Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

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Enzymes

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Transcript of Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

Page 1: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

Enzymes

Page 2: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

Let's Review: ΔG and rxn spontaneity

Page 3: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

Let's Review: Protein Structure

Page 4: 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

Page 5: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

Activation Energy E

A – the initial investment of energy for starting a

chemical rxn.

Page 6: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

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)

Page 7: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

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.

Page 8: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.
Page 9: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.
Page 10: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

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)

Page 11: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

2. pH

- Enzymes have specific range for optimal activity

- Ex: Pepsin (in stomach) works at pH = 2.0

Page 12: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

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

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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

Page 14: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

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

Page 15: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.
Page 16: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

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

Page 17: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.
Page 18: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.
Page 19: Enzymes. Let's Review: ΔG and rxn spontaneity Let's Review: Protein Structure.

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