英文课件氨基酸和肽

1、5-15（1）5-25（1）5-35（1）a compound that contains both an amino group and a carboxyl group an amino acid in which the amino group is on the carbon adjacent to the carboxyl group although -amino acids are commonly written in the unionized form, they are more properly written in the(internal salt) formR R

2、- -C C H H - -C C O O H HN N H H2 2R R- -C C H H - -C C O O- -N N H H3 3+ +unionizedunionizedformformzwitterionzwitterionO OO O5-45（1）蛋白质氨基酸的构型是什么样的？蛋白质氨基酸的构型是什么样的？5-55（1）With the exception of glycine, all protein-derived amino acids have at least one stereocenter (the -carbon) and are chiral the va

3、st majority of -amino acids have the L-configuration at the -carbonH HN N H H3 3+ +C C O O O O- -C C H H3 3+ +H H3 3N NH HC C O O O O- -C C H H3 3D-AlanineD-AlanineL-AlanineL-Alanine(Fischer projections)(Fischer projections)5-65（1）Comparison of the stereochemistry of alanine and glyceraldehyde (Fisc

4、her projection formulas)H HN N H H3 3+ +C C O O O O- -C C H H3 3+ +H H3 3N NH HC C O O O O- -C C H H3 3D-AlanineD-AlanineL-AlanineL-AlanineH HO O H HC C H H O OC C H H2 2O O H HH H O OH HC C H H O OC C H H2 2O O H HD-GlyceraldehydeD-GlyceraldehydeL-GlyceraldehydeL-Glyceraldehydethe naturally the nat

5、urally occurring formoccurring formthe naturally the naturally occurring formoccurring form5-75（1）1.蛋白质氨基酸有哪些非极性侧链基团？（蛋白质氨基酸有哪些非极性侧链基团？（5-8）2.蛋白质氨基酸有哪些极性侧链基团？（蛋白质氨基酸有哪些极性侧链基团？（5-9）3.蛋白质氨基酸有哪些酸性侧链基团？（蛋白质氨基酸有哪些酸性侧链基团？（5-10）4.蛋白质氨基酸有哪些碱性侧链基团？（蛋白质氨基酸有哪些碱性侧链基团？（5-11）1. 1. 在哪些蛋白质中发现以下修饰氨基酸？在哪些蛋白质中发现以下修饰氨基

6、酸？ - -羧基谷氨酸羧基谷氨酸 、5-5-羟赖氨酸、羟赖氨酸、4-4-羟哺氨酸、羟哺氨酸、O-O-磷酸丝氨酸、甲状腺素？（磷酸丝氨酸、甲状腺素？（5-135-13）5-85（1）Nonpolar side chains (predominant form at pH 7.0)Nonpolar side chains (predominant form at pH 7.0)H H - -C C H H3 3- -C C H H3 3C C H H2 2C C H H ( (C C H H3 3) )- -( (C C H H3 3) )2 2C C H H C CH H2 2- -C C H

7、H3 3S SC C H H2 2C C H H2 2- -N NH H( (C C H H3 3) )2 2C C H Hglycine (gly, G)glycine (gly, G)alanine (ala, A)alanine (ala, A)valine (val, V)valine (val, V)leucine (leu, L)leucine (leu, L)isoleucine (ile, I)isoleucine (ile, I)methionine (met, M)methionine (met, M)phenylalanine (phe, F)phenylalanine

8、(phe, F)tryptophan (trp, W)tryptophan (trp, W)N NH HH H+ +p proline (Pro, P)roline (Pro, P)5-95（1）Polar side chains (predominant form at pH 7.0)Polar side chains (predominant form at pH 7.0)asparagine (asn, N)asparagine (asn, N)glutamine (glu, G)glutamine (glu, G)serine (ser, S)serine (ser, S)threon

9、ine (thr, T)threonine (thr, T)H H2 2N N C CC C H H2 2- -O OH H2 2N N C CC C H H2 2C C H H2 2- -O OH H O O C C H H2 2- -C C H H3 3C C H H - -O O H H5-105（1）Acidic side chains (predominant form at pH 7.0)Acidic side chains (predominant form at pH 7.0)aspartic acid (asp, D)aspartic acid (asp, D) glutam

10、ic acid (glu, E)glutamic acid (glu, E)cysteine (cys, C)cysteine (cys, C)tyrosine (tyr, Y)tyrosine (tyr, Y)- -O O C C C C H H2 2- -H H S S C CH H2 2- - -O O C C C C H H2 2C C H H2 2- -H H O OC C H H2 2- -O OO O5-115（1）B Ba as si ic c s si id de e c ch ha ai in ns s ( (p pr re ed do om mi in na an nt

11、t f fo or rm m a at t p pH H 7 7. .0 0) )a ar rg gi in ni in ne e ( (a ar rg g, , R R) )h hi is st ti id di in ne e ( (h hi is s, , H H) )l ly ys si in ne e ( (l ly ys s, , K K) )H H2 2N N C CN N H H C C H H2 2C C H H2 2C C H H2 2- -N N H H2 2+ +H H3 3N N C CH H2 2C CH H2 2C C H H2 2C C H H2 2- -N N

12、N NH HC C H H2 2- -+ +5-125（1）Note these structural features1. All 20 are -amino acids2. For 19 of the 20, the -amino group is primary; for proline, it is secondary3. With the exception of glycine, the -carbon of each is a stereocenter4. Isoleucine and threonine contain a second stereocenter5. The s

13、ulfhydryl group (pKa 8.3) of cysteine, the imidazole group (pKa 6.0) of histidine, and the phenolic hydroxyl (pKa 10.1) of phenylalanine are partially ionized at pH 7.0, but the ionic form is not the major form at this pH5-135（1）Each example is derived from a common amino acid by the modification sh

14、own in color hydroxylysine and hydroxyproline are found only in a few connective tissues such as collagen thyroxine is found only in the thyroid gland+ +H H3 3N NN N H H3 3+ +C C O O O O- -O O H HHydroxylysineHydroxylysineN NC C O O O O- -H H O OH HH HHydroxyprolineHydroxyprolineN N H H3 3+ +C C O O

15、 O O- -O OI II II IH H O OI IThyroxineThyroxine+ +5-145（1）+ +H H3 3N NC C O O O O H HpKpKa a = 2.34 = 2.34+ +H H3 3N NC C O O O O- -H H2 2N NC C O O O O- -pKpKa a = 9.69 = 9.69+1 charge+1 charge0 charge0 charge-1 charge-1 chargeIsoelectric zwitterionIsoelectric zwitterion+ +H H3 3N NC C O O O O H H+

16、2 charge+2 chargeN NN N H HH HpKpKa a = 1.82 = 1.82+ +H H3 3N NC C O O O O- -+1 charge+1 chargeN NN N H HH HpKpKa a = 6.04 = 6.04+ +H H3 3N NC C O O O O- -0 0 charge chargeN NN N H HpKpKa a = 9.17 = 9.17H H2 2N NC C O O O O- -1 charge-1 chargeN NN N H HIsoelectric zwitterionIsoelectric zwitterion+ +

17、 +5-155（1）Figure (a) Titration of alanine with NaOH 5-165（1）Figure (b) Titration of histidine with NaOH 5-175（1）1.某一氨基酸的解离过程某一氨基酸的解离过程1.甘氨酸的羧基和乙酸的羧基哪一种更酸？甘氨酸的羧基和乙酸的羧基哪一种更酸？2.如果甘氨酸的羧基更酸，解释为什么？如果甘氨酸的羧基更酸，解释为什么？3.丙氨酸的氨基和丙胺的氨基哪一个更碱？丙氨酸的氨基和丙胺的氨基哪一个更碱？4.精氨酸的胍基与赖氨酸的精氨酸的胍基与赖氨酸的 -氨基哪一种更碱？氨基哪一种更碱？5.如果精氨酸的胍基更碱

18、，解释为什么？如果精氨酸的胍基更碱，解释为什么？6.胍基和胍基和 -氨基哪一种更适合作为质子受体？氨基哪一种更适合作为质子受体？7.三种碱性侧链中哪一种既可作为质子供体又可作为质子受体三种碱性侧链中哪一种既可作为质子供体又可作为质子受体？5-185（1）The average pKa of an -carboxyl group is 2.19, which makes them considerably stronger acids than acetic acid (pKa 4.76) the greater acidity of the amino acid carboxyl group

19、is due to the electron-withdrawing inductive effect of the -NH3+ groupT Th he e a am mm mo on ni iu um m i io on n h ha as s a an ne el le ec ct tr ro on n- -w wi it th hd dr ra aw wi in ng g i in nd du uc ct ti iv ve e e ef ff fe ec ct t+ +p pK Ka a = = 2 2. .1 19 9N N H H3 3+ +N N H H3 3+ +R RC C

20、H H C C O O O O- -R RC C H H C C O O O O H HH H3 3O O+ +H H2 2O O+ +5-195（1）The average value of pKa for an -NH3+ group is 9.47, compared with a value of 10.76 for a 2 alkylammonium ion+ +pKpKa a = 9.47 = 9.47N N H H3 3+ +N N H H2 2R RC C H H C C O O O O- -R RC C H H C C O O O O- -+ + H H2 2O OH H3

21、3O O+ +pKpKa a = 10.76 = 10.76N N H H3 3+ +N N H H2 2C C H H3 3C C H H C C H H3 3C C H H3 3C C H H C C H H3 3+ + H H3 3O O+ + + H H2 2O O5-205（1）The side chain of arginine is a considerably stronger base than an aliphatic amine basicity of the guanido group is attributed to the large resonance stabi

22、lization of the protonated form relative to the neutral form+ +pKpKa a = 12.48= 12.48C CN N H H2 2+ +C CR RN N H HN N H H2 2+ +N N H H2 2N N H H2 2R RN N H HC CR RN N H HN N H H2 2N N H H2 2C CR RN NN N H H2 2N N H H2 2+ +H H3 3O O+ +H H2 2O O:5-215（1）The imidazole group on the side chain of histidi

23、ne is a heterocyclic aromatic amine+ +this lone pair is this lone pair is not a part of thenot a part of thearomatic sextet; it isaromatic sextet; it isthe proton acceptorthe proton acceptorpKpKa a 6.04 6.04N NH HN N H H3 3+ +N NH HC C H H2 2C C H H C C O O O O- -N N H H3 3+ +N NH HC C H H2 2C C H H

24、 C C O O O O- -N N+ + H H3 3O O+ +H H2 2O ON NN NH HH H+ +C C H H2 2C C H H C C O O O O- -N N H H3 3+ +: : : : :5-225（1）1.如何根据如何根据pKa和和pH计算共轭碱计算共轭碱/共轭酸（质子受体共轭酸（质子受体/质子供体质子供体）比例？）比例？2.如何根据如何根据pKa和和pH计算离子总电荷（净电荷）？计算离子总电荷（净电荷）？3.如何计算等电点？如何计算等电点？4.如何根据等电点判断蛋白质酸碱性如何根据等电点判断蛋白质酸碱性5-235（1）Given the value of

25、 pKa of each functional group, we can calculate the ratio of each acid to its conjugate base as a function of pHConsider the ionization of an -COOH writing the acid ionization constant and rearranging terms gives -COO-COO HH -COO-COO- - K Ka a = = H H3 3O O+ + = =K Ka a -COO-COO HH -COO-COO- - H H3

26、3O O+ + ororp pK Ka a = = 2 2. .0 00 0 C C O O O O- - C C O O O O H H+ +H H3 3O O+ + +H H2 2O O5-245（1） substituting the value of Ka (1 x 10-2) for the hydrogen ion concentration at pH 7.0 (1.0 x 10-7) gives at pH 7.0, the -carboxyl group is virtually 100% in the ionized or conjugate base form, and

27、has a net charge of -1 we can repeat this calculation at any pH and determine the ratio of -COO- to -COOH and the net charge on the -carboxyl at that pH= =K Ka a -COO-COO HH -COO-COO- - H H3 3O O+ + = 1.00 x 10= 1.00 x 105 51.00 x 101.00 x 10-7-71.00 x 101.00 x 10-2-2= =5-255（1）We can also calculate

28、 the ratio of acid to conjugate base for an -NH3+ group; for this calculation, assume a value 10.0 for pKa writing the acid ionization constant and rearranging gives - -N NH H2 2 - -N NH H3 3+ + K Ka a= = H H3 3O O+ + + +p pK Ka a = = 1 10 0. .0 00 0 N N H H2 2 N N H H3 3+ +H H3 3O O+ + +H H2 2O O5-

29、265（1） substituting values for Ka of an -NH3+ group and the hydrogen ion concentration at pH 7.0 gives at pH 7.0, the ratio of -NH2 to -NH3 + is approximately 1 to 1000 at this pH, an -amino group is 99.9% in the acid or protonated form and has a charge of +1 - -N NH H2 2 - -N NH H3 3+ + K Ka a= = H

30、 H3 3O O+ + = =1 1. .0 00 0 x x 1 10 0- -1 10 01 1. .0 00 0 x x 1 10 0- -7 7= = 1 1. .0 00 0 x x 1 10 0- -3 35-275（1）We have calculated the ratio of acid to conjugate base for an -carboxyl group and an -amino group at pH 7.0We can do this for any weak acid and its conjugate base at any pH using the

31、Henderson-Hasselbalch equation w we ea ak k a ac ci id d c co on nj ju ug ga at te e b ba as se e l lo og g= =p pH Hp pK Ka a + +5-285（1） using the Henderson-Hasselbalch equation, we can calculate the percent of charged or uncharged form present and the net charge on serine at pH 3.0, 7.0, and 10.0+

32、 + +pH 3.0pH 3.0pH 7.0pH 7.0pH 10.0pH 10.0Net charge +1Net charge +1N N et charge 0et charge 0N N et charge -1et charge -1100%100%86%86%99%99%100%100%88%88%100%100%C C H H2 2O O H HC C H H2 2O O H HC C H H2 2O O H HH H3 3N N - -C CH H - -C C - -O O H HH H3 3N N - -C CH H - -C C - -O O- -H H2 2N N -

33、-C CH H - -C C - -O O- -O OO OO O5-295（1） the pH at which the majority of molecules of a compound in solution have no net charge the pI for glycine, for example, falls midway between the pKa values for the carboxyl and amino groups given in the following tables are isoelectric pH values for the 20 p

34、rotein-derived amino acidsp pI I = = 1 12 2( (p p K Ka a C CO O O O H H + + p p K Ka a N N H H3 3+ +) )= = 2 21 1( (2 2. .3 35 5 + + 9 9. .7 78 8) ) = = 6 6. .0 06 65-305（1） N N H H3 3+ + C C O O O O H H6.026.025.415.415.655.655.975.976.026.026.026.025.745.745.485.486.306.305.685.686.536.535.895.895

35、.975.97pKpKa a of ofpKpKa a of ofpKpKa a of ofpIpI-valinevaline2.322.329.629.62tryptophantryptophan2.382.389.399.3910.4310.432.632.63threoninethreonineserineserine2.212.219.159.1510.6010.601.991.99prolineprolinephenylalaninephenylalanine1.831.839.139.139.219.212.282.28methioninemethionine9.689.682.3

36、62.36leucineleucineisoleucineisoleucine2.362.369.689.68glycineglycine2.342.349.609.609.139.132.172.17glutamineglutamine8.808.802.022.02asparagineasparagine9.699.692.342.34alaninealanineSide ChainSide ChainNonpolar &Nonpolar &polar side chainspolar side chainsTable 3.2 pKTable 3.2 pKa a and p

37、I of and pI of -amino acids-amino acids5-315（1） N N H H3 3+ + C C O O O O H H N N H H3 3+ + C C O O O O H H10.7610.762.982.985.025.023.083.087.647.649.749.745.635.63pKpKa a of ofpKpKa a of ofpKpKa a of ofpIpI10.0710.079.119.112.202.20tyrosinetyrosinelysinelysine2.182.188.958.9510.5310.536.106.109.18

38、9.181.771.77histidinehistidineglutamic acidglutamic acid 2.102.109.479.474.074.078.008.0010.2510.252.052.05cysteinecysteineaspartic acidaspartic acid 2.102.109.829.823.863.86argininearginine2.012.019.049.0412.4812.48Side ChainSide ChainAcidicAcidicS Side Chainside ChainspKpKa a of ofpKpKa a of ofpKp

39、Ka a of ofSide ChainSide ChainBasicBasicSide ChainsSide ChainspIpITable 3.2 (contd)Table 3.2 (contd)5-325（1）1。1）写出谷氨酸在写出谷氨酸在pH由强酸性变成强碱性过程中的解离过程，由强酸性变成强碱性过程中的解离过程，2）在等电点时分子以何种形式存在？）在等电点时分子以何种形式存在？3）计算其等电点）计算其等电点4）作滴定曲线）作滴定曲线5）pH为为1、3、5、7、9、12时氨基酸向电场中什么方向移动？时氨基酸向电场中什么方向移动？2。计算。计算4肽肽Lys-Ser-Asp-Ala的的pI

40、答案：pI=6.4（作业题）作业题）5-335（1）1.根据氨基酸的电荷特性分离氨基酸的方法有那些？根据氨基酸的电荷特性分离氨基酸的方法有那些？2.为什么纤维素、淀粉、琼脂等都能作为氨基酸电泳的支持物为什么纤维素、淀粉、琼脂等都能作为氨基酸电泳的支持物？5-345（1） the process of separating compounds on the basis of their electric charge electrophoresis of amino acids can be carried out using paper, starch, agar, certain plast

41、ics, and cellulose acetate as solid supports in paper electrophoresis, a paper strip saturated with an aqueous buffer of predetermined pH serves as a bridge between two electrode vessels5-355（1） a sample of amino acids is applied as a spot (the origin) on the solid support strip an electric potentia

42、l is applied to the electrode vessels and amino acids migrate toward the electrode with charge opposite their own molecules with a high charge density move faster than those with a low charge density molecules at their isoelectric point remain at the origin after separation is complete, the strip is

43、 dried and developed to make the separated amino acids visible5-365（1）1.肽键具有什么形式？（肽键具有什么形式？（5-37）2.肽键具有什么样的几何形状？（肽键具有什么样的几何形状？（5-40）3.写出一个三肽的结构式：写出一个三肽的结构式：Ser-Met-Asn（5-41）4.定义肽、二肽、多肽、蛋白质定义肽、二肽、多肽、蛋白质5.肽类有那些生物学功能？举例说明。（肽类有那些生物学功能？举例说明。（5-42）5-375（1）In 1902, Emil Fischer proposed that proteins are l

44、ong chains of amino acids joined by amide bonds to which he gave the name peptide bonds the special name given to the amide bond between the -carboxyl group of one amino acid and the -amino group of another5-385（1）+ +A Al la an ni in ne e ( (A Al la a) )S Se er ri in ne e ( (S Se er r) )H H3 3N NO O

45、- -H HH H O O H H2 2C CO OH H3 3N NO O- -H HC C H H3 3O OH H3 3N NN NH HH H O O H H2 2C CO OH HC C H H3 3O OO O- -H H+ + + +p pe ep pt ti id de e b bo on nd dS Se er ry yl la al la an ni in ne e ( (S Se er r- -A Al la a) )5-395（1）: the name given to a short polymer of amino acids joined by peptide b

46、onds; they are classified by the number of amino acids in the chain: a molecule containing two amino acids joined by a peptide bond: a molecule containing three amino acids joined by peptide bonds: a macromolecule containing many amino acids joined by peptide bonds: a biological macromolecule of mol

47、ecular weight 5000 g/mol or greater, consisting of one or more polypeptide chains5-405（1） the four atoms of a peptide bond and the two alpha carbons joined to it lie in a plane with bond angles of 120 about C and N to account for this geometry, Linus Pauling proposed that a peptide bond is most accu

48、rately represented as a hybrid of two contributing structures the hybrid has considerable C-N double bond character and rotation about the peptide bond is restricted(2)(2)C C C C N NH HC CC C C C O OO OC CN NH H+ +- -(1)(1): :5-415（1）By convention, peptides are written from the left, beginning with the free -NH3+ group and ending with the free -COO- group the repeat pattern, starting from the N-terminal amino acid, is N - -carbon - carbonyl carbon etc.+ +H H3 3N NO O H HN NH HO OH