Bioenergetics Flashcards
Isolated System -
- Cannot exchange energy or matter with its surroundings
closed system
can exchange energy heat or work
open
can exchange both energy and matter
First law of thermodynamics
Energy can neither be created nor destroyed
but it can be changed from one form to another or transported from one region to another
Explanation of 1st law
- Deals with energy balance in a reaction but doesn’t say anything about the preferred direction of the reaction
- Energy before = energy after
The heat change of a reaction at constant pressure = the enthalpy change
^H = ^U + P^V
2nd law
Any spontaneous process must cause
the entropy of the Universe to increase:
DSsystem + DSsurroundings = DSUniverse > 0
Entropy (S) is
A state function that
measures the degree of disorder or randomness of a system
2nd law equation and explaination
S = K loge W
- K = boltman constant
- W = ways of arranging system
- 2nd law : Spon change occurs in a direction that increases the combined entropy and the system and surroundings
Gibbs free energy
- The general condition for a process to occur spontaneously at constant temperature and pressure is
^G = ^H -T^S
Temp in kelvin
Value of delta G related to favourability
Delta G > 0 unfavourable – endergonic
Delta G = 0 equilibrium
Delta G < 0 favourable – exergonic
Gibbs free energy, G, is at what value at equilibrium??
minimum at equilibrium
What does ^G indicate?
indicates the thermodynamically preferred direction of a reaction, but not the rate at which the reaction proceeds
What determines the favourable direction?
For all chemical and physical processes, the interplay between DH and TDS
Factors that affect ^G
- Alter concentrations
2. Couple reactions
When all concentrations are 1 M
^G = ^G0
Key equation 3
DGº = –RT ln Keq
Key Equation 2
^G = ^G + RT loge [C]c[D]d / [A]a[B]b
What properties of ATP make it the major energy currency of biochemical processes?
- Relatively negative DG of ATP hydrolysis due to highly charged ATP polyphosphate group:
- relief of electrostatic repulsion
when terminal phosphate bond is
hydrolysed; - inorganic phosphate (Pi) undergoes
stabilisation as a resonance hybrid.
What properties of ATP make it the major energy currency of biochemical processes?
- ATP is thermodynamically unstable but kinetically stable – ATP hydrolysis has a high activation energy (200 to 400 kJ mol-1)
- Specific enzymes are required to catalyse phosphoryl group transfer
- The cell can therefore regulate the distribution of energy carried by ATP by regulating enzymes that act on ATP
With thermodynamics, one cannot determine
the speed of a reaction.
