Review Session

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Review Session

• Saturday, 3 pm PH 104

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Figure 25-17 Problems in the oxidation of
unsaturated fatty acids and their solutions.
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Figure 25-18 Conversion of propionyl-CoA to
succinyl-CoA.
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Figure 25-19 The propionyl-CoA carboxylase
reaction.
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Figure 25-20 The rearrangement catalyzed by
methylmalonyl-CoA mutase.
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Figure 25-21 Structure of 5-deoxyadenosyl-coba
lamin (coenzyme B12).
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Figure 25-23 Proposed mechanism of
methylmalonyl-CoA mutase.
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Figure 25-25 Ketogenesis the enzymatic
reactions forming acetoacetate from acetyl-CoA.
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Figure 25-28 A comparison of fatty acid ?
oxidation and fatty acid biosynthesis.
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Figure 25-29 The phosphopantetheine group in
acyl-carrier protein (ACP) and in CoA.
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Figure 25-30 Association of acetyl-CoA
carboxylase protomers.
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Figure 25-31 Reaction cycle for the biosynthesis
of fatty acids.
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Figure 25-32 The mechanism of carboncarbon
bond formation in fatty acid biosynthesis.
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Chapter 27, Nitrogen Metabolism 1.
Deamination 2. Urea cycle 3. Conversion of aa
carbon skeletons to common intermediates.
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First reaction in aa breakdown is always the
removal of the ?-amino group. Most are
transaminated to ?-KG which then transaminates
OAA to asp. Transaminases require PLP (vit
B6). Actual deamination to ammonia occurs via
glu DH.
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Figure 26-1 Forms of pyridoxal-5-phosphate.(a)
Pyridoxine (vitamin B6) and (b)
Pyridoxal-5-phosphate (PLP) (c)
Pyridoxamine-5-phosphate (PMP) and (d) The
Schiff base that forms between PLP and an enzyme
?-amino group..
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Figure 26-2 The mechanism of PLP- dependent
enzyme-catalyzed transamination.
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Nucleophillic attack by aa-NH3 on Schiff
base. E-Lys now free to act as general base.
Tautomerization encouraged by removal of the ?H
of aa by E-Lys and protonation of PLP
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(see animated figure)
Step II Conversion back to PMP requires reverse
of these 3 steps
An electron pushers delight Cleavage of any
of the aas C? bonds produces a resonance
stabilized carbanion whose e- are delocalized
onto PLP (the electron sink).
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Figure 26-3 The glucosealanine cycle.
Muscle aminotransferases accept pyruvate as their
amino acceptor. Overall scheme transfers
nitrogen to liver for urea cycle.
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Figure 26-4 The oxidative deamination of
glutamate by glutamate DH.
GluDH is allosterically inhibited by GTP and
NADH Activated by ADP, leu, and NAD.
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Nitrogen Excretory Products Ammonia Uric
Acid Urea
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Figure 26-7The urea cycle.
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Figure 26-8 The mechanism of action of CPS I.
Allosterically activated by N-acetyl glu
produced by NAGlu synthase--it is a sensor for
glu.
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Hi glu means lots of aa breakdown.
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Figure 26-9 X-Ray structure of E. coli carbamoyl
phosphate synthetase (CPS).
Small subunit
3 sites very far away from each other Connected
by long tunnel Channeling!
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Ornithine Transcarbamoylase
Carbamoyl Phosphate Ornithine ? Citrulline Pi
Ornithine produced in the cytosol must be
transferred to mito by specific transport
system. Citrulline is transferred back out to
the cytosol Ornithine looks like Lys but has one
fewer Cs
Thus the side chain amino group is
? !!!!
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Figure 26-10 The mechanism of action of
argininosuccinate synthetase.
Displacement
Activation
18O label Mechanistic support
Reaction type?
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Condensation
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Arginosuccinase Arginosuccinate ? Arg Fumarate
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Arginase Arg H2O ? Ornithine Urea
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Figure 26-11 Degradation of amino acids to one of
seven common metabolic intermediates.
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