C485 Exam I Fall ‘09
Do not use acronyms. Use structures whenever they are asked for, or appropriate. Your explanations should be brief. Overly lengthy answers with irrelevant or erroneous material will receive deductions. GOOD LUCK
1. (10 Pts) Consider enzyme catalysis completely from the perspective of binding. Name two strategies an enzyme could use to achieve catalysis. Draw a notional free energy profile depicting these. (You should draw a starting profile and then show what results when you apply the strategy you have selected.)
2. (4pts) What is the overall redox reaction catalyzed by PSll?
3. (4 pts) There are two mobile electron carriers in photosynthesis that carry electrons between the three major components (PSI, Cytochrome bf and PSII), please name them.
4. (8 pts) Draw the mechanism for how the mobile electron carrier between PSII and Cytochrome bf undergoes reduction (use chemical structures).
5. (6 Pts) Show the overall reaction for a complete photosynthetic process, showing both ATP production and NADPH production (start with two water molecules and absorb as many photons as necessary).
6. (8 Pts) Assign each function or product in the right column to the appropriate structure of pathway in the left column (you may need to assign multiple functions- each individual answer must be completely correct to get credit).
(a) chlorophyll ______(1) oxygen generation
(b) light harvesting complex ______(2) ATP synthesis
(c) photosystem I ______(3) light collection
(d) photosystem II ______(4) NADPH synthesis
(5) separation of charge
(6) light absorption
(7) transmembrane proton gradient
7. (10 pts) Rubisco contains an essential active site magnesium. Draw the relevant substrate contacts, as well as any special groups from the enzyme that make direct contact. Describe the chemical role of magnesium in promoting catalysis.
8. (10 Pts) Draw the unwanted competing side reaction catalyzed by rubisco (structures please). What is the ultimate fate of the abberant molecules produced in this process?
Why is this process referred to as photorespiration?
9. (10 Pts) Name and draw the chemically active portion of the essential cofactor used in two carbon transfer processes in the Calvin cycle and pentose phosphate pathway. Draw the mechanism of the reaction catalyzed by this cofactor. (You must use structures and curly arrows. You may use either the reaction from the Calvin cycle, or the pentose phosphate pathway.
10. (8 Pts) Name the two molecules that help regulate (not activate) the Calvin cycle? Explain the logic of how these molecules relate to photosynthesis.
11. (6 Pts) Which of the following statements about glucose 6-phosphate dehydrogenase are correct? (Just list by letter.)
(a) It catalyzes the committed step in the pentose phosphate pathway.
(b) It is regulated by the availability of NADP+.
(c) One of its products is 6-phosphogluconate
(d) It is important in the metabolism of glutathione in erythrocytes.
12. (6 pts) Match the enzymes that degrade glycogen in the left column with the appropriate properties in the right column. (More than one property may match. You need to get each answer completely correct for credit.)
(a) Phosphorylase ______(1) is part of a single polypeptide chain with two activities
(b) a-1,6-Glucosidase ______(2) cleaves a-1,4 glucosidic bonds
(c) Transferase ______(3) releases glucose
(4) releases glucose 1-phosphate
(5) moves three sugar residues from one chain to another.
(6) requires ATP
13. (5 Pts) Degradation of glycogen in the muscle and liver yield two different end products. Which is formed in the liver and which is formed in muscle? What enzyme is responsible for this difference? What is the energetic significance of this difference?
14. (5Pts) Show the reaction catalyzed by transaldolase. Structures please (mechanism not required).
Extra credit: 10 Pts. You must get this completely correct- no partial credit.
Answer the following questions about the enzymatic degradation of amylase, a linear a-1,4 polymer of glucose that is a storage form of glucose in plants.
Would phosphorylase act on amylase? Explain
Would the rates of glucose 1-phosphate release from an amylase molecule by phosphorylase relative to that from a glycogen molecule having an equivalent number of glucose monomers be equal? Explain
Point breakdown
Possible actual
1) 10 ______
2) 4 ______
3) 4 ______
4) 8 ______
5) 6 ______
6) 8 ______
7) 10 ______
8) 10 ______
9) 10 ______
10) 8 ______
11) 6 ______
12) 6 ______
13) 5 ______
13) 5 ______
EC) 10 ______
TOTAL 110