Enzymes

Let's Review: ΔG and rxn spontaneity

Let's Review: Protein Structure

Enzymes Biological catalysts Catalysts - chemical agent that speeds up the rate of a reaction without being consumed in the reaction Generally end in -ase Examples:  ATP synthetase  Sucrase

Activation Energy E A – the initial investment of energy for starting a chemical rxn.

Substrate Specificity Substrate – the reactant an enzymes acts on Enzymes binds to substrate and forms enzyme- substrate complex Active site – where the substrate binds the enzyme High specificity depends on enzymes 3-D conformation (shape of protein)

Induced fit As substrate enters active site, interactions b/n substrate's chemical groups & enzyme's aa's cause enzyme to change its shape to fit more snugly.

What affects enzyme activity? 1. Temperature - Up to a point, increasing temperature increases enzyme activity (why?) - After that point, enzyme denatures (protein loses correct conformation and becomes inactive)

2. pH - Enzymes have specific range for optimal activity - Ex: Pepsin (in stomach) works at pH = 2.0

3. Cofactors Cofactors – non-protein helpers for catalytic activity Ex: Inorganic: Zn, Fe, Cu ions Organic (called coenzymes): Vitamins Cofactors either bind permanently OR bind loosely/reversible

4. Inhibitors Competitive inhibitors – inhibitor mimics normal substrate and thus competes for a spot in the active site Overcome by adding more substrate Example: CO & Hemoglobin

Noncompetitive inhibitors – bind to another part of enzyme and cause change in enzymes conformation (shape) thus making the active site less effective Ex: Penicillin and bacterial cell walls

Regulation of Enzyme Activity Allosteric Regulation – occurs when a proteins function at one site is affected by the binding of a regulatory molecule at a separate site. Most enzymes are composed of subunits that oscillate between two conformational states (active or inactive)  Binding of an activator causes conformation to switch to active  Binding of an inhibitor causes conformation to switch to inactive

Feedback Inhibition When a metabolic pathway is shut off by the inhibitory binding of its end product to an enzyme that acts early in the metabolic pathway