
22.2组成蛋白质的20种氨基酸 5-1 Properties and Conventions Associated with the Standard Amino Acids Abbreviated Amino acid (R group) Hydropathy in proteins (%) R groups Glycine 2.34 5.97 0.4 7.2 Alanin 2.34 5.97 Leuc ine 131 2.36 9.60 5.98 3.8 9.1 Isoleucine 131 968 6.02 4.5 5.3 Methionine 149 2.28 921 5.74 1.9 2,3 Aromatic R groups 165 1.83 9,13 548 3,9 181 2.20 9.11 10.07 5.66 Tryptophan 2.38 9.39 5.89 1.4 Polar, uncharged R groups Serine 2.21 -0.8 Proline 115 1.99 10.96 648 Threonine PTcAG 119 2.11 9.62 587 0.7 5.9 121 8.18 132 2.02 5.41 2.17 9,13 5.65 4,2 Positively charged R groups 146 8.95 10.53 9.74 39 Histidine 155 9.17 6.00 Arginine 174 2.17 904 12.48 10 Negatively charged Aspartate 133 9.60 3.65 3.5 5.3 Glutamate 147 2.19 9.67 4.25 3.22 3.5 6.3 'A scale combining hydrophobicity and hydrophilicity of R groups; it can be used to me tendency of an amino acid to seek ues) or a nyaropno te,J& bio.157.105-132 'Average occurrence in over 1150 proteins From Doolittle, R F(1989)Redundancies in protein Structure and the Principles of Profein Conformation(Fasman, G D, ed) Plenum Press, NY, pp. 599-623 n sequences In Prediction of protein
2.2.2 组成蛋白质的20种氨基酸
22.3氨基酸的分类 在中性pH条件下 按其R侧链极性和所带电荷的不同,分为四大类, 不带电荷极性氨基酸:Gly,Ser,Thr,Cys, Thr Asn,Gln 带负电荷极性氨基酸:Asp,Glu 带正电荷极性氨基酸:His,Arg,Iys 非极性氨基酸:Aa,Va,Leu,Ie,Pro,Phe,Trp,Met
2.2.3 氨基酸的分类 在中性pH条件下 按其R侧链极性和所带电荷的不同，分为四大类, 不带电荷极性氨基酸：Gly, Ser, Thr, Cys,Thr,Asn,Gln 带负电荷极性氨基酸： Asp, Glu 带正电荷极性氨基酸： His, Arg, Lys 非极性氨基酸：Ala, Val, Leu, Ile, Pro, Phe, Trp, Met
含非极性侧链基团 含极性侧链基团 Nonpolar, aliphatic R groups Polar, uncharged R groups COO COO coo COO COO COO H3N--C-H H3N-C-H H3 N-C-H HgN-C--H HgN-C-H HSN-C--H CH CH CHoOR H-C-OB CH2 CH. ch SH Glycine Alanine Valin Serine Threonine Cysteine COO COO COO COO COO COO H3N-C--H H3N-C-H H3N-C-H H H8N-C-H HSN-C-H CH H-C-CHs HoN CHe CH H2C CH CH CHs CH3 CH H2N CHs HoN leucine Methionine Isoleucine Proline Asparagine Glutamine Gly,G Ala, A Val, V Ser, S Thr, T Cys, C Leu.l Met. m eI Pro, P Asn,N GIn, Q
含非极性侧链基团 含极性侧链基团 Ser, S Thr, T Cys, C Pro, P Asn, N Gln, Q Gly, G Ala, A Val, V Leu, L Met, M Ile, I
含芳香基团 含碱性侧链基团(带正电荷) Aromatic R groups Positively charged R C00 CO0 cO0 cO0 HgN-C-H H3N-C-H H3N-C-H H3N-C-H H3N-C-H H3N-C-H CH2 CH C CH CH CH NH NHs C=NH2 nH2 Phe nenvlalanine tryptophan Lysine Histidine Phe, F; Tyr, Y; Trp, W LVs. K: Arg. R: his H
含芳香基团 含碱性侧链基团（带正电荷） Phe, F; Tyr, Y; Trp, W Lys, K; Arg, R; His, H