October 1, 1997
Amino Acid Sequence Problem
A peptide had the following amino acid composition obtained by acid hydrolysis and amino acid
analysis: Arg, Ala, Gly, Glu, Leu, Lys, Pro, Ser, Tyr
The peptide was processed by the Dansyl-chloride method and Dansyl-Ala was found.
Next the peptide was treated with trypsin which gave 2 peptides, called T-1 and T-2.
T-1 was a
tetrapeptide with amino acid composition: Tyr, Glu, Ser, Gly.
Edman degradation yielded Gly as first
amino acid released and then Tyr.
T-2 was a pentapeptide with amino acid composition of Lys, Pro,
Ala, Arg, Leu.
Edman degradation yielded Ala first, then Leu, then Arg.
Chymotrypsin treatment of the peptide gave 2 peptides, called C-1 and C-2. C-1 had amino acid
composition (acid hydrolysis): Ala, Tyr, Gly, Arg, Lys, Pro, Leu.
Edman degradation of C-1 gave Ala
cycle, Leu in 2
cycle and Arg in 3
C-2 had amino acid composition (acid hydrolysis): Ser,
Edman degradation of C-2 gave Ser in 1st cycle and the amino acid Glu was remaining.
What is the sequence of the peptide?
Draw the full chemical structure of the peptide at pH 7.
What is the net charge on the peptide at pH 1, 5, 7, 10, 13?
What is the pI?
pK values for amino acids: Gly - 2.4, 9.8; Ala - 2.4, 9.9;
Tyr - 2.2, 9.1; Pro - 2.0, 10.7;
Glu - 2.1, 4.1, 9.5; Gln 2.2, 9.1; Arg 1.8, 9.0, 12.5; Lys 2.2, 9.2, 10.8; Ser 2.2, 9.2; Leu 2.3, 9.7
25 Points - Cell Structure and Function (5 points each short answer)
What is an enzyme and what does it do in the cell?
How many amino acids are encoded by the genetic code?
Could there be more?
Why not more?
What is the difference between DNA and RNA in chemical structure (Deoxyribo-Nucleic Acid
versus Ribo-Nucleic Acid) and in biological function?