1. Chapter 7 Lecture Outline
Energy and Enzymes

2. Energy in Living Systems
Metabolism is the sum of all chemical reactions in the body.
Metabolism transfers energy and follows the laws of thermodynamics.
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3. Laws of Thermodynamics
1st Law: Energy cannot be either created or destroyed
2nd Law: When reactions occur, they become more disordered
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4. The Carbon Cycle and Energy
Living organisms all require energy to survive
Sun is source of most energy on Earth
Light energy is used by producers to synthesize sugars
Plants performing photosynthesis
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6. The Carbon Cycle and Energy
For non-photosynthesizing organisms (mostly consumers), energy is acquired from food molecules.
Carbon dioxide and food molecules are involved in this energy transfer.
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The Carbon Cycle
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Using Energy from Food
Energy transfer in nonliving systems can be explosive:
Carbon in wood + O2  CO H2O + energy
Energy transfer in cells must be controlled:
Carbon in food + O2  CO2 + H2O + energy
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Transfer of Electrons
Capturing energy requires transfer of electrons
Reactions that transfer electrons are called redox (oxidation/reduction) reactions
Oxidation—loss of electrons
Reduction—gain of electrons
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Metabolism
All chemical reactions within living cells
Anabolic
Biosynthetic: create complex molecules out of smaller compounds
Catabolic
Break down complex molecules to release energy
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14. Chemical reactions and thermodynamics
A + B  C + D
Reactants: A + B
Products: C + D
Some chemical reactions need a “jump start” to proceed
Activation energy:
Energy needed to jump‑start a reaction
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16. Enzymes Speed Up Reactions
Enzymes are biological catalysts
Lower the energy of activation
Increase the speed of reaction
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18. The Structure of Enzymes
Very specific for reactions
Three‑dimensional shape determines function
Active site is region where the substrate binds
Induced fit: active site molds around substrate
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19. Enzymes as Molecular Matchmakers
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Enzymes in Metabolism
Metabolic pathways in the body usually involve several reactions.
There may be several intermediates.
Each intermediate has its own enzyme. B A C D
Enzyme 1
Enzyme 2
Enzyme 3
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Enzyme Function
Enzymes depend on random collisions.
Multiple enzymes may be located close together.
This maximizes molecular collisions.
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23. Metabolism and Life Span
Slowing down metabolism increases life span
Higher metabolism results in toxic by products (free radicals)
Antioxidants help break down free radicals
Some examples of antioxidants
Vitamin E
Vitamin C
Beta-carotene
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Concept Quiz
Why are high fevers dangerous and
sometimes life‑threatening?
Molecules move faster at higher temperatures.
Enzymes may change shape at high temperatures.
Invading microbes survive better and reproduce faster at high temperatures.
The correct answer is B. High fevers are life-threatening for a long period of time because enzymes begin to denature at higher temperatures.
Lower fevers can actually be beneficial to the body. It is the natural defense mechanism.
Molecules do move faster at higher temperatures, but this answer choice does not address the question.
Microbes may reproduce faster at higher temperatures, up to an optimal temperature. Higher than the optimum, microbes can be destroyed.
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Concept Quiz
The loss of electrons is called
Oxidation
Reduction
Redox
The correct answer is A.
Students often incorrectly think of loss of electrons as reduction.
Remind them if something is being reduced, it is acquiring a negative charge and, therefore, gaining an electron.
Redox refers to both oxidation and reduction.
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Concept Quiz
Where a substrate binds to an enzyme is known as the
Active site
Activation energy
Energy transfer site
The correct answer is A. The active site is where a substrate binds. The shape of the active site dictates the enzyme’s activity and which substrates may bind to it.
Activation energy is the energy required to start a reaction.
Energy transfer site is listed as a distraction.
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Biology in the News
Doctors Warned about Common Drugs for Pain; NSAIDs Tied to Risk of Heart Attack, Stroke
NSAIDs: Non‑steroid anti‑inflammatory drugs
Two major categories
COX-1 inhibitors
May result in stomach problems
COX-2 inhibitors
Long-term use associated with heart disease
Removed from the market
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Terms
Activation energy
Active site
Anabolic reaction
Biosynthetic reaction
Catabolic reaction
Catalyst
Coupled reaction
Enzyme
First law of thermodynamics
Induced fit model
Kinetic energy
Metabolic pathway
Metabolism
Oxidation
Potential energy
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Terms
Products
Redox reaction
Reactants
Reduction
Second law of thermodynamics
Substrate
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Process Animation 7.1a The Energy of Chemical Reactions
Macintosh
Windows
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Process Animation 7.1b Heat and Chemical Reactions
Macintosh
Windows
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Process Animation 7.1c Enzyme Catalysis
Macintosh
Windows
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35. © 2009 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 4/e
Process Animation 7.1d Enzymes and Activation Energy
Macintosh
Windows
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36. Discover Biology StudySpace

37. Additional Art from Chapter 7
All art files from the book are available in JPEG and PPT formats on the Instructor Resource Disc

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