phenylalanine alanine

Transcription

1 END F UNIT TET ENGINEERING PRTEIN TET 60 mrks (1 hour) A copy of the EP Informtion heet is required for this test, together with the spectroscopic dt (n.m.r.) from Tble 23 in the Dt heets. 1 nylketonuri (PKU) is potentilly lethl inherited disese. Bbies suffering from PKU lck the bility to brek down the surplus phenyllnine tht is present in their diet. Excess phenyllnine is toxic nd cuses mentl retrdtion. nyllnine is 2-mino cid (-mino cid), nd its structurl formul is given below. phenyllnine 2 N Wht feture of the structure of phenyllnine indictes tht it could be one of the building blocks of our proteins? (1 mrk) b i Drw the structurl formul of the zwitterion present in n queous solution of phenyllnine. ii A smll quntity of cid is dded to n queous solution of phenyllnine. Drw the structurl formul of the ion tht is formed, nd explin why the p of the solution does not chnge very much on ddition of the cid. (3 mrks) c nyllnine hs two stereoisomers. i Wht type of stereoisomerism is shown by phenyllnine? (1 mrk) ii Drw three-dimensionl representtions of the two isomers, showing clerly how they re relted. d Another mino cid, lnine, hs the following structurl formul. 2 N lnine i Drw structurl formule for the two different peptides tht cn be formed when phenyllnine nd lnine join to ech other. ii n one of your formule, drw circle round the peptide link. (1 mrk) iii Wht regent nd conditions re usully used in the lbortory to brek down the peptide link? (3 mrks) [TTAL: 15 MARK] 196 lters Advnced hemistry 2000 see opyright restrictions

2 END F UNIT TET EP 2 x insulin consists of two peptide chins with 21 nd 30 mino cids respectively. The digrm below shows the primry structure of ox insulin. The disulphide bridges which re importnt in determining the tertiry structure of the protein re lso displyed. The secondry structure of the insulin is determined by hydrogen bonding between the crbonyl nd mino groups. ys er Gln Ile Gln ys Al er ys ys Gln is ys er is Al ys Arg Thr Al Lys Pro Wht is ment by the following terms used in the bove pssge? i the primry structure of ox insulin ; (1 mrk) ii the secondry structure of the insulin. b Drw digrm to represent the hydrogen bonding between the crbonyl groups, =, nd the mino groups, N, in the peptide chins. n your digrm show the polrity of the different toms. (3 mrks) c Enzymes, like ll proteins, hve precise tertiry structure. i Explin why the tertiry structure of protein is importnt in determining how the enzyme works. ii Enzymes lose their ctivity when heted. Explin this in terms of their shpe nd the intermoleculr forces present. iii The ction of some enzymes is sensitive to p. Explin how enzymes might be dectivted by smll chnges of p tht do not ffect the tertiry structure. [TTAL: 12 MARK] lters Advnced hemistry 2000 see opyright restrictions 197

3 END F UNIT TET 3 Forestry workers suffer bdly from the bites of insects such s midges. The liquid DIMP ws developed s n effective insect repellent. This is n ester clled dimethylphthlte. An experiment ws set up to determine how quickly DIMP hydrolysed in cidic conditions t room temperture, ccording to the eqution below. The concentrtion of DIMP in n cidic solution ws determined t mesured time intervls. The initil concentrtions of the rectnts were mol dm 3 of DIMP nd mol dm 3 of + (q) DIMP i uggest method by which the progress of the rection could be followed (i.e. the concentrtion of DIMP mesured t time intervls s the rection proceeds). ii Use the grph below to determine the first three hlf-lives of DIMP. (3 mrks) [DIMP] / mol dm Time / s iii Wht is the order of rection with respect to DIMP? Give reson for your nswer. b Further experiments showed tht the order of the rection with respect to + (q) concentrtion ws first order. Use this informtion nd your nswer to prt iii to write the rte eqution for the rection. [TTAL: 9 MARK] Norml hemoglobin (ba) is protein mde up of four subunits, two chins nd two b chins. People who suffer from the inherited disese sickle-cell nemi mke bnorml hemoglobin (b), in which the b chins hve one mino cid in their sequence different from tht in norml hemoglobin. The condition is cused by single error in the DNA tht codes for the b chin. Messenger RNA (mrna) molecules crry the instructions for mking the protein chins from the DNA in the cell nucleus to the ribosomes, where protein synthesis tkes plce. Ech mrna molecule hs sequence of bses tht codes for the mino cid units in the chin. Moving from the N 2 end of the b chin, these re: ( N 2 end) mrna for norml hemoglobin (ba) GUGAUGAUUGAGGAGAAG mrna for sickle-cell hemoglobin (b) GUGAUGAUUGUGGAGAAG lters Advnced hemistry 2000 see opyright restrictions

4 END F UNIT TET EP i Look t the sequence of bses in the mrna for ba nd b nd find the one tht is different. ounting from the N 2 end, for which codon does this difference occur? (A codon is sequence of three bses, or triplet, tht codes for prticulr mino cid.) (1 mrk) ii Use the EP Informtion heet provided to nme the mino cid in ba which hs been replced in b. (1 mrk) b The mrna is mde in the cell nucleus from DNA. i Use the symbols bse, sugr nd phosphte to drw digrm representing double strnd of DNA. (3 mrks) ii Which intermoleculr forces hold the two chins of DNA together? Indicte their position on your digrm by dotted lines. c i Briefly explin how genetic engineering might be used to ttempt to cure sickle-cell nemi. ii Mny people believe tht the widespred use of genetic engineering is not justified. Give one dvntge nd one disdvntge of the technique. [TTAL: 11 MARK] 5 Ethnol is widely used in the chemicl industry s solvent for orgnic compounds. It is mnufctured by recting ethene with stem over phosphoric cid ctlyst. 2 4 (g) + 2 (g) D 2 5 (g) D= 46 kj mol 1 i Write n expression for the equilibrium constnt, K c, for the rection, in terms of the concentrtions of rectnts nd products. ii Use the informtion below to clculte the equilibrium concentrtion of ethnol vpour under these conditions. (3 mrks) Temperture 570 K Pressure 60 tm K c 24 dm 3 mol 1 t 570 K [ 2 (g)] (t equilibrium) mol dm 3 [ 2 4 (g)] (t equilibrium) 0.45 mol dm 3 b i Will the equilibrium constnt be lrger, smller or the sme t 670 K? Explin your nswer. (3 mrks) ii Describe nd explin the effect of incresing the pressure in the rection vessel on: 1 the equilibrium constnt; (1 mrk) 2 the composition of the equilibrium mixture. (1 mrk) iii uggest why higher pressure is not used for this process. (1 mrk) c A pure smple of one of the components of the equilibrium mixture hs the low-resolution n.m.r. spectrum shown below. Use the spectrum nd Dt heet (Tble 23) to identify the compound. Explin your resoning. Absorption TM hemicl shift [TTAL: 13 MARK] (Adpted from R hemistry (lters), Pper 1, question 3, 1995) lters Advnced hemistry 2000 see opyright restrictions 199

5 END F UNIT TET EP INFRMATIN EET Amino cid Abbrevition R group cine Alnine Al 3 ine 3 3 cine Isoleucine Ile nyllnine 2 Proline Pro N Trytophn Trp 2 Amino cid Abbrevition ysteine ys Methionine Met Asprtic cid Asp tmic cid Asprgine tmine Gln osine istidine is R group N N erine Threonine er Thr N 2 3 Lysine Arginine Lys Arg N N N N N 2 N Tble 1 The twenty mino cids tht mke up proteins First bse econd bse Third bse U A G U UUU UU er UAU UGU ys U UU U er UA UG ys UUA UA er UAA top UGA top A UUG UG er UAG top UGG Trp G UU U Pro AU is GU Arg U U Pro A is G Arg UA A Pro AA Gln GA Arg A UG G Pro AG Gln GG Arg G A AUU Ile AU Thr AAU AGU er U AU Ile A Thr AA AG er AUA Ile AA Thr AAA Lys AGA Arg A AUG Met AG Thr AAG Lys AGG Arg G G GUU GU Al GAU Asp GGU U GU G Al GA Asp GG GUA GA Al GAA GGA A GUG GG Al GAG GGG G Tble 2 The triplet bse codes (codons) for ech mino cid used in messenger RNA 200 lters Advnced hemistry 2000 see opyright restrictions