1. ENYMES
IB Biology
Lecture 2

2. An enzyme is a catalytic PROTEIN
What is an Enzyme?
An enzyme is a catalytic PROTEIN
It is effective in small amounts
It is unchanged by the reaction
It speeds up the rate of reaching equilibrium in a reversible reaction

3. Lock and Key Hypothesis
Due to its precise shape and distinctive chemical properties, each enzyme is specific for a certain substrate or a VERY small group of substrate molecules.

4. Induced Fit Hypothesis
Some enzymes change shape when combined with a substrate
The active site is then molded into a precise conformation
The bonds of the substrate are stretched to make the reaction easier (less energy needed)

5. Enzyme changes shape after it connects with the substrate.

6. Three factors that affect the rate of enzyme-catalyzed reactions
Temperature—As temperature increases, molecules are moving faster and are more likely to collide and react.
Different enzymes have different optimum temperatures (ex: bacteria in hot springs, plants of the tundra, enzymes in our bodies)

7. Substrate Concentration
Increasing the amount of substrate will speed up the rate of reaction.
However, there comes a point when there is more substrate than enzyme so adding more substrate molecules will no longer increase the rate of reaction

8. pH—each enzyme has a range of PH in which it functions efficiently

9. Denaturation
Denaturation is a structural change in a protein that alters its 3-D shape and causes the loss of its biological properties

10. Denaturation may be cause by changes in temperature and pH
Heat—exposure to heat causes atoms to vibrate violently and this disrupts bonds within globular proteins, and causes changes in the chemical characteristics—usually the change is irreversible (ex: raw vs. cooked egg white)
pH—small changes in pH also alter the shape of proteins. However the structure MAY re-form when optimum pH is restored

11. Industrial uses of enzymes

12. Lactose-Free Milk The enzyme lactase helps digest lactose in milk
Many adults do not produce lactase, so drinking milk causes diarrhea and/or gas
Lactose-free milk can be produced using lactase
Whole-cell preparations may not be appropriate for food
Adding and removing enzymes to each product is expensive

13. So immobilized enzymes are used to make the milk

14. Methods of immobilizing enzymes

15. Metabolism consists of chains (linear sequences) and cycles of enzyme-catalzyed reactions

16. Metabolism=anabolic reactions + catabolic reactions
Anabolic reactions—larger molecules built from smaller molecules (ex: protein synthesis)—ENERGY REQUIRING/ ENDOTHERMIC
Catabolic reactions—larger molecules are broken down (ex: digestion)—ENERGY RELEASING/ EXOTHERMIC

17. Enzymes lower the activation energy of exothermic reactions

18. Competitive Inhibition
Example: Carbon dioxide should combine with Rubisco during photosynthesis but can be competitively inhibited by oxygen

19. Non-competitive Inhibition
Example: Nerve gas, Sarin blocks acetyl cholinesterase in synapse transmission

20. Allosteric Enzymes Allosteric enzymes have 2 sites.
Active site of the enzyme
Additional site where another substance can lock in
When the other substance is locked in, the active site is non-functional

21. End Product Inhibition—a specific type of Allosteric Inhibition
As the end product accumulate, the steps in the product are stopped