optimumsubstrate protein unchanged temperature specific product ph active site catalyst
TRANSCRIPT
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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