BIO-ENERGETICS
Energy producing and energy utilizing
systems
Catabolic pathways –
generation of energy by transformation (glycolysis) or oxidation (oxidative
phosphorylation) of ingested or stored fuels.
Anabolic pathways –
utilization of energy for biosynthetic purposes (DNA synthesis, protein
synthesis, etc.)
C. ATP –
the link between the two pathways
1.
Phosphoanhydride bonds as high energy bonds
2.
Other nucleotides
(a)
GTP: gluconeogenesis and protein synthesis
(b)
CTP: lipid synthesis
(c)
UTP: glycogen synthesis
(d)
All depend on ATP formation: nucleoside diphosphate kinase
3.
Other bonds having a high free energy of hydrolysis (> 7 kcal/mole)
(a)
1,3 bis-phosphoglycerate (mixed acid anhydrides)
(b)
Phosphoenolpyruvate (enol phosphates)
(c)
Creatine phosphate (phosphoguanidines)
(d)
Pyrophosphate (phosphoric acid anhydrides)
(e)
Acetyl CoA (thiol esters)
Thermodynamic relationships and
energy rich compounds
A. Laws of
thermodynamics
First Law: energy
may be converted from one form to another, but the total in a
system remains constant. (Glucose ® lactate + ATP)
Second Law: Entropy
(DS) is a measure of disorder or
randomness of a system. All
systems tend to progress towards maximum entropy. Entropy is unavailable to
perform useful work.
Free energy (DG): available
for useful work
(a)
DG = DH – TDS
(DH =enthalpy, T = temperature in
degrees K)
(b)
Exergonic:free energy lost, spontaneous reaction (DG less than 0)
(c)
Endergonic:requires energy for reaction to proceed (DG greater than 0)
(d)
At DG = 0, the reaction is at
equilibrium
(e)
The actual free energy change (DG
for a reaction is equal to the standard free
energy (DGo’) plus a term tha depends on
actual concentrations of products
and reactants
DG’ =DGo’+
RTln{[Products]/[Reactants]}
DG’= DGo + 1.4 logP/ (in
kcal/mole)
Where DGo’ = –Rtln(Keq =
–1.4 log(Keq) (inkcal/mole)
Free energy changes for coupled reactions are ADDITIVE
DGo’ A + B ® C + D –5.0
D ® P + Q + 4.5
Sum of coupled rx A + B ® C + P + Q – 0.5
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