1 Amino acids

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Oxford Textbook Pages : 458 - 459

CGP Revision Guide Pages : 182

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Show Specification Ref : 3.3.13.1

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Question 1 / 5

January 2012 QP – Unit 4 AQA Chemistry A-level_question_7 do not write outside the box the amino acids aspartic acid and phenylalanine react together to form a dipeptide this dipeptide can be converted into a methyl ester called aspartame h n c cooh h n ch cooh ch h o hh cooh h n cc o ch ch ch cooh aspartic acid phenylalanine aspartame aspartame has a sweet taste and is used in soft drinks and in sugar free foods for people with diabetes hydrolysis of aspartame forms methanol initially after a longer time the peptide link breaks to form the free amino acids neither of these amino acids tastes sweet a apart from the release of methanol suggest why aspartame is not used to sweeten foods that are to be cooked mark extra space b give the iupac name of aspartic acid mark c draw the organic species formed by aspartic acid at high ph mark wmp jan chem d draw the zwitterion of phenylalanine do not write outside the box mark e phenylalanine exists as a pair of stereoisomers e i state the meaning of the term stereoisomers marks e ii explain how a pair of stereoisomers can be distinguished marks extra space turn over wmp jan chem
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Question 2 / 5

June 2010 QP – Unit 4 AQA Chemistry A-level_question_6 a consider the tripeptide shown below that is formed from three amino acids k l and m do not write outside the box h n ch co nh ch ch ch nh co nh cooh from k from l from m a i name the process by which the tripeptide is split into three amino acids mark a ii give the iupac name for the amino acid k mark a iii draw the structure of the zwitterion of amino acid l a iv draw the structure of the species formed by amino acid m at low ph mark mark wmp jun chem b consider the amino acid serine do not write outside the box h n cooh ch oh b i draw the structure of the product formed when serine reacts with an excess of ch br b ii draw the structure of the dipeptide formed by two molecules of serine mark turn over for the next question mark turn over wmp jun chem
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Question 3 / 5

June 2011 QP – Unit 4 AQA Chemistry A-level_question_4 do not write outside the box the amide or peptide link is found in synthetic polyamides and also in naturally occurring proteins a i draw the repeating unit of the polyamide formed by the reaction of propanedioic acid with hexane diamine a ii in terms of the intermolecular forces between the polymer chains explain why polyamides can be made into fibres suitable for use in sewing and weaving whereas polyalkenes usually produce fibres that are too weak for this purpose marks marks extra space wmp jun chem do not write outside the box b i name and outline a mechanism for the reaction of ch ch cocl with ch nh name of mechanism mechanism b ii give the name of the product containing an amide linkage that is formed in the reaction in part b i mark c the dipeptide shown below is formed from two different amino acids marks ch cooh h n c c n c ch sh h o h h draw the structure of the alternative dipeptide that could be formed by these two amino acids question continues on the next page mark turn over wmp jun chem d the amino acids serine and aspartic acid are shown below do not write outside the box ch oh cooh h c cooh h c ch cooh nh serine nh aspartic acid d i give the iupac name of serine mark d ii draw the structure of the species formed when aspartic acid reacts with aqueous sodium hydroxide d iii draw the structure of the species formed when serine reacts with dilute hydrochloric acid mark mark d iv draw the structure of the species formed when serine reacts with an excess of bromomethane mark wmp jun chem
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Question 4 / 5

June 2013 QP – Unit 4 AQA Chemistry A-level_question_6 do not write outside the box alanine and aspartic acid are naturally occurring amino acids ch cooh h c c cooh h c cooh nh alanine nh aspartic acid a draw the structure of the zwitterion formed by alanine b draw the structure of the compound formed when alanine reacts with methanol in the presence of a small amount of concentrated sulfuric acid mark c draw the structure of the species formed by aspartic acid at high ph d draw the structure of a dipeptide formed by two aspartic acid molecules mark mark mark wmp jun chem
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Question 5 / 5

June 2016 QP – Unit 4 AQA Chemistry A-level_question_5 do not write outside the box proteins contain sequences of amino acids joined by peptide links amino acid chains polypeptides are attracted to each other by hydrogen bonding a i a section of a protein is formed from one molecule of each of the amino acids glycine h nch cooh and alanine h nch ch cooh add bonds and atoms to the diagram to complete a structural formula for this section of the protein marks a ii draw a diagram to show how an amino acid chain can form a hydrogen bond with another amino acid chain your diagram need only show the relevant atoms from one amino acid in each chain mark wmp jun chem do not write outside the box b leucine serine and glutamic acid are naturally occurring amino acids ch chch nh cooh hoch nh cooh hooc ch nh cooh leucine serine glutamic acid b i give the iupac name of leucine mark b ii draw the structure of the zwitterion of serine b iii draw the structure of the ester formed by two molecules of serine b iv draw the structure of the species formed by glutamic acid at low ph mark mark mark turn over wmp jun chem
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