BIOL 1010 Lecture Notes - Exergonic Reaction, Electronegativity, Redox
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Organism live at the expense of free energy
- The maximum amount of usable energy that can be harvested from a particular reaction is the
system’s free energy change from initial to the final state
- This change in free energy (ΔG) is given by the Gibbs-Helmholtz equation at constant
temperature and pressure: ΔG= ΔH-TΔS
An energy profile of a reaction
Comparison of passive and active transport
- In passive transport, a substance diffuses spontaneously down its
concentration gradient with no need for the cell to expend energy.
- Hydrophobic molecules and very small uncharged polar molecules
diffuse directly across the membrane.
- Hydrophilic substances diffuse through transport proteins in a process
called facilitated diffusion
- In active transport, a transport protein moves substances across the
membrane “uphill” against their concentrations gradients
- Active transport requires an expenditure of energy usually supplied by
An electrogenic pump
- Proton pumps are examples of membrane proteins that store energy by generating voltage
(charge separation) across substances
- Using ATP for power, a proton pump translocates positive charge in the form of hydrogen ions.
- The voltage and H+ gradient represent a dual energy source that can be tapped by the cell to
drive other processes, such as the uptake of sugar and other nutrients.