Enzymes Optimum Substrate Product Temperature Specific pH Unchanged Protein ACTIVITY: How many sentences about enzymes can you make using these words? Catalyst Active site

Metabolic reactions Normally too slow to sustain life. Chemical reactions in a living cell PRODUCT(S) SUBSTRATE(S) reaction Normally too slow to sustain life. Catalysts speed up reactions

Metabolism Catabolic reactions break down molecules eg digestion Anabolic reactions build up molecules eg photosynthesis

Enzymes are unchanged by reaction Enzymes are proteins which act as biological catalysts – they speed up biological reactions which otherwise would be too slow to sustain life Enzymes are unchanged by reaction Enzymes are usually Specific for a substrate or group of substrates (the chemicals they act on) Summary

Enzyme-substrate complex Enzyme brings reactive parts of substrates together for reaction to occur ENZYME PRODUCT

Enzyme-substrate complex Enzyme brings reactive parts of substrate together for reaction to occur Enzyme-substrate complex Summary ENZYME PRODUCT

Lock and Key model SUBSTRATE products enzyme Does not fully explain the functioning of all enzymes Enzyme-SUBSTRATE complex http://www.youtube.com/watch?v=CZD5xsOKres&feature=related Enzyme will only bind substrates that fit exactly into the active site

Induced fit model Substrate causes shape change in active site products http://www.5min.com/Video/Enzyme-Action-The-Induced-Fit-Model-150616169 (12 min) Enzyme-SUBSTRATE complex Substrate causes shape change in active site

Theories of enzyme action COMPARE: In both models an enzyme-substrate complex is formed the activation energy is lowered enzyme remains unchanged afterwards substrate  products CONTRAST: In lock and key model substrate must fit active site exactly in order to bind, whereas with the induced fit model the substrate can cause active site to change slightly to allow a fit. Summary

Denaturing proteins Summary Certain conditions permanently break bonds that hold the enzyme’s 3D shape. Active site shape destroyed enzyme high temperature cannot function Summary

Activation Energy A B Reactions require energy to get them going To get the ball to B, you need to give it enough energy to get over the top – even though B is lower than A B

Activation Energy Summary A B Enzymes lower the activation energy required to start a reaction http://www.youtube.com/watch?v=VbIaK6PLrRM&feature=related (1 min) A Summary B

MENU Quick Quiz Key Words Exercises MCQ Recap Videos Extra slides

Key words Metabolism Enzyme-substrate complex Substrate Back to menu Metabolism Enzyme-substrate complex Substrate Lock and Key model Product Induced fit model Reaction rate Exergonic Enzyme Endergonic Globular protein Activation energy Biological catalyst 3D structure Denaturation Active site Specificity

Quick quiz Chemical reactions in living cells are _____ reactions Back to menu Chemical reactions in living cells are _____ reactions ____ reactions build up molecules ____ reactions break down molecules ____ speed up reactions ____ are biological catalysts Enzymes are made of ____ Enzymes are ____-shaped Enzyme function depends on its ____ The ____ site of the enzyme binds with the substrate ____ model: substrate must fit exactly into the enzyme ____ model: enzyme shape can change to fit Enzymes lower the ____ required to initiate a reaction Answers

Quick quiz Chemical reactions in living cells are metabolic reactions Back to menu Chemical reactions in living cells are metabolic reactions Anabolic reactions build up molecules Catabolic reactions break down molecules Catalysts speed up reactions Enzymes are biological catalysts Enzymes are made of protein Enzymes are globular-shaped Enzyme function depends on its shape The active site of the enzyme binds with the substrate Lock and key model: substrate must fit exactly into the enzyme Induced fit model: enzyme shape can change to fit Enzymes lower the activation energy required to initiate a reaction

Exercise Workbook pp 50-1, qq15-17 Pathfinder pp44-5 (or 50-51) qq 3-6 Back to menu Workbook pp 50-1, qq15-17 Pathfinder pp44-5 (or 50-51) qq 3-6 EXTRA READING Pathfinder p48 (or p42) Proteins and Enzymes Excellence in Biology p114-116 Booklet p3

Videos Back to menu http://www.youtube.com/watch?v=E90D4BmaVJM&feature=related (10 min, includes biotechnology) http://www.youtube.com/watch?v=MUtfF2qnzGo&feature=related (metabolism1, 6 min) http://www.youtube.com/watch?v=AEsQxzeAry8&feature=related (digestion by enzymes, 3min)

√ Question 1 High temperatures damage proteins by (a) decomposing them 34 Back to menu High temperatures damage proteins by (a) decomposing them (b) changing their chemical composition √ (c) changing their shape (d) making them soluble

√ Question 2 A protein is made up of a series of (a) glucose units 35 Back to menu A protein is made up of a series of (a) glucose units (b) fatty acids √ (c) amino acids (d) carbohydrates

√ Question 3 Enzymes are (a) proteins (b) lipids (c) carbohydrates 37 Back to menu Enzymes are √ (a) proteins (b) lipids (c) carbohydrates (d) a combination of these

√ Question 4 An enzyme can (a) change a reaction 38 Back to menu An enzyme can (a) change a reaction (b) prevent a reaction (c) slow down a reaction √ (d) speed up a reaction

√ Question 5 A substrate is a substance which (a) an enzyme acts on 39 Back to menu A substrate is a substance which √ (a) an enzyme acts on (b) is produced by an enzyme reaction (c) is a particular kind of enzyme (d) is any chemical substance in a cell

√ Question 6 An enzyme can (a) combine with different substrates 40 Back to menu An enzyme can (a) combine with different substrates (b) form different kinds of end-product (c) function at temperatures above 90oC √ (d) lower the activation energy needed for a reaction

Question 7 41 Back to menu The part of an enzyme which combines with the substrate is called: (a) the reaction centre √ (b) the active site (c) the action centre (d) the reaction site

Question 8 42 Back to menu 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

ANSWER 43 Back to menu Correct √ click arrow to return

ANSWER 44 Back to menu IncorrectX click arrow to return Oooops!

RECAP Back to Menu Your choice Past Papers 2006-2009 Q2 Highlight key ideas in your workbook Copy diagrams from Workbook p50 or Pathfinder p42 Summarise the notes on enzymes from workbook & pathfinder Add key words and definitions to your glossary

3-dimensional enzyme structure Globular proteins – long polypeptides held in shape by various bonds between side groups (eg hydrogen and ionic bonds) to form globules (ball-shaped) Polypeptide = chain of amino acids Polypeptide = chain of amino acids Back to Menu

Lock and Key Model Back to Menu products SUBSTRATE enzyme Enzyme-SUBSTRATE complex products Lock and Key Model

Induced Fit Model Back to Menu SUBSTRATE products enzyme Enzyme-SUBSTRATE complex products Induced Fit Model

Exergonic reactions Substrates have more energy than the products Back to Menu Substrates have more energy than the products ENERGY REACTION eg respiration breaks down sugar to release energy

Endergonic reactions Substrates have less energy than the products Back to Menu Substrates have less energy than the products ENERGY REACTION eg photosynthesis uses solar energy to make sugar

Exergonic Energy released by reaction Endergonic Energy used by reaction Back to Menu Activation energy Nett energy released by reaction Free energy  Time  Activation energy Nett energy used by reaction Free energy  Time 

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