COO-α carboxyRgroupH-C-R(sidechain)Cα(α carbon)Unless side chainNHtcharged at pH 7,thisiszwitterion(doubleαaminoortwinion)ProtonationstateatpH7Every aminoacidhas at least2ionizablegroupsEveryamino acidhasbothacidand baseproperties
Every amino acid has at least 2 ionizable groups. Every amino acid has both acid and base properties
Amino acids canbe classified byR groups.five main classes:- nonpolar, aliphatic (7)hydrophobic- aromatic (3) [,aro'maetik)- polar, uncharged (5)- positively charged (3)Hydrophilic (charged)-negativelycharged(2)
Amino acids can be classified by R groups hydrophobic Hydrophilic (charged) [ˌærəˈmætɪk]
Nonpolar, aliphatic R groupsHydrocarbonchainNonpolar,aliphaticRgroupsthehydrophobicCOO-COOCOO-COO-effectstabilizesHH,N-C-HH,N-C-HH,N-C一Hprotein structureHNCH2HCH3CHH2CCH2CH3CH3GlycineProlineValineAlanineCOOCOO-COOH,N-CHaNHaN--H-HHCH-C-CH3CH2CH2CH2CH2CHCH3CH3CH3CH3["lu:si.n]IsoleucineMethionineLeucineNelson & Cox, Lehninger Princples of Biochemisty, e,2021W.H,Freeman and Company[me'Sala,ni:n]
Hydrocarbon chain [meˈθaɪəˌniːn] [ˈluːsiːn]
Aromatic R Groups·RgroupsabsorbUVAromaticRgroupsCOO-COO-COO-light at 270-280 nmH,N-CHHN-C-HH3N-CHCH2CH2CH2cancontributetotheCHhydrophobic effectNHOH[fen'lelani:]'talrasinPhenylalanineTryptophanTyrosinebenzene/'benzi:n/苯环triptafaenNelson&Cox,LehningerPrinciplesofBiochemistry.8e,2021W.H.FreemanancCompany
benzene /ˈbenziːn /苯环 [fenɪ′læləni:] ˈtaɪrəsi:n ˈtrɪptəfæn
Polar, Uncharged R GroupsPolar,uncharged Rgroups·RgroupscanformCOOCOO-cOO"hydrogen bondsH,N-C-HH,NHaN--CH一HCH2CH2H-C-OH1cysteine canformSHOHCH3disulfidebondsThreonineSerineCysteineeri.a,ni.n[seri:n]COO-COO-They canform hydrogen bondsHNHaNHFCH2CH2CH2HNH,N[as'paerad3i:n]GlutamineAsparagineNelson&Cox,LehningerPrinciplesofBiochemistry.e,2021.W.H.FreemananCompany
They can form hydrogen bonds θriːəˌniːn ['seri:n] [əs'pærədʒi:n]