Limiting factors

1. Limiting factors Factors affecting the rate of reactions

2. EFFECT OF SUBSTRATE CONC. ON REACTIONS Substrate concentration Enzyme limiting More substrate  more chance of a collision between substrate and enzyme ↑substrate  ↑number of reactions Product formation Substrate conc. limiting

3. Enzyme concentration More enzyme  more chance of a collision ↑ Reaction rate Enzyme activity will not increase If enzymes are limiting, reaction rate will drop off, but enzymes are re-usable, so the reaction will continue

4. EFFECT OF ENZYME CONC. ON REACTIONS Enzyme concentration Reaction rate levels off or stops. eg substrate runs out Rate of reaction Reaction rate increases rapidly. Enzyme conc. is limiting

5. Enzyme cofactors • May be • Organic co-enzymes, usually vitamins egvit B • Activating ions eg Na+, K+, Ca2+, Mg2+ • complete or alter the enzyme active site • increase enzyme activity (enzyme molecules work more effectively) • Without the cofactors the enzyme will not work, or will work too slowly.

6. EFFECT OF COFACTOR CONC. ON REACTIONS Cofactor concentration Rate of reaction levels off. Not enough enzyme for the co-factors to attach to – enzymes are limiting Rate of reaction Rate of reaction increases rapidly. Cofactor conc. is limiting

7. Inhibitors Competitive inhibitors bind to the enzyme active site, so substrate cannot bind (eg the product of a reaction may bind, preventing too much product being formed) Non-competitive inhibitors (allosteric) usually bind somewhere other than the active site, denaturing the enzyme permanently (eg many poisons, such as heavy metal ions, act this way) Reactions stops or occurs at a very low rate

8. EFFECT OF INHIBITOR CONC. ON REACTIONS Inhibitor concentration Rate of reaction decreases rapidly. Rate of reaction

9. Temperature At low temperatures enzymes and substrates have less energy, so they move less and collide less often. However, at temperatures a little over the optimal temperature the enzymes become denatured and reaction comes to a stop. Denaturation = change in protein shape  enzyme can’t function

10. EFFECT OF TEMPERATURE ON REACTIONS Temperature Low temp. limits the rate of reaction, up to an optimal temp. Optimum ↑ temp  ↑ energy  ↑ reaction rate Denaturation – irreversible shape change - can’t function Rate of reaction

11. 3-dimensional enzyme structure Globular proteins with a very specific shape Change shape  active site changes • Cannot bind substrate • Enzyme cannot function

12. Each enzyme has its own optimal pH At pHs above or below this optimum, enzyme denatures pH Rate of reaction PEPSIN AMYLASE TRYPSIN pH 2 pH7 pH9 EFFECT OF pH ON ENZYME ACTIVITY

13. MENU Quick Quiz Key Words Videos MCQ Exercises

14. Key words Back to menu • Limiting • Reaction rate • Optimal • Substrate conc. • Enzyme conc. • Co-factor • Co-enzyme • Activating ion • Competitive inhibitor • Non-competitive inhibitor • Temperature • Denaturation • pH

15. Quick quiz Back to menu • ____ factors prevent reaction occurring at optimal rate • As substrate conc. increases, the chance of a ____ between substrate and enzyme increases • As enzyme increases, reaction rate increases until another factor becomes ____ • Enzyme ____ include co-enzymes and ions • ____, such as poisons, decrease reaction rates • 35-37oc is the ____ range of temp.s for most enzymes • Enzymes become ____ at high temperatures • Different enzymes have different ____ pH ranges • Vitamins often act as ____ • Low temperatures denature enzymes – True / False? Answers

16. Quick quiz Back to menu • Limitingfactors prevent reaction occurring at optimal rate • As substrate conc. increases, the chance of a collision between substrate and enzyme increases • As enzyme concentration increases, reaction rate increases until another factor becomes limiting • Enzyme co-factors include co-enzymes and ions • Inhibitors, such as poisons, decrease reaction rates • 35-37oc is the optimalrange of temp.s for most enzymes • Enzymes become denatured at high temperatures • Different enzymes have different optimal pH ranges • Vitamins often act as co-enzymes • Low temperatures denature enzymes – True / False?

17. Exercise Back to menu • Workbook pp50-52, qq18-20 and 22-23 • Booklet p3 • READING • Pathfinder p48 (or p42) Enzymes & reaction rate • Excellence in Biology pp114-6

18. Competitive and non-competitive inhibitors

19. Videos • http://www.youtube.com/watch?v=E90D4BmaVJM&feature=related (10 min, includes biotechnology) http://www.youtube.com/watch?v=2DRWqBld7XU&feature=related (feedback inhibition, 1 min) http://www.youtube.com/watch?v=PILzvT3spCQ&feature=related (1 min)

20. Question 1 34 Increasing substrate conc. increases rate of reaction because... (a)the activation energy decreases (b)the enzymes act as catalysts √ (c)there is more chance of a collision with enzymes (d)the enzymes are proteins

21. 35 Question 2 Increasing enzyme conc. increases the reaction rate because.... (a)enzymes form an enzyme-substrate complex (b)reactions are exergonic √ (c)there is more chance of a collision with substrate (d)enzymes are specific

22. 37 Question 3 At very high substrate concentrations, the increase in reaction rate levels off because... √ (a)enzymes become limiting (b) the substrate precipitates out (c)the enzymes become denatured (d) a combination of these

23. 38 Question 4 Co-factors (a)lower reaction rates (b)inhibit the action of enymes (c) slow down a reaction √ (d)include co-enzymes and activating ions

24. Question 5 39 Co-factors √ (a) complete or alter the active site of the enzyme (b)are always organic molecules (c) are a type of enzyme (d)can be any chemical substance in a cell

25. 40 Question 6 Inhibitors (a) combine with different substrates (b) form different kinds of end-product (c) function at temperatures above 90oC √ (d)may be competitive or non-competitive

26. 41 Question 7 Inhibitors can include (a)co-enzymes √ (b) poisons (c) co-factors (d) activating ions

27. Question 8 42 After being exposed to a high temperature an enzyme cannot function because..... (a) it has been broken down √ (b) its shape has been changed (c) its composition has been changed (d) it cannot separate from its substrate

28. ANSWER 43 Back to menu Correct √ click arrow to return

29. 44 ANSWER Back to menu IncorrectX click arrow to return