Chapter 5: Q5-1P (page 127)
It has been hypothesized that early life-forms used only eight different amino acids to build small peptides. How many different 10-residue peptides could be constructed from eight amino acids?
810 Possibilities can be constructed from eight amino acids.
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Separate cleavage reactions of a polypeptide by CNBr and chymotrypsin yield fragments with the following amino acid sequences. What is the sequence of the intact polypeptide?
CNBr treatment
1. Arg–Ala–Tyr–Gly–Asn
2. Leu–Phe–Met
3. Asp–Met
Chymotrypsin
4. Met–Arg–Ala–Tyr
5. Asp–Met–Leu–Phe
6. Gly–Asn
You wish to determine the sequence of a short peptide. Cleavage with trypsin yields three smaller peptides with the sequences Leu–Glu, Gly–Tyr– Asn–Arg, and Gln–Ala–Phe–Val–Lys. Cleavage with chymotrypsin yields three peptides with the sequences Gln–Ala–Phe, Asn–Arg–Leu–Glu, and Val–Lys–Gly–Tyr. What is the sequence of the intact peptide?
Protein X has an absorptivity of 0.4mL · mg-1· cm-1 at 280nm. What is the absorbance at 280nm of a 2.0 mg · mL-1solution of protein X? (Assume the light path is 1cm.)
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.
You wish to determine the sequence of a polypeptide that has the following amino acid composition.
1 Ala 4 Arg 2 Asn 3 Asp 4 Cys 3 Gly 1 Gln 4 Glu 1 His 1 Lys 1 Met 1 Phe 2 Pro 4 Ser 2 Tyr 1 Trp
(a) What is the maximum number of peptides you can expect if you cleave the polypeptide with cyanogen bromide?
(b) What is the maximum number of peptides you can expect if you cleave the polypeptide with chymotrypsin?
(c) Analysis of the intact polypeptide reveals that there are no free sulfhydryl groups. How many disulfide bonds are likely to be present?
(d) How many different arrangements of disulfide bonds are possible?
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