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Chapter 5: Q5-3P (page 127)

Which peptide has greater absorbance at 280 nm?

A. Gln–Leu–Glu–Phe–Thr–Leu–Asp–Gly–Tyr

B. Ser–Val–Trp–Asp–Phe–Gly–Tyr–Trp–Ala

Short Answer

Expert verified

Peptide B has greater absorbance because it has tryptophan and other aromatic residues.

Step by step solution

01

Tryptophan has greatest absorbance

Tryptophan has the greatest absorbance at 280nm because of its higher resonance energy transfer. Also, the fluorescence spectrum of aromatic residues such as tyrosine and phenylalanine resembles that of tryptophan.

02

Peptide B had greater absorbance

Peptide A has Gln–Leu–Glu–Phe–Thr–Leu–Asp–Gly–Tyr sequence. In this amino acid sequence, there is absence of tryptophan amino acids which has the highest absorbance. However, peptide B has Ser–Val–Trp–Asp–Phe–Gly–Tyr–Trp–Ala sequence. In this amino acid sequence, there is presence of tryptophan amino acids which has the highest absorbance due to its greater absorptivity.

Hence, peptide B has greater absorbance.

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Most popular questions from this chapter

Describe the basis for separating proteins by ion exchange, hydrophobic interaction, gel filtration, and affinity chromatography.

Explain how the number of amino acid differences between homologous proteins can be used to construct a phylogenetic tree.

You wish to sequence the light chain of a protease inhibitor from the Brassica nigra plant. Cleavage of the light chain by trypsin and chymotrypsin yields the following fragments. What is the sequence of the light chain?

Chymotrypsin

1. Leu–His–Lys–Gln–Ala–Asn–Gln–Ser–Gly–Gly–Gly–Pro–Ser

2. Gln–Gln–Ala–Gln–His–Leu–Arg–Ala–Cys–Gln–Gln–Trp

3. Arg–Ile–Pro–Lys–Cys–Arg–Lys–Phe

Trypsin

4. Arg

5. Ala–Cys–Gln–Gln–Trp–Leu–His–Lys

6. Cys–Arg

7. Gln–Ala–Asn–Gln–Ser–Gly–Gly–Gly–Pro–Ser

8. Phe–Gln–Gln–Ala–Gln–His–Leu–Arg

9. Ile–Pro–Lys

10. Lys

Consult Table 5-1 to complete the following: (a) On a plot of absorbance at 280 nm versus elution volume, sketch the results of gel filtration of a mixture containing human cytochrome c and bacteriophage T7 RNA polymerase and identify each peak. (b) Sketch the results of SDS-PAGE of the same protein mixture showing the direction of migration and identifying each band.

(a) The ESI-MS spectrum below was obtained for hen egg-white lysozyme (HEWL). Using peaks 5 and 6, calculate the molecular mass of HEWL (see Sample Calculation 5-1).

[http://www.astbury.leeds.ac.uk/facil/MStut/mstutorial.htm. Published by A.E. Ashcroft, Astbury Centre for Structural Molecular Biology, University of Leeds (2000)]

(b) What is the charge on the ion that makes peak 5?
See all solutions

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