1. ENZYMES and METABOLIC REACTIONS

2. How do reactions occur in cells? –Molecules are in constant motion –Collisions between molecules allow reactions to occur

3. ENZYMES and METABOLIC REACTIONS How do reactions occur in cells? –Molecules are in constant motion –Collisions between molecules allow reactions to occur How do we speed up reactions in cells?

4. ENZYMES and METABOLIC REACTIONS Enzymes –Are protein catalysts that allow chemical reactions to take place in our body without increasing the temperature –End with the suffix ‘-ase’

5. ENZYMES and METABOLIC REACTIONS Enzymes –Are protein catalysts that allow chemical reactions to take place in our body without increasing the temperature –End with the suffix ‘-ase’ –Examples: urease, amylase, sucrase

6. Catalysts Control the speed of reactions without changing the products formed –By reducing the activation energy

8. Catalysts Control the speed of reactions without changing the products formed –By reducing the activation energy –Tunnel vs. Climbing a mountain Remain unchanged and can be used over and over Often only needed in small amounts

9. Enzymes… Work on molecules called the substrate –Can be anything

10. Enzymes… Work on molecules called the substrate –Can be anything Are substrate-specific

11. Enzymes… Work on molecules called the substrate –Can be anything Are substrate-specific Alter the substrate in some way Examples:

12. Substrate approaches an enzyme The enzyme- substrate complex is formed Reaction is complete. Enzyme remains unchanged. Products are formed.

13. Enzymes Models Where the substrate joins the enzyme is called the active site ‘Lock and Key Model’ –The active site of an enzyme is a perfect match to a specific substrate

14. Enzymes Models ‘Induced-Fit Model’ –The active site changes shape slightly when the E-S complex join together –Makes a tighter fit

15. Factors that Affect Enzymes What happens at cooler temperatures? 1. Temperature –Reaction rates increase as temperature increases –Peaks at ~ 37 - 40°C then drops rapidly –Why? E.g. egg frying

16. Factors that Affect Enzymes 2. pH –Enzymes function within an optimal pH range Stomach pH Small intestine pH

17. Factors that Affect Enzymes 3. Concentration of Substrate Molecules –Reaction rate increases as the substrate concentration increases up to a point –Animation linkAnimation link –The limiting factor in the reaction may be the amount of substrate or the amount of enzyme available

18. Factors that Affect Enzymes 4. Inhibitor molecules –Molecules that attach to the enzyme and reduce its ability to bind substrate –There are two types of inhibitors: a.Competitive inhibitors b.Non-competitive inhibitors

19. 4. Inhibitor molecules a.Competitive inhibitors Attach to enzyme’s active site Shape is similar to substrate Compete with the substrate Often the end product of the reaction E.g. drugs and poisons - CO - Cyanide

20. 4. Inhibitor molecules a.Non-competitive inhibitors Attach elsewhere on the enzyme (not the active site) Attachment changes the 3D shape of enzyme Reaction still occurs, but is inhibited

21. Regulation of Enzyme Activity Feedback Inhibition –AnimationAnimation –Turns the path ‘off’ –Prevents accumulation of products –Final product of pathway interferes with an enzyme by binding with allosteric (regulatory) site and altering the active site

22. Regulation of Enzyme Activity Precursor Activity –AnimationAnimation –Turns the path ‘on’ –A substrate binds with the last enzyme in a path improving the fit of the E-S complex –Binds to the allosteric site –Speeds up the final product formation

23. Regulation of Enzyme Activity Both feedback inhibition and precursor activity are called allosteric activity Handout