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Please Take out the Following. Pencil Science Journal Agendas Macromolecules Worksheet (Pass it forward if you have not done so already). Plan for the week. Science Question of the Day. - PowerPoint PPT PresentationTRANSCRIPT
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Please Take out the Following
PencilScience JournalAgendasMacromolecules Worksheet (Pass it forward if you have not done so already).Plan for the week
Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Science Question of the Day
Explain why the chemical bonds in the body do not break down, spontaneously, releasing all of their energy.
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5.3 Chemical Reactions
Chemical reactions begin with reactants (substrates) which are converted to products
Exergonic reactionsProducts contain less energy than the reactants
Endergonic reactionsProducts contain more energy than the reactants
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Energy of ActivationExtra energy required to destabilize chemical bonds and so initiate a chemical reaction
Fig. 5.4
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Catalysts lower the activation energy of a reaction, and thus increase its rate
However, they cannot make an endergonic reaction exergonic
Fig. 5.4
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5.4 How Enzymes Work
Enzymes are proteins that serve as catalystsThey speed up chemical reactions within cells
Enzymes bind a specific molecule and stress bonds to make a particular reaction more likely
Active siteSite on enzyme surface where reactant fits
Binding siteSite on reactant where enzyme binds
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Fig. 5.5 Enzyme shapes determines its activity
Lysozyme
Changes upon binding of the
substrateThe substrate is now bound more
intimately
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Fig. 5.6 How enzymes work
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Fig. 5.7 The catalytic cycle of an enzyme
1 The substrate, sucrose, consistsof glucose and fructose bonded together.
Bond
Enzyme
Active site
The substrate binds to the enzyme, forming an enzyme-substrate complex.
2
H2O
The binding of the substrate and enzyme places stress on the glucose-fructose bond, and the bond breaks.
3
Glucose Fructose
Products are released, and the enzyme is free to bind other substrates.
4
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5.5 Factors Affecting Enzyme Activity
Enzyme activity is affected by any change in condition that alters the enzyme’s 3-D shape
The structural bonds of enzymes are sensitive to changes in temperature and pH
Therefore, a temperature or pH beyond the optimal range will cause the enzyme to denature
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Enzyme Activity
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Fig. 5.8 Enzymes are sensitive to their environment
Digests proteins in
the intestine
Digests proteins in
the stomach
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5.6 How Cells Regulate Enzymes
A cell can control the activity of an enzyme by altering its shape
Allosteric enzymes have shapes that can be altered by the binding of signal molecules
These molecules bind to the allosteric site
Repressors bind and repress enzyme activity
Activators bind and restore or increase enzyme activity
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Fig. 5.9 How cells control enzymes
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Enzyme inhibition occurs in two ways:Competitive inhibition- Inhibitor binds at the
enzyme’s active site
Noncompetitive inhibition- Inhibitor binds at the
enzyme’s allosteric site
Fig. 5.10
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Enzymes Reviewed