CHEM 3653: AC4 Problems

The following question is offered in anticipation of our chapters on metabolism: Assuming that the average weight of an adult is 180 lbs, how many molecules of oxygen arrive each second at a mitochondrion of an average active person? Assume that oxygen consumption is 43 mL per minute per kilogram of body weight, adults have about 1.0 x 1012 cells, and there are 900 mitochondria per cell. Report your answer to seven figures.

about 1.75 × 10⁶ O₂ molecules/second/mitochondrion

Two structures of glycine can be drawn that have a net charge of zero, but the predominant form of glycine at its pI is zwitterionic. Why is glycine predominantly zwitterionic rather than completely uncharged at its pI? What percent of glycine molecules would be in the completely uncharged form at the pI?

Explain why gelatin, which is mostly collagen, is nutritionally inferior to other types of protein.

Radioactively labeled [14 C]-proline is incorporated into collagen in cultured fibroblasts. The radioactivity is detected in the collagen protein. But collagen synthesized in the presence of [14 C]-hydroxyproline is not radiolabeled. Explain why.

Approximately how many grams of monosodium succinate (FW = 140 g/mol; succinic acid pK2 =5.64) and disodium succinate (FW = 162 g/mol) must be added to water to produce a 1-L solution that has a pH of 6.18 and a total solute concentration of 100 mM. (Answer in grams monosodium succinate, grams disodium succinate)

3.13 g monosodium succinate + 12.57 g disodium succinate

A compound has two carboxyls and one amino group. The pKa s of the groups are 1.8, 4.2, and 9.1, respectively. A biochemist has 80 mL of a 0.14 M solution of this compound at a pH of 4.9. She adds 25 mL of 0.12 M NaOH. What will be the final pH of the solution after the addition of the NaOH? Report answer to two significant figures.

pH = 8.2

Which set of binding data (Set A or Set B) is likely to represent cooperative ligand binding to an oligomeric protein? You may want to graph the data to help you answer the question. Write “A” or “B” to indicate your answer or “C” for neither set.

Set B

Use the equation shown below to make the following calculations. Calculate Y in the lungs when p50 = 24 torr, n = 3.1, and pO2 = 100 torr. Then calculate Y in the capillaries, where pO2 is 25 torr, n = 3.1, and p50 = 24 torr. What is the overall efficiency, which is the difference (expressed as a percent) between the fractional saturation in the lungs minus the fractional saturation in the tissues?

Lungs: Y = 0.988; tissues: Y = 0.532; efficiency = 45.7%

Use the same values reported for the problem above, but this time let n=1 instead of 3.1. Calculate Y in the lungs, Y in the capillaries. What is the overall efficiency, which is the difference (expressed as a percent) between the fractional saturation in the lungs minus the fractional saturation in the tissues?

Lungs: Y = 0.988; tissues: Y = 0.532; efficiency = 45.7%

Protein A has a binding site for ligand X with a Kd of 10 ^-6 M. Protein B has a binding site for ligand X with a Kd of 10 ^-9 M. Which protein has a higher affinity for ligand X? Why? Hint: You may want to convert K_d to K_assoc for both proteins.

Protein B has higher affinity because its Kd is smaller. A: Kassoc = 10⁶ M⁻¹; B: Kassoc = 10⁹ M⁻¹

The protein calcineurin binds to the protein calmodulin with an association rate (k_on) of 8.9*10 ³ M ^-1 s^-1 and an overall dissociation constant Kd of 10 nM. Calculate the dissociation or off-rate (k_off), including appropriate units.

koff = 8.9 × 10⁻⁵ s⁻¹

An F_ab fragment of an antibody binds to an antigen with a Kd of 5*10 ^-8 M. At what concentration of antigen will Y be 0.2? 0.5? 0.6? and 0.8?

Y=0.2: 1.25×10⁻⁸ M

Y=0.5: 5.0×10⁻⁸ M

Y=0.6: 7.5×10⁻⁸ M

Y=0.8: 2.0×10⁻⁷ M

While most humans are able to hold their breath for only a minute or two, crocodiles can stay submerged under water for an hour or longer. This adaptation allows the crocodiles to kill their prey by drowning. In 1995, Nagai and colleagues suggested that bicarbonate (HCO₃^–) binds to crocodile hemoglobin to promote oxygen dissociation in a manner similar to BPG in humans and, in so doing, promotes delivery of a large fraction of bound oxygen to tissues. Consider the hypothesis that bicarbonate serves as an allosteric modulator of oxygen binding to hemoglobin in crocodiles. What is the source of HCO₃^– in crocodile tissues?

Draw oxygen-binding curves for crocodile hemoglobin in the presence and absence of bicarbonate. Which conditions increase the p50 value for crocodile hemoglobin? What does this tell you about the oxygen-binding affinity of hemoglobin under those conditions?

The drug hydroxyurea can be used to treat sickle cell anemia, although it is not used often because of undesirable side effects. Hydroxyurea is thought to function by stimulating the afflicted person's synthesis of fetal hemoglobin. In a clinical study, patients who took hydroxyurea showed a 50% reduction in frequency of hospital admissions for severe pain, and there was also a decrease in the frequency of fever and abnormal chest X-rays. Why would this drug alleviate the symptoms of sickle cell anemia?

The bicarbonate buffer system of the blood is very efficient because

carbon dioxide is rapidly eliminated through the lungs.

Atoms are isotopes of each other only if

their atomic numbers are the same, but their mass numbers differ.

Absence of which of the following blood enzymes drastically reduces blood CO2 carrying capacity?

Carbonic anhydrase

Which of the following BEST explains why proteins are able to buffer physiologic solutions over a wide range of pH?

They contain many functional groups with differing pKs.

A physiologic buffer functions to

minimize the increase in hydrogen ion concentration that accompanies cellular acid production.

All of the following function in buffer systems in the blood EXCEPT

NaCl

The buffer system most important in maintaining the physiological pH of plasma is

carbonic acid/bicarbonate