Download C485 Exam I

C485 Exam II Fall ‘14
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. (15 Pts total) Please answer the following questions about glycogen metabolism. Use
chemical structures where indicated.
a) 8 pts How many enzymatic activities are required for glycogen synthesis? Briefly
explain each one. 4
UDP glucose pyrophosphorylase takes UTP and G1-P to UDP glucose and
pyrophosphate
Glycogenin makes primers by taking UDP glucose and adding it to a tyrosine residue. It
then elongates by three more residues before synthesis can be taken over by glycogen
synthase.
Glycogen synthase elongates the chain by reaction between the 4-OH of the nonreducing
end of the polymer with UDP glucose to make the alpha 1,4 linkage.
Branching enzyme transfers blocks of (usually) seven residues to an internal C-6 OH of
the chain. Must be at least 4 residues away from an existing branch. Tends to make
branches on average of every 10 residues.
b) 3 pts What is meant by reciprocal regulation? Give an example associated with
glycogen metabolism.
When one molecule, or action turns on one pathway, while turning off the pathway that
carries out the opposing activity.
There are several of these. Protein kinase A is a good example. It activates glycogen
degradation by activating phosphorylase kinase, which converts phosphorylase b to
phosphorylase a. It also turns off glycogen synthase by phosphorylating it, thus
inhibiting glycogen synthesis.
c) 4 pts Draw the mechanism of glycogen cleavage catalyzed by the relevant enzyme.
Figure 21.7 pg 619
2. (21 pts) Pick a branched chain amino acid. Draw the pathway for its degradation.
Draw the mechanisms of the first two steps of this pathway.
See branched chain amino acid handout on website.
3. (12 pts) What are the five general steps associated with signal transduction? Briefly
describe (a) the hormone process that initiates the breakdown of glycogen; (b) the
hormone process that stimulates the synthesis of glycogen and absorption of glucose. A
good diagram for each will be useful.
Release of primary message
Reception of primary message
Release/activation of secondary messenger (message)
Activation of effector
Termination.
See figures 21.16 and 14.21
4. (10 Pts) What tag is used to label proteins for degradation? Show the first enzymatic
reaction used to activate and form this tag. Comment on the energy requirements for this
reaction. Why is this necessary?
See figure 23.3. This reaction requires the equivalent of 2 ATP cleavages (ATP goes to
AMP and 2Pi) because you are making a thioester bond, which is energetically higher in
energy than a phosphate anhydride. If you just used a terminal phosphate to activate, the
reaction would be driven backwards by the relatively high [Pi]. Coupling rxn to
pyrophosphate hydrolysis makes it functionally irreversible.
5. (18 Pts) List all the enzyme activities (including transport) required to degrade the C14
fatty acid shown below (either show the reaction at least once, or describe it). Calculate
the approximate yield in ATP molecules of the complete oxidation of this molecule.
(Show how you arrive at this number.)
CATI, translocase, CAT II, acyl CoA synthetase, acyl CoA dehydrogenase, enoyl CoA
hydratase, hydroxyl Acyl CoA dehydrogenase, thiolase, isomerase.
C14, so six round of oxidation and 7 AcCoA.
Each round of oxidation makes 4 ATP (2.5/NADH and 1.5 QH2)
10 ATP for each AcCoA. Subtract 1.5 ATP because one double bond already there.
Subtract two more for synthesis of thioester.
7X10 +6X4 – 1.5 -2= 90.5
6. (12 pts) What are the differences between fatty acid synthesis and breakdown? Given
these differences, how does the cell provide AcCoA for synthesis? How does it produce
the required reducing equivalents? Be specific and show relevant reactions (structures).
See list on page 657.
Figure 22.29. You must use structures for full credit.
7. (6 pts) Describe how allosteric affects are used to regulate glycogen breakdown in
muscle. Explain why this makes sense given normal energy utilization in muscle.
Fig 21.12 and text explanation immediately above (pg 622)
8. (6pts) Outline the degradation pathway for proline.
Fig 23.26
9) (16 pts) Odd carbon number fatty acids leave a breakdown product that is different
than that formed from even number fatty acids. What is it? Show how this can be
converted into something that can enter a primary metabolic pathway. Draw the
mechanism of this/these steps.
Propionyl CoA to succinyl CoA. Biotin dependent carboxylation. B12-dependent
rearrangement
10. (12 pts) super duper extra extra credit. It is often said that the urea cycle is coupled to
the Krebs cycle. In what way are these two pathways coupled? Why might this be
advantageous, and how does that explain the source of at least one of the nitrogens in
urea?
The urea cycle generates fumarate, which is converted by the TCA cycle into OAA.
OAA is converted back to Asp by transamination with Glu. Thus the alpha amino group
of Asp actually comes from glu. The other nitrogen on urea also comes from Glu. So
there are two points of contact between the Krebs cycle and the urea cycle which make
and regenerate Asp, which is the proximate amino donor. In a sense the Krebs cycle
regenerates the need cofactor “Asp” for the use of the cycle and helps it to incorporate the
amino group for glu, via transamination with OAA.
Point breakdown
Possible
actual
1)
15
________
2)
21
________
3)
12
________
4)
10
________
5)
18
________
6)
12
________
7)
6
________
8)
6
________
9)
16
________
10)
12
________
TOTAL 128
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