Gibbs free energy (ΔG) is very important in biological systems because it tells us whether a process in the body can happen spontaneously and how much useful energy is available. Here’s a explanation:
1. Determining spontaneity of biochemical reactions
- Negative ΔG → reaction happens spontaneously.
- Positive ΔG → reaction requires energy input.
- Example: ATP hydrolysis
- ATP → ADP + Pi releases energy (ΔG < 0) → powers muscle movement, nerve signals, and biochemical reactions.
2. Coupling reactions
- Many biological reactions are non-spontaneous (ΔG > 0).
- Cells couple them with spontaneous reactions (like ATP hydrolysis) to make the overall process spontaneous.
- Example: Glucose phosphorylation in glycolysis requires energy but is coupled with ATP hydrolysis.
3. Metabolic pathways
- ΔG helps determine direction of metabolic reactions.
- Reactions flow spontaneously toward products that lower the free energy of the system.
- Example: Cellular respiration: Glucose → CO₂ + H₂O releases energy (ΔG < 0) → drives ATP production.
4. Phase and concentration effects
- ΔG depends on temperature, pressure, and concentration of reactants/products.
- Biological systems maintain concentrations and conditions to favor desired reactions.
- Example: Oxygen transport in blood: ΔG changes with oxygen concentration, helping oxygen release to tissues.
Summary
- Gibbs free energy tells which reactions are spontaneous in the cell.
- It helps couple energy-releasing and energy-requiring reactions.
- It guides metabolism, energy transfer, and cellular processes efficiently.