Chapter 13.1:
Bioenergetics and
Thermodynamics
CHEM 7784
Biochemistry
Professor Bensley
Introduction and Chapter 13.1
Bioenergetics and Thermodynamics
Today’s Objectives: To learn and understand the
– Differences between metabolic, catabolic,
and anabolic processes
– Thermodynamic applications to metabolic
processes
Bioenergetics and
Thermodynamics
• Bioenergetics – the quantitative study of
energy transductions (changes from one
form to another)
• First Law of Thermodynamics –
conservation of energy
• Second Law of Thermodynamics –
universe always tends towards increasing
disorder
Laws of Thermodynamics Apply
to Living Organisms
• In order to maintain organization within
the themselves, living systems must be
able to extract useable energy from the
surrounding, and release useless
energy (heat) back to the surrounding
(Open systems)
Mathematical Relationships
∆G = ∆H - T∆S
• Standard free-energy change (∆G0) – standard conditions
(298K, 1 atm, [1M] initial for both reactants and products)
• Biochemical standard state says that [H+] = 10-7 and [H2O]
= 55.5 M
• Physical constants based on biochemical standard state are
written with a prime such as ∆G’0 and K’eq
Mathematical Relationships
∆G’0 = -RT ln K’eq
Mathematical Relationships
• ∆G is a constant but ∆G’0 is a function of concentrations and
temperature
∆G = ∆G’0 + RT ln [C]c[D]d
[A]a[B]b
• Spontaneity of a reaction is determined by value of ∆G not
∆G’0
• Some thermodynamically favorable reactions do not occur at
measurable rates (combustion of firewood) so they need to
be catalyzed (enzymes)
Mathematical Relationships
• Standard free-energy changes are additive
in the case of two sequential reactions
• Because of this, the idea of coupling a highly
exergonic reaction to an thermodynamically
unfavorable one happens
• Example (Glucose 6-phosphate formation)
• Equilibrium constants are multiplicative in
the case of two sequential reactions
Hydrolysis
Reactions tend
to be Strongly
Favorable
(Spontaneous)
Complete Oxidation of Reduced
Compounds is Strongly Favorable
• This is how chemotrophs obtain most of their
energy
• In biochemistry the oxidation of reduced fuels with
O2 is stepwise and controlled
• Recall that being thermodynamically favorable is not the
same as being kinetically rapid