Optimum Substrate

ProteinUnchanged

Temperature

Specific

Product

pH

Active siteCatalyst

Chemical reactions in a living cell

Metabolic reactions

Normally too slow to sustain life.

SUBSTRATE(S) reaction PRODUCT(S)

Catalysts speed up reactions

Catabolic reactions break down molecules eg digestion

Metabolism

Anabolic reactions build up molecules eg photosynthesis

Enzymes are proteins which act as biological catalysts – they speed up biological reactions which otherwise would be too slow to sustain life

Enzymes

Enzymes are usually Specific for a substrate or group of substrates (the chemicals they act on)

Enzymes are unchanged by reaction

Summary

Enzyme-substrate complex

ENZYME

SUBSTRATE

PRODUCT

Enzyme brings reactive parts of substrates together for reaction to

occur

Enzyme-substrate complex

ENZYME

SUBSTRATE

PRODUCT

Enzyme brings reactive parts of substrate together for reaction to

occur

Summary

Enzyme will only bind substrates that fit exactly into the active site

Lock and Key model

SUBSTRATE

enzyme

Enzyme-SUBSTRATE complex

products

http://www.youtube.com/watch?v=CZD5xsOKres&feature=related

Induced fit model

Substrate causes shape change in active site

SUBSTRATE

Enzyme-SUBSTRATE complex

products

http://www.5min.com/Video/Enzyme-Action-The-Induced-Fit-Model-150616169 (12 min)

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• Certain conditions permanently break

bonds that hold the enzyme’s 3D shape.

• Active site shape destroyed

enzyme high temperaturecannot function

Summary

Activation EnergyReactions 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

A

B

Activation Energy

A

B

Enzymes lower the activation energy required to start a reaction

Summary

http://www.youtube.com/watch?v=VbIaK6PLrRM&feature=related (1 min)

MENU

Key Words

Exercises

Quick Quiz

MCQ

VideosRecapExtra slides

Key words• Metabolism• Substrate• Product• Reaction rate• Enzyme• Globular protein• Biological catalyst• 3D structure• Denaturation• Active site• Specificity

• Enzyme-substrate complex

• Lock and Key model• Induced fit model• Exergonic• Endergonic• Activation energy

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Quick quiz1. Chemical reactions in living cells are _____ reactions

2. ____ reactions build up molecules

3. ____ reactions break down molecules

4. ____ speed up reactions

5. ____ are biological catalysts

6. Enzymes are made of ____

7. Enzymes are ____-shaped

8. Enzyme function depends on its ____

9. The ____ site of the enzyme binds with the substrate

10.____ model: substrate must fit exactly into the enzyme

11.____ model: enzyme shape can change to fit

12.Enzymes lower the ____ required to initiate a reaction

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Answers

Quick quiz1. Chemical reactions in living cells are metabolic

reactions

2. Anabolic reactions build up molecules

3. Catabolic reactions break down molecules

4. Catalysts speed up reactions

5. Enzymes are biological catalysts

6. Enzymes are made of protein

7. Enzymes are globular-shaped

8. Enzyme function depends on its shape

9. The active site of the enzyme binds with the substrate

10.Lock and key model: substrate must fit exactly into the enzyme

11.Induced fit model: enzyme shape can change to fit

12. Enzymes lower the activation energy required to initiate a reaction

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Exercise• 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

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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

(b) changing their chemical composition

(c) changing their shape

(d) making them soluble

34

√

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Question 2

A protein is made up of a series of

(a) glucose units

(b) fatty acids

(c) amino acids

(d) carbohydrates

35

√

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Question 3

Enzymes are

(a) proteins

(b) lipids

(c) carbohydrates

(d) a combination of these

37

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Question 4

An enzyme can

(a) change a reaction

(b) prevent a reaction

(c) slow down a reaction

(d) speed up a reaction

38

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Question 5

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

39

√

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Question 6

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

40

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Question 7

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

41

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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

√

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ANSWER

Correct

√

43

click arrow to return

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ANSWER

IncorrectX

44

click arrow to return

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Oooops!

RECAP Back to Menu

Your choice

Copy diagrams from Workbook p50 or Pathfinder p42

Highlight key ideas in your

workbook

Add key words and definitions to

your glossary

Summarise the notes on enzymes from

workbook & pathfinder

Past Papers 2006-2009 Q2

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

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SUBSTRATE

enzyme

Enzyme-SUBSTRATE complex

enzyme

products

Lock and Key Model Back to Menu

SUBSTRATE

enzyme

Enzyme-SUBSTRATE complex

enzyme

products

Induced Fit Model Back to Menu

Exergonic reactions

Substrates have more energy than the products

eg respiration breaks down sugar to release energy

ENERGY

REACTION

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Endergonic reactions

Substrates have less energy than the products

ENERGY

REACTION

eg photosynthesis uses solar energy to make sugar

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Activation energy

Nett energy released by

reactionFre

e en

ergy

Time

Activation energy

Nett energy used by reactionF

ree

ener

gy

Time

Exergonic

Energy released by reaction

Endergonic

Energy used by reactionBack to Menu

The end……………………….

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