英文課件氨基酸和肽

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）蛋白質(zhì)氨基酸的構型是什么樣的？蛋白質(zhì)氨基酸的構型是什么樣的？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.蛋白質(zhì)氨基酸有哪些非極性側(cè)鏈基團？（蛋白質(zhì)氨基酸有哪些非極性側(cè)鏈基團？（5-8）2.蛋白質(zhì)氨基酸有哪些極性側(cè)鏈基團？（蛋白質(zhì)氨基酸有哪些極性側(cè)鏈基團？（5-9）3.蛋白質(zhì)氨基酸有哪些酸性側(cè)鏈基團？（蛋白質(zhì)氨基酸有哪些酸性側(cè)鏈基團？（5-10）4.蛋白質(zhì)氨基酸有哪些堿性側(cè)鏈基團？（蛋白質(zhì)氨基酸有哪些堿性側(cè)鏈基團？（5-11）1. 1. 在哪些蛋白質(zhì)中發(fā)現(xiàn)以下修飾氨基酸？在哪些蛋白質(zhì)中發(fā)現(xiàn)以下修飾氨基

6、酸？ - -羧基谷氨酸羧基谷氨酸 、5-5-羥賴氨酸、羥賴氨酸、4-4-羥哺氨酸、羥哺氨酸、O-O-磷酸絲氨酸、甲狀腺素？（磷酸絲氨酸、甲狀腺素？（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.某一氨基酸的解離過程某一氨基酸的解離過程1.甘氨酸的羧基和乙酸的羧基哪一種更酸？甘氨酸的羧基和乙酸的羧基哪一種更酸？2.如果甘氨酸的羧基更酸，解釋為什么？如果甘氨酸的羧基更酸，解釋為什么？3.丙氨酸的氨基和丙胺的氨基哪一個更堿？丙氨酸的氨基和丙胺的氨基哪一個更堿？4.精氨酸的胍基與賴氨酸的精氨酸的胍基與賴氨酸的 -氨基哪一種更堿？氨基哪一種更堿？5.如果精氨酸的胍基更堿

18、，解釋為什么？如果精氨酸的胍基更堿，解釋為什么？6.胍基和胍基和 -氨基哪一種更適合作為質(zhì)子受體？氨基哪一種更適合作為質(zhì)子受體？7.三種堿性側(cè)鏈中哪一種既可作為質(zhì)子供體又可作為質(zhì)子受體三種堿性側(cè)鏈中哪一種既可作為質(zhì)子供體又可作為質(zhì)子受體？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.如何根據(jù)如何根據(jù)pKa和和pH計算共軛堿計算共軛堿/共軛酸（質(zhì)子受體共軛酸（質(zhì)子受體/質(zhì)子供體質(zhì)子供體）比例？）比例？2.如何根據(jù)如何根據(jù)pKa和和pH計算離子總電荷（凈電荷）？計算離子總電荷（凈電荷）？3.如何計算等電點？如何計算等電點？4.如何根據(jù)等電點判斷蛋白質(zhì)酸堿性如何根據(jù)等電點判斷蛋白質(zhì)酸堿性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）寫出谷氨酸在寫出谷氨酸在pH由強酸性變成強堿性過程中的解離過程，由強酸性變成強堿性過程中的解離過程，2）在等電點時分子以何種形式存在？）在等電點時分子以何種形式存在？3）計算其等電點）計算其等電點4）作滴定曲線）作滴定曲線5）pH為為1、3、5、7、9、12時氨基酸向電場中什么方向移動？時氨基酸向電場中什么方向移動？2。計算。計算4肽肽Lys-Ser-Asp-Ala的的pI

40、答案：pI=6.4（作業(yè)題）作業(yè)題）5-335（1）1.根據(jù)氨基酸的電荷特性分離氨基酸的方法有那些？根據(jù)氨基酸的電荷特性分離氨基酸的方法有那些？2.為什么纖維素、淀粉、瓊脂等都能作為氨基酸電泳的支持物為什么纖維素、淀粉、瓊脂等都能作為氨基酸電泳的支持物？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.肽鍵具有什么形式？（肽鍵具有什么形式？（5-37）2.肽鍵具有什么樣的幾何形狀？（肽鍵具有什么樣的幾何形狀？（5-40）3.寫出一個三肽的結構式：寫出一個三肽的結構式：Ser-Met-Asn（5-41）4.定義肽、二肽、多肽、蛋白質(zhì)定義肽、二肽、多肽、蛋白質(zhì)5.肽類有那些生物學功能？舉例說明。（肽類有那些生物學功能？舉例說明。（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