Biology (university) · Part 02
Enzymes and energy
How cells use energy, and how enzymes speed up and control chemical reactions.
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- MetabolismAll the chemical reactions in a living cell. Catabolic reactions break molecules down and release energy. Anabolic reactions build molecules up and use energy.
- ATPAdenosine triphosphate, the cell's short-term energy carrier. Removing its end phosphate releases usable energy and leaves ADP.
- Free energyThe energy in a system that is available to do work, written as G. A reaction is spontaneous if the change in free energy (delta G) is negative.
- Energy couplingUsing an energy-releasing reaction to drive an energy-needing one. In cells, ATP breakdown is usually the releasing reaction.
- EnzymeA protein (sometimes RNA) that speeds up a reaction by lowering its activation energy. It is not used up and does not change delta G.
- Active site and induced fitThe active site is the pocket where the substrate binds. In induced fit, the enzyme changes shape slightly around the substrate for a tighter grip.
- Enzyme kineticsHow reaction speed depends on substrate amount. Speed rises, then levels off at Vmax when every active site is busy. Km is the substrate level giving half of Vmax.
- Enzyme inhibitionCompetitive inhibitors bind the active site and block the substrate. Non-competitive inhibitors bind elsewhere and change the enzyme's shape. Extra substrate can overcome competitive inhibition only.
- Feedback inhibitionThe end product of a pathway switches off an early enzyme in that pathway. This stops the cell making more than it needs.