2. THERMODYNAMICS OF LIVING SYSTEMS
43
Thus if AS X and AS 3 are known, AS for the reaction at T°K can be
easily calculated. The importance of knowing AS for a reaction is, that
if AH is determined, an experimentally feasible operation, the equation
provides a way of determining AF, and consequently the thermodynamic
equilibrium constant without requiring the measurement of a single
equilibrium state of the reaction itself.
In the pages to follow, AF will assume an important role in describing the energetics of living systems. If a particular process is
characterized by a large positive AF, it cannot be expected to go
spontaneously, but only if energy is added in an appropriate manner. If
AF is small, either positive or negative, the reaction may be made to
increase in one direction or the other by adjusting the ratio of the
products to the reactants. If AF has a large negative value the process
may be expected to go spontaneously to near completion. Once again,
it is noted that there is nothing implied about the rate associated with
a process characterized by a large negative AF.
A reaction which is accompanied by a decrease in free energy is
said to be exergonic, while a reaction which proceeds with ail increase
in free energy is termed endergonic. One way of getting energy into an
endergonic reaction would be to couple it with an exergonic one. The
only thermodynamic requirement for an exergonic reaction to drive an
endergonic one is that the exergonic reaction expend more free energy
than is gained by the reaction to be driven, requiring, of course, that
the entire process be exergonic. These types of reaction find great
utility in biological systems. A more complete discussion of the theory
of coupling of exergonic and exothermic reactions will be presented in
a later section.
K. ENERGETICS
1. Introduction
Living organisms, like any machine, require a constant source of
energy to keep them functioning. In terms of free energy, we may say
that some mechanism must be present to capture free energy and convert it into fuel which the organism may use. The major source of free
energy for our world is from the nuclear reactions taking place in the
sun. These reactions may be summarized by the equation
41H
1 -* 2 He
4 + 2,e° + hv
The term hv represents very hard gamma radiation which is absorbed
by electrons and re-emitted as smaller quanta. Eventually, after con-
43
Thus if AS X and AS 3 are known, AS for the reaction at T°K can be
easily calculated. The importance of knowing AS for a reaction is, that
if AH is determined, an experimentally feasible operation, the equation
provides a way of determining AF, and consequently the thermodynamic
equilibrium constant without requiring the measurement of a single
equilibrium state of the reaction itself.
In the pages to follow, AF will assume an important role in describing the energetics of living systems. If a particular process is
characterized by a large positive AF, it cannot be expected to go
spontaneously, but only if energy is added in an appropriate manner. If
AF is small, either positive or negative, the reaction may be made to
increase in one direction or the other by adjusting the ratio of the
products to the reactants. If AF has a large negative value the process
may be expected to go spontaneously to near completion. Once again,
it is noted that there is nothing implied about the rate associated with
a process characterized by a large negative AF.
A reaction which is accompanied by a decrease in free energy is
said to be exergonic, while a reaction which proceeds with ail increase
in free energy is termed endergonic. One way of getting energy into an
endergonic reaction would be to couple it with an exergonic one. The
only thermodynamic requirement for an exergonic reaction to drive an
endergonic one is that the exergonic reaction expend more free energy
than is gained by the reaction to be driven, requiring, of course, that
the entire process be exergonic. These types of reaction find great
utility in biological systems. A more complete discussion of the theory
of coupling of exergonic and exothermic reactions will be presented in
a later section.
K. ENERGETICS
1. Introduction
Living organisms, like any machine, require a constant source of
energy to keep them functioning. In terms of free energy, we may say
that some mechanism must be present to capture free energy and convert it into fuel which the organism may use. The major source of free
energy for our world is from the nuclear reactions taking place in the
sun. These reactions may be summarized by the equation
41H
1 -* 2 He
4 + 2,e° + hv
The term hv represents very hard gamma radiation which is absorbed
by electrons and re-emitted as smaller quanta. Eventually, after con-