Chemistry 114A (Midterm Practice Problem Set): Fall 2007
1. The pKa of the amino group in alanine is 9.62.
In a solution at pH 8.62, what
fraction of the amino groups is unprotonated?
2) A protein has a molecular weight of l60,000.
Roughly how many amino acid
residues ( average MW of an amino acid is 110) does it contain?
3) In a solution of pH 1
lysine will be more negatively charged than glutamic acid.
lysine will be more positively charged than glutamic acid.
lysine and glutamic acid will carry the same net charge.
none of the above
4. What is the isoelectric point of cysteine? (pK1 = 1.96, pK2 = 8.18 and pK3 =
5. Over what approximate pH ranges would glutamic acid exhibit significant
Only 5 to 8.5, B.
Only 3 to 5, C.
Only 8.5 to 10.5, D.
Only 1 to 3 and 8.5 to
Only 1 to 5 and 8.5 to 10.5
6. Which of the following amino acids can buffer most effectively at physiological
7. Which amino acid contains a sulfur atom?
8. How many peptides or free amino acids would result from treatment of the
following peptide with trypsin?