01 September 2010 (Peter J. Hollenbeck)
ENERGETICS & THERMODYNAMICS IN THE CELL
Read: Chap 3: 81-98; 104-14; panel 3-1;
Problems: 14-17; see Q3-14, Q3-17 in
Energy in Chemical Reactions
Equilibrium & Disequilibrium
Equilibrium is defined as the lowest energy state for a system or reaction.
reaction, such as:
A + B <=> C + D
will proceed spontaneously to an equilibrium state, at which there will be a
characteristic ratio of products to reactants, regardless of the concentrations, absolute
or relative, at which they start out.
So, for the reaction above, at equilibrium, the ratio
[C][D]/[A][B] is equal to a constant, called
We will return to this shortly.
(2) Living systems, such as cells, are in a state of DISEQUILIBRIUM with their
environment, and require a constant input of energy to maintain themselves in this
A cell at equilibrium is dead, dead, dead.
(3) We can measure the energy stored in a chemical disequilibrium: the farther we are
from equilibrium, the more potential energy is contained there.
Cells use energy to
create various disequilibria and then use the energy stored there to perform useful
To understand this, we first need to review a little bit of thermodynamics.
***In WHAT DIRECTION will events proceed in the cell?
***Do particular reactions CONSUME or PRODUCE energy?
First Law of Thermodynamics
- energy is neither created nor destroyed, but can change
The cell can be thought of as a machine that converts energy from one form to
Photosynthetic cells (e.g., in plants) convert the energy of sunlight into
All cells convert one form of chemical energy to another, and
convert chemical energy into heat and mechanical energy.
(2) For the cell, the pathway for energy conversion is critical!
You can use a flame to
burn glucose (C H O ) to yield CO and H O, releasing the energy of chemical bonds
as heat and light.
But when a cell “burns” glucose, also yielding CO and H O, it uses