Enzymes 3 2 Activation Energy Barrier Activation Energy

Enzymes 3. 2

Activation Energy Barrier • Activation Energy – initial investment of energy for starting a reaction (EA) • (energy needed to contort the reactant molecule) • Sometimes EA is transferred as heat • Also determines rate of the reaction (high EA, long)

Enzymes and EA • Enzyme – catalytic protein – Speeds it up by lowering the EA barrier

Substrate Specificity of Enzymes • Enzyme-substrate Complex – molecule resulting from an enzyme binding to its substrate (reactant)] • Enzymes are VERY specific and can recognized their substrate even among isomers – Due to shape of protein, which is consequence of amino acid sequence • Active Site – specific part of the enzyme that binds to the substrate

Local Conditions on Enzyme Activity • TEMPERATURE and p. H • COFACTORS – If organic, called coenzymes – helpers for catalytic reactions. Vitamins are a good example • ENZYME INHIBITORS – Competitive Inhibitors – mimics of the substrate that lower productivity by blocking substrates from entering active sites – Noncompetitive Inhibitors – bind to another part of the enzyme (not the active site) and changes shape of enzyme, so substrate cannot bind.

Regulation of Enzyme Activity • Allosteric Regulation – when a protein’s function at one site is affected by the binding of a regulatory molecule at a separate site (noncompetitive). – Could be inhibition or stimulation of enzyme activity

How Allosteric Regulation Works

Feedback Inhibition • When a metabolic pathway is switched off by the inhibitory binding of its end product