Download Chapter14

Fundamentals of
Biochemistry
Third Edition
Donald Voet • Judith G. Voet •
Charlotte W. Pratt
Chapter 14
Introduction to Metabolism
Copyright © 2008 by John Wiley & Sons, Inc.
This final is going to be hard!!
Just kidding!!
Terms
•
•
•
•
•
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Catabolic – degradation
Anabolic – synthesis
Autotrophs – (Latin – self, feeder)
Heterotrophs (other, feeder)
Aerobes – use oxygen
Anaerobes – oxidize without oxygen
Thermodynamics
• Remember that ΔG°’ = -RT lnKeq
– Therefore, concentration is very important
– If reactants are close to equilibrium concentration, ΔG
will be zero.
• Therefore, both forward and reverse reactions can happen
equally.
• Not all reactions happen close to equilibrium
– Enzymes not close to equilibrium are irreversible
– If a pathway has ONE irreversible step, the entire
pathway is irreversible
Flux
• The rate of flow of metabolites through a pathway
– One step is always committed (irreversible)
• Remember, living things are at steady state, not equilibrium
• J(flux of metabolite) = vf - vr
– Rate of flux for irreversible step if rate of forward rxn
– Slowest step usually controls flux of a pathway
– Sometimes multiple enzymes control flux of pathway
• Control
–
–
–
–
Allosteric
Covalent modification
Substrate cycles
Genetic control
High-energy intermediates store energy to drive endergonic reactions
Phosphocreatine can transfer a phosphate to ADP
ATP + creatine ↔ phosphocreatine + ADP
ΔG°’ = 12.6 kJ/mol
Another high energy
bond is the thioester
bond. This is used in
carbohydrate, protein,
and fatty acid metabolism
with acetyl-CoA
Redox reactions
• The majority of energy is supplied via redox
reactions.
• Ultimately, oxidation results in the
movement of electrons to oxygen.
• This requires carriers of the electrons
Redox reactions can be
separated into half-cells
to create a battery.
Batteries do word,
therefore we can
calculate the work (or
free energy change) of
redox reactions
Aoxn   Bred  Ared  Boxn 
 
 
 Ared  Boxn  

G  G' RT ln  n 
 Aox Bred  
G   w'   wel
wel  nE
G  nE
 
 
RT  Ared  Boxn  
 n 

E  E ' 
n  Aox Bred  
NOTE: positive E results in -ΔG
Using Table 14-5, calculate the
free energy change for the
reaction
NADH + FAD + H+ → NAD+ + FADH2
Remember, electrons are transferred up
the table only.
Ways to Study Metabolism
• Labeling
– Nitrogen, Carbon, Sulfur
• Perturbing the System
– Disease states
• Systems Based
– Genome, transcriptome, proteome, metabolome
Labeling
Perturbing the system
1. Natural mutations
2. Inhibitors
3. Genetic manipulation
Systems Biology
Microarray analysis allows who genome analysis
Studying the proteome