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