Limiting factors Factors affecting the rate of reactions

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

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

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

Enzyme cofactors May be –Organic co-enzymes, usually vitamins eg vit B –Activating ions eg Na +, K +, Ca 2+, Mg 2+ 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.

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

Inhibitors Competitive 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 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

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

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

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

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

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

MENU Key Words Exercises Quick Quiz MCQ Videos

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

Quick quiz 1.____ factors prevent reaction occurring at optimal rate 2.As substrate conc. increases, the chance of a ____ between substrate and enzyme increases 3.As enzyme increases, reaction rate increases until another factor becomes ____ 4.Enzyme ____ include co-enzymes and ions 5.____, such as poisons, decrease reaction rates o c is the ____ range of temp.s for most enzymes 7.Enzymes become ____ at high temperatures 8.Different enzymes have different ____ pH ranges 9.Vitamins often act as ____ 10.Low temperatures denature enzymes – True / False? Back to menu Answers

Quick quiz 1.Limiting factors prevent reaction occurring at optimal rate 2.As substrate conc. increases, the chance of a collision between substrate and enzyme increases 3.As enzyme concentration increases, reaction rate increases until another factor becomes limiting 4.Enzyme co-factors include co-enzymes and ions 5.Inhibitors, such as poisons, decrease reaction rates o c is the optimal range of temp.s for most enzymes 7.Enzymes become denatured at high temperatures 8.Different enzymes have different optimal pH ranges 9.Vitamins often act as co-enzymes 10.Low temperatures denature enzymes – True / False? Back to menu

Exercise Workbook pp50-52, qq18-20 and Booklet p3 Back to menuREADING Pathfinder p48 (or p42) Enzymes & reaction rate Excellence in Biology pp114-6

Competitive and non- competitive inhibitors

Videos M&feature=related (10 min, includes biotechnology) M&feature=related ature=related ature=related (feedback inhibition, 1 min) ture=relatedhttp:// ture=related (1 min)

Question 1 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 34 √

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

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 37 √

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 38 √

Question 5 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 39 √

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

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

Question 8 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 42 √

ANSWER Correct √ 43 click arrow to return Back to menu

ANSWER Incorrect X 44 click arrow to return Back to menu