14. Hydrocarbons
A section of Chemistry, 9701
Listing 10 of 313 questions
Amino acids such as alanine are essential building blocks for making proteins. They can be synthesised by a general reaction of which the following is an example. CH3CHO CH3CH(NH2)CO2H alanine NaCN + NH4Cl E, C3H6N2 H3O+ + heat neutralise Suggest the structure of the intermediate compound E by drawing its structural formula in the box above. Suggest, in the box below, the structural formula of the starting material needed to synthesise phenylalanine by the above general reaction. CH2 NH2 CO2H phenylalanine intermediate CH What is a protein? Using alanine as an example, draw a diagram to show how proteins are formed from amino acids. Show two repeat units in your answer. The hydrolysis of compound F produces two compounds G and H. O O G F + NH CO2H CH3 HN H State the reagents and conditions needed for this hydrolysis. Draw the structures of the two products G and H in the boxes above. Draw the zwitterionic structure of alanine. Suggest the structural formulae of the zwitterions that could be formed from the following compounds. compound zwitterion H2N CO2H NHCH3 OH NH2 HO S O O Solutions of amino acids are good buffers. What is meant by the term buffer? Write an equation to show how a solution of alanine, CH3CH(NH2)CO2H, behaves as a buffer in the presence of an acid such as HCl. Briefly describe how the pH of blood is controlled. Calculate the pH of the buffer formed when 10.0 cm3 of 0.100 mol dm–3 NaOH is added to 10.0 cm3 of 0.250 mol dm–3 CH3CO2H, whose pKa = 4.76. pH =
9701_w11_qp_43
THEORY
2011
Paper 4, Variant 3
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A mixture of amino acids can be separated by electrophoresis. During an electrophoresis experiment, ● different amino acids move in different directions, ● different amino acids move at different speeds, ● some amino acids do not move at all. Explain these observations. A mixture of amino acids can also be separated by thin-layer chromatography. Identify the mobile and the stationary phases in this type of chromatography. mobile phase stationary phase What is the process by which thin-layer chromatography can separate a mixture? State three structural features of DNA. Some diseases are caused by a mutation in the DNA base sequence which results in one amino acid being replaced by another during protein synthesis. Suggest what changes in the interactions that form the tertiary structure would result from a mutation that replaced a valine residue with a serine residue. CH3 CH3 CH C HC val NH O OH CH2 CH C ser NH O replaced by
9701_w14_qp_41
THEORY
2014
Paper 4, Variant 1
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A mixture of amino acids can be separated by electrophoresis. During an electrophoresis experiment, ● different amino acids move in different directions, ● different amino acids move at different speeds, ● some amino acids do not move at all. Explain these observations. A mixture of amino acids can also be separated by thin-layer chromatography. Identify the mobile and the stationary phases in this type of chromatography. mobile phase stationary phase What is the process by which thin-layer chromatography can separate a mixture? State three structural features of DNA. Some diseases are caused by a mutation in the DNA base sequence which results in one amino acid being replaced by another during protein synthesis. Suggest what changes in the interactions that form the tertiary structure would result from a mutation that replaced a valine residue with a serine residue. CH3 CH3 CH C HC val NH O OH CH2 CH C ser NH O replaced by
9701_w14_qp_42
THEORY
2014
Paper 4, Variant 2
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