Buffers

1
BC 367 Review Questions for Exam 1
2
250 mL of 1.0 M HCl is added to 1.0 L of a 1.0 M
acetic acid/sodium acetate buffer at pH 4.76 (pKa
4.76). What is pH of the final solution?
A. 5.24 B. 4.28 C. 4.55 D. 3.86 E. 4.76 (this is
a buffer!)
3
What effect would hypoventilating (slow and
shallow breathing) have on the blood?

1. No change in blood pH.
2. A decrease in CO2, causing an increase in H
   and decrease in pH.
3. An increase in CO2, causing an increase in H
   and decrease in pH.
4. A decrease in CO2, causing an increase in H
   and increase in pH.
5. An increase in CO2, causing a decrease in H
   and increase in pH.

4
This titration curve is for what amino acid?

• http//cti.itc.virginia.edu/cmg/Demo/markPka/mark
  PkaApplet.html
• a) Arg b) His c) Leu d)
  Cys e) Glu

5

• You want to separate a mixture of three
  hypothetical proteins, all of which repeat
  certain amino acid sequences. The sequences and
  their masses are below. What should you use to
  best separate these proteins?

A. Gel filtration column B. CM-sephadex column
run at pH 7 C. Gel electrophoresis D. Affinity
chromatography E. Paper chromatography
Protein Repeating amino acid sequence Mr
Protein 1 Val-Lys-Arg 22 900
Protein 2 Gln-Phe-Gly 59 000
Protein 3 Asp-Leu-Glu 23 100
6

• Which of these peptides would be least soluble in
  a solution at a pH of 5.5?
• a) (Arg-Gly)2
• b) (Met-Asp-Val)3
• c) (Phe-Lys)5
• d) (Asn-Phe-Gln)3
• e) (Ala-Pro-Ile)3

7
A peptide was exposed to two separate enzyme
digests to yield the fragments shown below. At
physiological pH, what is the approximate net
charge of the last five residues prior to
digestion? Chymotrypsin
Trypsin Arg-Trp
Trp-Lys Asp
Met-Phe-Asp Lys-Arg-Met-Phe
Leu-Phe-Arg Lys-Leu-Phe
Lys
Arg A) -1 B) 0 C) 1 D) 2 E) Not enough
information
8
Which one of the following peptides is most
likely to adopt an alpha helix? A)
Arg-Thr-Ile-Val-Tyr-Phe-Trp-Ile B)
Arg-Ala-Trp-Glu-Gly-Arg-Arg-Asp C)
Ala-Glu-Leu-Ala-Lys-Ala-Met-Asp D)
Val-Thr-Gly-Pro-Thr-Asn-Pro-Arg E) None of these
peptide will be alpha helical because they all
contain left-handed amino acids.
9

• Protein A contains 1000 amino acids and has a
  unit evolutionary period of 6 million years.
  Protein A has an ortholog in another species that
  diverged 12 million years ago. How many amino
  acids differ between the sequences of the two
  orthologs of protein A?
• 200
• 100
• 20
• 10
• 2