Bioenergetics - basics
Energy sources, types of work and heat in the living systems. Electrochemical potential, free energy and direction of processes
Bioenergetics is concerned with the process of energy transformation in living systems, as well as with the energetics of biochemical reactions (formation and breaking of chemical bonds in the biological molecules).
Energy source:
Animals: Food (chemical energy) → Oxidation → Electron transport chain (mitochondria) → Proton gradient (H+ pump) → ATP Synthesis → Metabolism
Plants: Sun light → Electron transport chain (thylakoid membranes) → Proton gradient (H+ pump) → ATP synthesis, sugars etc. → Metabolism
Living organisms are not heat engines. Instead they use rich in energy chemical compounds to support their state and life functions. All processes in living systems proceed at virtually constant temperature.
Types of work and heat
- Chemical work: building molecules such as proteins and nucleic acids.
- Osmotic work: moving substances against their concentration gradient.
- Electrical work: moving ions against a potential difference.
- Mechanical work: muscle contraction and cell movement.
Part of the energy is always released as heat. It helps keep body temperature steady, but it cannot be turned back into work at constant temperature.
Electrochemical potential
The electrochemical potential is the free energy per mole of a charged substance. It combines a concentration term and an electrical term:
An ion moves spontaneously from a higher to a lower electrochemical potential. There is no net movement when the two sides are equal.
Free energy and the direction of processes
- ΔG negative: the process is spontaneous (exergonic).
- ΔG positive: the process needs energy from outside (endergonic).
- ΔG zero: the system is at equilibrium.
Cells drive endergonic reactions by coupling them to exergonic ones, most often ATP hydrolysis.