1.7 Enzymes

SBI4U

Macromolecule Enzymes

Macromolecule Enzymes

• Protease: Protein digesting

• Lipase: Lipid digesting

• Carbohydrases: Carbohydrate digesting

  • Eg. Amylase: Starch digesting

What are enzymes?

• Specialized protein

• Catalyst: Speed up chemical reactions

• Recycle to be used repeatedly

• Generally end in -ASE

Enzymes: 5 Characteristics

1. Don’t make anything happen

   • Chemical reactions would happen regardless, they just speed them up

   • Helps go from reactants → products

2. Not used up

3. Only needed in small amounts

4. Specific to substrate

   • This is why cell needs around 4000 enzymes to function

5. Chemically recognize, bind to, and modify substrates

Enzyme Activity: What happens to active site?

• Active site matches 3D shape — usually a groove/pocket inside enzyme

• When substrate binds to active site, enzyme-substrate complex formed

• Substrate → Product

  • Eg. Substrate = Maltose, Enzyme = Maltase, Product = 2 Glucose Molecules

• Active site reforms to be used again

Induced Fit Model

• Substrate DOES NOT EXACTLY FIT into active site

  • Previous ‘lock-and-key’ theory didn’t explain why the reaction occurs

• BOTH substrate and active site change shape when enzyme-substrate complex is formed

  • Bends/weakens chemical bonds holding substrate together

• Enzyme can also change local conditions WITHIN active site (does not affect enzyme or cell as a whole)

  • Eg. Change in: pH, water concentration, charge, etc.

Activation Energy: How do enzymes work?

• Activation Energy = energy barrier

  • EVERY cell needs to overcome activation energy to create reaction

  • Analogy: Rolling boulder up a hill

    • Person pushing = Cells

    • Boulder = Chemical reaction

    • Hill = Activation energy

• Low Activation Energy: End product has LESS energy than starting substance

  • Substrate naturally wants to lose energy = turns into product

  • Enzymes lower activation energy to speed up reaction

    • Lowering the hill

• High activation energy = slower reaction

  • Larger the hill = more energy needed to push upwards

• SUPPLY & DEMAND: Is both the substrate and active site available?

Co-Enzymes

• Organic molecules

• Required by certain enzymes to catalyze

• Binds to active site, but not considered substrate

• Involved in transfer of electrons (Coupled Oxidation/Reduction reactions)

• Comes from vitamins

  • Eg. NAD derived from Vitamin B-3

  • Low energy may mean low metabolism → take B vitamins

Co-Factors

• Inorganic substances

• Increase rate of catalysis

• Usually metallic ions

2 Main Factors Affecting Enzyme Activity

• Optimum: Optimal temperature and pH for enzymes to function

• Rate of reaction increases until optimum, then decreases until denaturation

Factors Affecting Enzyme Activity: Temperature

Temperature increase → Kinetic energy increase → Likelihood of molecules bumping into each other increase → Likelihood of substrate binding increase

• Too hot = 3D structure and bonding compromised → folding patterns lost → denaturation

  • Irreversible, cells will have to make new enzymes

• Too cold → Kinetic energy decrease

• Optimum: 37℃

Factors Affecting Enzyme Activity: pH

• Enzymes sensitive to acidity (presence of protons)

• Too low/high → chemical bonds rearranged → mis-folded → denature

• Optimum: 7-8 (in small intestine)

  • 2-4 (in stomach: pepsin, tripsin)

Enzyme Concentration

Increase enzyme concentration = Increase rate of reaction

• Chance of collision increase = higher likelihood of binding to substrate

• UNTIL saturation point: too many enzymes/active sites, not enough substrate

• Decrease enzyme concentration = Decrease rate of reaction

Substrate Concentration

Increase substrate concentration = increase rate of reaction

• Chance of collision increase = higher likelihood of binding to active site

• UNTIL saturation point: too much substrate, not enough enzymes/active sites

  • ONLY happens in LAB setting

  • In the body, ALWAYS MORE SUBSTRATE THAN ENZYMES

What are inhibitors? Where are they found?

• Reduce rate of reaction

• Prevents growth of unwanted substances by preventing substrate from binding to active site

• Found naturally and synthesized

• Eg. Drugs, pesticides, etc.

Competitive Inhibition

• Molecule similar in structure to substrate

• Can fit into active site

• In competition with substrate to bind with active site = slows down reaction

• To reverse: Increase substrate concentration

  • If inhibitor concentration too high → outcompete substrate

• Eg. CO competes with O2 for hemoglobin active site

Non-Competitive Inhibiton

• Different in structure to substrate

• Cannot bind to active site

  • Binds to allosteric site

• Induced change in enzyme shape → change active site shape → substrate no longer fits

• Reduce enzyme activity

  • Waste of energy if nutrients aren’t needed by cells

• Eg. DDT (pesticide)

  • Irreversible

  • Inhibit bird nervous system → passes to chicks → soft egg shell

  • Banned

Feedback Inhibition

• End product acts as inhibitor for starting product

• Binds to allosteric site, inhibiting enzyme activity (non-competitive inhibitor)

  • Creates high/low affinity for substrate

• Reversible

• Ensures cellular resources aren’t wasted

Feedback Inhibition: Isoleucine Example

If isoleucine concentration decreases → threonine binds to enzyme 1 → continues pathway

(High Affinity State) If isoleucine concentration too high, it acts like non-competitive inhibitor

• Binds to enzyme 1 → prevent threonine from binding → shut down pathway

• (Low Affinity State) Too much isoleucine used as inhibitor → concentration decrease → cycle continues (Back to High Affinity)