Year 12 AS Biology Module 1: Biological MoleculesName:
PAPER CHROMATOGRAPHY QUESTIONS
1A dipeptide was heated with an acid for 20 minutes. Three different samples were taken and loaded onto a piece of chromatography paper. These were:
1the dipeptide only;
2the dipeptide after it had been heated with the acid for 2 minutes;
3the dipeptide after it had been heated with the acid for 20 minutes.
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(a)What type of reaction results in the conversion of a dipeptide to amino acids?
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(1)
(b)Explain why three spots were obtained when the dipeptide was heated with the acid for 2 minutes.
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(c)(i)Calculate the Rf value of spot X. Show your working.
Rf = ......
(2)
(ii)Explain how you could use the Rf values to identify spot X.
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(Total 6 marks)
2(a)Describe how the process of paper chromatography is carried out in order to separate substances in a mixture.
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(3)
(b)Some fatty acids were synthesised in which all the carbon atoms were radioactive.
A mixture of three of these fatty acids was separated using paper chromatography. The level of radioactivity in each of the fatty acids was measured by passing the chromatography strip under a Geiger counter and the level was plotted as a graph. The results are shown in the diagram.
(i)The total level of radioactivity in each of the fatty acids was measured by estimating the total area under each curve rather than the height of each peak. Explain why.
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(ii)Suggest one reason why the three fatty acids showed different levels of radioactivity.
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(Total 5 marks)
3A tripeptide is made up of three amino acids. The diagram shows the molecular structure of a tripeptide.
(a)(i)Give the formula of the chemical group at position X on the molecule
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(ii)Give one piece of evidence from the diagram that this molecule is made up from three amino acids
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(b)This tripeptide was broken down into its amino acids. These were separated and identified using chromatography. The diagram shows the resulting chromatogram.
(i)Mark the diagram with a line to show where the solvent should come to when the apparatus is set up.
(1)
(ii)The tripeptide was completely broken down into its amino acids but there are only two spots on the chromatogram. Explain why.
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(iii)Give the formula which would allow you to calculate the Rf value of amino acid A from the chromatogram.
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(iv)To identify an amino acid, it is necessary to calculate Rf values rather than measure only the distance moved by the spot. Explain why
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(2)
(Total 7 marks)