C485 Exam II Fall ‘12
Name___________________
Legible please!
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. (32 Pts total) Please answer the following questions about glycogen metabolism. Use
chemical structures where indicated.
a) 4 pts Draw the structure of the two different types of glycosidic linkages found in
glycogen.
b) 8 pts The breakdown of glycogen is highly regulated. Outline this regulation, taking
care to explain how the difference in function between the liver and the muscle dictates a
different strategy for regulation.
c) 6 pts Outline the steps involved in the breakdown of glycogen. Make sure to explain
the function of all enzymes involved and to show the structure of the reaction product.
d) 10pts Using structures and explanations, describe the steps involved in the synthesis
of glycogen via the Leloir pathway. Explain the energetics of the process and why the
nucleoside triphosphate is used as it is.
e) 4 pts What is meant by reciprocal regulation? Give an example associated with
glycogen metabolism.
2. (33pts total)
a) 13 pts There are two carboxylation reactions associated with the breakdown and/or
synthesis of fatty acids. Draw these two reactions and detail the mechanism of one of
them, making sure you show the role(s) of any cofactors involved.
b) 10 pts What molecule is responsible for ferrying nitrogen from muscle to the liver?
What becomes of this molecule in the liver? What happens to the nitrogen in this
molecule? Show the likely mechanism of this reaction.
c) 10 pts Vitamin B12-dependent reactions are important in the metabolism of odd
carbon fatty acids. Show the reaction involved, and draw the mechanism of the reaction.
3. (12 pts) What are the five steps associated with signal transduction? Describe the
first four of these steps for the signaling processes associated with glycogen breakdown,
and then glycogen synthesis. You must put these steps in order. (You may show
intermediate steps if you wish.)
4. (8 Pts) a) How many enzyme activities are required for attachment of ubiquitin to
target proteins? b) Draw the attachment site between ubiquitin and proteins that are
targeted for degradation. (You must show enough chemical structure so the nature of the
bond and the relevant residues involved in the bond can be identified.) Describe the
general process used by the proteasome to degrade these tagged proteins.
5. (8 Pts) Calculate the approximate yield in ATP molecules of the complete oxidation of
the C10 fatty acid shown below. (Show how you arrive at this number.)
6. (10 pts) Consider the degradation of threonine. Outline the intermediates that connect
the degradation of this molecule to a major biochemical pathway. Considering that this
process takes place in the liver, where does the nitrogen wind up?
7. (10 pts) Describe the organization of the fatty acid synthase. List four differences
between fatty acid synthesis and fatty acid degradation.
8. (7 pts) What are the two major sources of generating the reducing power used in fatty
acid synthesis. One of these processes involves no net oxidation or reduction. Explain
how this is possible.
Point breakdown
Possible
actual
1)
32
________
2)
33
________
3)
12
________
4)
8
________
5)
8
________
6)
10
________
7)
10
________
8)
7
________
TOTAL 120
__________