1. The pH of a 0.02 M solution of an acid was measured as 4.6.
a) What is the [H+] of the solution?
b) What is the acid dissociation constant K and the pK for this acid?
2. What are the [H+] and the pH of 500 ml of 2.5 X 10-9M NaOH?
3. How many grams of sodium succinate (FW = 10 g/mol) and disodium succinate (FW = 162 g/mol) must be added to 1 L of water to produce a solution with a solution with pH 6.0 and a total succinate solute concentration of 50 mM? (for succinic acid pK1 = 4.21, pK2 = 5.64)
4. A diploid organism with a 45,000-kb haploid genome contains 21% G residues. Calculate the number of A, C, G, and T residues in the DNA of each cell in this organism.
5. Determine the subunit composition of a protein from the following information:
Molecular mass by gel filtration: 400 kD
Molecular mass by SDS-PAGE: 100 kD
Molecular mass by SDS-PAGE with 2-mercaptoethanol: 40 kD and 60 kD
6. The crocodile, which can remain under water without breathing for up to 1 hr, drowns its air-breathing prey and then dines at its leisure. An adaptation that aids the crocodile in doing so is that it can utilize virtually 100% of the O2 in its blood whereas humans, for example, can extract only about 65% of the oxygen in their blood. Crocodile Hb does not bind BPG. However, crocodile deoxyHb preferentially binds HCO3-. How does this help the crocodile obtain his dinner?
7. A peptide has the sequence
What is the charge on the peptide at pH 3, 8 and 11?
8. The highly pathogenic anaerobic bacterium Clostridium perfringens is responsible for gas gangrene, a condition where animal tissue is destroyed. This bacterium secretes an enzyme that efficiently catalyzes the hydrolysis of a specific peptide bond as show below:
-X-Gly-Pro-Y- + H2O → -X-COO- + +H3N-Gly-Pro-Y-
where X and Y are any of the 20 common amino acids.
How does the secretion of this enzyme contribute to the invasiveness of this bacterium? Why does this enzyme not affect the bacterium itself?
9. When a higher vertebrate dies, its muscles stiffen as they are deprived of ATP, a state called rigor mortis. Explain the molecular basis for the rigor state.