Biochem Block Final Exam, Free Response Questions (104 pts) Your Name______

Below you will find structures for several natural molecules and artificial sweeteners (labeled in red).

1. ( 24 pts) Comparing the structures of the artificial sweeteners (sucralose, aspartame and saccharin) to the other naturally-occurring molecules, which of these three do you think would appear to be most foreign to your body? Explain your answer, using your knowledge of weak interactions in biochemistry.

2. (14 pts) Taste receptors have 3-dimensional pockets that bind their ligands (in this case, the sugar or sugar analogue). Examine carefully the structures of table sugar (sucrose) and sucralose (found in Splenda), the latter being a sugar analogue where some of the hydroxyl (OH) groups have been replaced with chlorine (Cl).

A) Which monosaccharides (galactose, glucose, fructose) are used to make sucrose?

B) Which monosaccharides (galactose, glucose, fructose) are used to make sucralose?

C) Based on your knowledge of noncovalent interactions in biochemistry (hydrogen bonds, charge-charge, dipole-dipole, etc.), explain how sucralose might be able to bind to a taste receptor for sucrose.

3. (8 pts) Using your knowledge of the glucose oxidation pathways of glycolysis and the citric acid cycle, do you think sucralose will be metabolized/broken down in your body? Explain briefly. (Consider enzymes and weak interactions…)

Please feel free to make drawings and/or incorporate graphics from the handouts in your answers.

4. (10 pts) A bacterium is discovered on Mars. For energy, it breaks down the sugar mannose in a pathway similar to glycolysis. The enzyme Timburtonase is responsible for the 1st reaction of the pathway, involving phosphorylation of mannose.

A) What effect would you predict ATP to have on this enzyme? Explain your reasoning.

B) Quickly sketch the sigmoidal V vs [S] curve for the enzyme, and on the same graph draw a curve showing the effect of ATP.

5. (8 pts) Compare the two amino acids Ser and Val. Which one is more likely to be found on the outer surface of a folded protein? Which one is more likely to be found on the inside of the protein? Explain briefly.

6. (6 pts) The enzyme hexokinase is responsible for adding a phosphate group to glucose in the first reaction of the glycolysis pathway. It has a large cleft (cavity) which closes in to hug glucose tightly. Which of the two models for enzyme-substrate binding does this best correspond to? Explain briefly.

7. (10 pts) Hemoglobin, our oxygen transport protein, is very sensitive to conditions. On the same graph, draw oxygen binding curves for hemoglobin under the following conditions:

A) Hb @ pH 7.1

B) Hb @ pH 7.5

C) Hb @ pH 7.1 + BPG

Note that this is not a quantitative question – just draw the pH 7.1 curve first and show how the other changes will shift the curve.

8. (12 pts) Think back over the course and what you have learned in the past few weeks. Elaborate/discuss/draw something you found particularly interesting/beautiful and why you chose it.

9. (12 pts) I am interested in your feedback regarding the biochem block. Note: you will get full credit no matter what you write, so don’t worry!

A) What did you like most about this course?

B) What did you like least about this course?

C) Do you have any suggestions for how to improve the course?