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Chem 142B
18 February 2004
MIDTERM II
NAME____________
Avagadro’s number, NA = 6.022x 1023
Faraday’s Constant, F = 96.5 kJ/V.mol
Gas Constant, R = 8.324 J/mol.K
1. What general type of reactions is catalyzed by each of the following prosthetic groups
(for full credit describe the class of reactions in words rather than by example).
a) Biotin
Biotin uses the energy available from ATP hydrolysis to activate carbon
dioxide for carboxylation reations.
b) Pyridoxal Phosphate
Activates groups attached to a primary amine; e.g. for removal of the amino
group in aminotransferases.
c) Tetrahydrofolate
Stores and delivers one carbon units such as methyl groups, methylene groups
and formyl groups.
d) Cobaltamine
Catalyzes radical rearrangements in mutates.
2. You’re on the Atkins diet and thus your body is catabolically metabolizing amino acids
for energy. During such catabolism the amino acid alanine is readily converted into
pyruvate. Would a mole of alanine or a mole of pyruvate (from glucose) provide more
energy? Argue your answer in terms of the cost/benefit of the conversion and of the
resulting nitrogen metabolism.
Alanine is deaminated to form pyruvate. Thus the two are energetically
equivalent save for the cost of discarding the nitrogen.
3. Cyanide binds to cytochrome oxidase (complex IV) abolishing electron transfer to
oxygen. It does not directly affect the other respiratory complexes, including complex I
(i.e. the complex that accepts electrons from NADH and pumps 4 H+ across the
membrane). And yet, cyanide fairly rapidly shuts down all of oxidative phosphorylation.
Why?
The electrons that should have gone to the oxygen stay in cytochrome C, such that
all of the cytochrome c becomes reduced. When all the cytochrome c is reduced,
it can no longer oxidize complex III and thus electron flow through complex III
(and the concomitant proton pumping) is abolished. And so on…
4. Fatty acids with an odd number of carbons require extra metabolic steps to metabolize.
a) Why?
The degradation pathway oxidizes the carbon beta to the carbonyl,
removing two carbons at a time. If the beta carbon is the terminal carbon
(as it would be for the last round of oxidation of a 3 carbon FA), this
oxidation would produce a formal group, which is cannot be cleaved by
thiolase from the FA chain.
b) Draw the additional pathway. Show all substrates and products.
See page 609 of your text.
5. Here are several intermediates in the respiratory cascade and their redox potentials:
NADH, -0.32V; CoQ, 0.05V; Cytochrome C, 0.24V; 1/2O2 + 2H+ -> H2O, 0.82V
Given these values, how much free energy could be extracted to pump protons across
each of the respiratory cascade complexes listed below, and how does this number relate
to the actual number of protons pumped?
Complex I (NADH:ubiquinone oxoreductase)
Complex III (ubiquinone:cytochrome C oxoreductase)
Complex IV (cytochrome c oxidase)