C485 Exam II Fall ‘10
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. (33 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) 6 pts There are three chemical reactions required to degrade glycogen. Using
structures and explanations show what these are.
c) 5 pts Place the following steps of the reaction cascade of glycogen metabolism in the
proper order:
a) activation of protein kinase A
b) formation of cyclic AMP by adenylate cyclase
c) phosphorylation of phosphorylase b
d) hormone binding to target cell receptors
e) phosphorylation of glycogen synthase a and phosphorylase kinase
first
_____
______
______
_______
______
last
d) 8pts Using structures and explanations, describe the steps involved in the synthesis of
glycogen via the Leloir pathway.
e) 5 pts Place the following steps of the insulin signaling cascade in the proper order:
a) Binding of phosphoinositide 3-kinase to SH2 domain
b) hormone binding and receptor dimerization
c) phosphorylation of Akt by PDK1 (PIP3-dependent protein kinase)
d) phosphorylation of IRS-1
e) receptor autophosphorylation
first
_____
______
______
_______
______
f) 5 pts What is meant by reciprocal regulation? Give an example associated with
glycogen metabolism.
last
2. (30pts total)
a) 10 pts Draw a mechanism for the conversion of methylmalonyl CoA into succinyl
CoA. If there is a cofactor involved, you must indicate a basic idea of the structure of
the cofactor and its involvement in the chemistry.
b) 10 pts Draw a mechanism for the conversion shown below. You may adjust
protonation states between steps so as to shorten your mechanistic scheme. If there is a
cofactor involved, you must indicate a basic idea of the structure of the cofactor and its
involvement in the chemistry.
c) 10 pts Draw a mechanism for the reaction catalyzed by AcetylCoA carboxylase. If
there is a cofactor involved, you must indicate a basic idea of the structure of the cofactor
and its involvement in the chemistry.
3. 16 pts Please answer the following short questions (4 pts each)
a) What are the two major sources of reducing power required for fatty acid synthesis?
b) How is pyrophosphatase involved in the activation of fatty acids for beta oxidation?
c) Explain the involvement of carnitine in the beta oxidation of fatty acids.
d) What two properties make triacylglycerols more efficient than glycogen for the storage
of energy?
4. 8 pts Please list four ways in which fatty acid biosynthesis is different than simply the
reverse of beta oxidation.
5. (7 pts) Match the items in the left hand column with the correct item(s) from the right
hand column. (Items in the right hand column may be used more than once.)
AMP_______
1) downregulates synthesis of malonyl CoA
Insulin_______
Palmitoyl CoA________
2) required cofactor for synthesis of malonyl
CoA
3) stimulates synthesis of malonyl CoA
Citrate________
4) is part of the acyl carrier protein
Pantetheine_______
5) stimulates production of cAMP
cAMP__________
6) essential cofactor for transamination
reactions
7) released by the pancreas to catalyze
peptide bond hydrolysis
Biotin__________
6. (7 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.)
7. (7 pts) a) 4 pts The two nitrogen atoms in urea are derived from amino acids. Which
amino acids are these? b) 3pts What is the carbon byproduct of the urea cycle and how is
this metabolized?
8. extra credit (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.)
9. extra credit (8 pts)
Nitrogen excretion via the urea cycle is an energetically costly process. Consider the
processing of the amino acid shown below. How many ATP equivalents are used to
process this amino acid via the urea cycle? How many ATP equivalents are obtained
from the carbon skeleton of the amino acid? What is the net production of ATP from this
molecule?
Point breakdown
Possible
actual
1)
33
________
2)
30
________
3)
16
________
4)
8
________
5)
7
________
6)
7
________
7)
7
________
EC8) 8
________
EC9) 8
________
TOTAL 124
__________