1. Overview: The Energy of Life
The living cell is a miniature chemical factory where thousands of reactions occur
The cell takes energy from food or light, converts it into different forms, and uses that energy to do work (like active transport, contracting muscles, and keeping you warm)
Remember, energy = the capacity to cause change
A reaction = making and breaking bonds
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2. Animation: Energy Concepts
Kinetic energy is energy associated with motion
Potential energy is energy that matter possesses because of its location or structure
Other types of energy can be either potential or kinetic
Animation: Energy Concepts
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

3. Fig. 8-2
A diver has more potential
energy on the platform
than in the water.
Diving converts
potential energy to
kinetic energy.
Figure 8.2 Transformations between potential and kinetic energy
Climbing up converts the kinetic
energy of muscle movement
to potential energy.
A diver has less potential
energy in the water
than on the platform.

4. Radiant energy
Thermal energy (heat) is kinetic energy associated with random movement of atoms or molecules
Chemical energy is potential energy available for release in a chemical reaction
Light energy is kinetic energy from the movement of electromagnetic waves that form light
Figure 8.1 What causes the bioluminescence in these fungi?
Heat (thermal energy) is kinetic energy associated with random movement of atoms or molecules
Chemical energy is potential energy available for release in a chemical reaction
Radiant energy is kinetic energy from the movement of electromagnetic waves that form light

5. The Laws of Energy Transformation
A system is a group of parts that work together
Cells, communities, organisms and populations are all systems
A system is open if it exchanges matter and/or energy with its environment
A system is closed if it doesn’t exchange anything with its environment
Thermodynamics is the study of energy transformations. Open systems take in energy from other sources (like food) and transform it into other kinds of energy (like ATP)
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6. The First Law of Thermodynamics
According to the first law of thermodynamics, the energy of the universe is constant:
– Energy can be transferred and transformed, but it cannot be created or destroyed
The first law is also called the principle of conservation of energy
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7. The Second Law of Thermodynamics
During every energy transfer or transformation, some energy is unusable, and is often lost as heat
According to the second law of thermodynamics:
– Every energy transfer or transformation increases the entropy (disorder or chaos) of the universe
Heat (thermal energy) is the most disordered and random form of energy.
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8. Living cells unavoidably convert organized forms of energy to heat
Fig. 8-3
Living cells unavoidably convert organized forms of energy to heat
Heat
CO2 +
Chemical
energy
H2O
Figure 8.3 The two laws of thermodynamics
(a) First law of thermodynamics
(b) Second law of thermodynamics

9. If the 2nd law of thermodynamics says that entropy increases every time energy is transferred, how can simple systems like a single egg cell develop into complex organisms?

10. Organisms are open systems; we’re constantly exchanging energy with our environments. We can take in ordered forms of energy and send our disordered forms of energy off somewhere else in the universe.

11. Living cells unavoidably convert organized forms of energy to heat whenever they perform chemical reactions
Metabolism is the name for an organism’s total chemical reactions that it does to sustain life
Includes things like burning calories to make ATP, active transport (which allows things like nerve cell communication), muscle contractions, building proteins and organelles for new cells, etc.
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12. Organization of the Chemistry of Life into Metabolic Pathways
A metabolic pathway is a series of chemical reactions that change a starting reactant into an end product.
Each step is catalyzed by a specific enzyme
Without enzymes, metabolic pathways would be too slow to sustain life
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13. Starting molecule Product
Fig. 8-UN1
Enzyme 1
Enzyme 2
Enzyme 3 A B C D
Reaction 1
Reaction 2
Reaction 3
Starting
molecule
Product

14. 2 Main Kinds of Pathways : Catabolic
Catabolic pathways and reactions release energy by breaking down complex molecules into simpler compounds
Cellular respiration, the breakdown of glucose in the presence of oxygen to make ATP, is an example of a catabolic pathway
Catabolic pathways are also called spontaneous reactions because they can happen on their own (they don’t require a big input of energy).
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15. Cats break things. Catabolic pathways break larger molecules down into smaller molecules.

16. 2 Main Kinds of Pathways : Anabolic
Anabolic pathways consume (use up) energy to build complex molecules out of simpler ones
The synthesis of a protein from amino acids is an example of an anabolic reaction.
Anabolic pathways are non-spontaneous because they require energy; they don’t just happen automatically.
Would dehydration reactions be catabolic or anabolic? What about hydrolysis?
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17. The free-energy change of a reaction tells us whether or not the reaction occurs spontaneously
Biologists want to know which reactions occur spontaneously (catabolic) and which require energy inputs (anabolic)
To do so, they need to determine energy changes that occur in chemical reactions
How much energy did the reactants start with? Did they gain more as the reaction progressed? Or did they end up with less energy at the end?
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18. Free-Energy Change, G
A living system’s free energy (G) is energy that is available to do work
It’s not locked up inside a molecule and unavailable for use in the reaction.
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19. G(products) – G(reactants) = ∆G
The change in free energy (∆G) during a process is equal to the free energy of the products minus the free energy of the reactants.
G(products) – G(reactants) = ∆G
The amount of energy we ended up with minus what we started with.
Enthalpy = capacity to do non-mechanical work + capacity to release heat
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20. Free Energy, Stability, and Equilibrium
Free energy is a measure of a system’s instability, its tendency to change to a more stable state
During a spontaneous change, free energy decreases and the stability of a system increases
Equilibrium is a state of maximum stability
At equilibrium, ∆G = 0 and no more work can be done.
For the purposes of biological organisms,
equilibrium = death.
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21. (a) Gravitational motion (b) Diffusion (c) Chemical reaction
Fig. 8-5b
Spontaneous
change
Spontaneous
change
Spontaneous
change
Figure 8.5 The relationship of free energy to stability, work capacity, and spontaneous change
(a) Gravitational motion
(b) Diffusion
(c) Chemical reaction

22. Exergonic and Endergonic Reactions in Metabolism
An exergonic reaction proceeds with a net release of free energy and is spontaneous
These are catabolic
An endergonic reaction absorbs free energy from its surroundings and is nonspontaneous
These are anabolic
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23. Amount of energy released (∆G < 0)
Fig. 8-6a
Reactants
Amount of
energy
released
(∆G < 0)
Free energy
Energy
Products
Figure 8.6a Free energy changes (ΔG) in exergonic and endergonic reactions
Progress of the reaction
(a) Exergonic reaction: energy released

24. Amount of energy required (∆G > 0)
Fig. 8-6b
Products
Amount of
energy
required
(∆G > 0)
Energy
Free energy
Reactants
Figure 8.6b Free energy changes (ΔG) in exergonic and endergonic reactions
Progress of the reaction
(b) Endergonic reaction: energy required

25. Equilibrium and Metabolism
Reactions in a closed system eventually reach equilibrium and then do no work
Cells are not in equilibrium; they are open systems that are constantly exchanging energy and matter with their environments
A defining feature of life is that metabolism is never at equilibrium
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26. (a) An isolated hydroelectric system
Fig. 8-7a
∆G < 0
∆G = 0
Figure 8.7a Equilibrium and work in isolated and open systems
(a) An isolated hydroelectric system

27. (b) An open hydroelectric system
Fig. 8-7b
∆G < 0
Figure 8.7b Equilibrium and work in isolated and open systems
(b) An open hydroelectric system

28. (c) A multistep open hydroelectric system
Fig. 8-7c
∆G < 0
∆G < 0
∆G < 0
Figure 8.7c Equilibrium and work in isolated and open systems
(c) A multistep open hydroelectric system

29. ATP powers cellular work by coupling exergonic reactions to endergonic reactions
To do work, cells manage energy resources by energy coupling, the use of an exergonic (catabolic) process to drive an endergonic (anabolic) one
In cells, ATP provides the exergonic process that powers most of your endergonic reactions.
ATP breaks down, providing power for anabolic reactions
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30. Energy Coupling AB  A + B + energy Energy + C + D  CD
Exergonic reaction releases energy (ATP breaking down)
AB  A + B + energy
Energy + C + D  CD
Energy released from the exergonic reaction is used to power an endergonic reaction

31. What kind of molecule does ATP look like?
ATP (adenosine triphosphate) is the cell’s energy shuttle and is composed of ribose (a sugar), adenine (a nitrogenous base), and three phosphate groups
Phosphate groups
Ribose
Adenine
For the Cell Biology Video Space Filling Model of ATP (Adenosine Triphosphate), go to Animation and Video Files.
What kind of molecule does ATP look like?
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

32. Energy is released from ATP when the end phosphate bond is broken
The bonds between the phosphate groups of ATP’s tail can be broken by hydrolysis
Energy is released from ATP when the end phosphate bond is broken
ATP  ADP + Pi + energy
For the Cell Biology Video Stick Model of ATP (Adenosine Triphosphate), go to Animation and Video Files.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

33. H2O P P P Adenosine triphosphate (ATP) P + P P + Energy
Fig. 8-9 P P P
Adenosine triphosphate (ATP)
H2O
Figure 8.9 The hydrolysis of ATP P + P P +
Energy i
Inorganic phosphate
Adenosine diphosphate (ADP)

34. How ATP Does Work
The three types of cellular work (mechanical, transport, and chemical) are powered by the hydrolysis of ATP
In the cell, the energy from the exergonic reaction of ATP hydrolysis can be used to drive an endergonic reaction
Overall, the coupled reactions are exergonic
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35. Energy Coupling with ATP
Exergonic reaction of ATP releases energy ATP + H2O ADP + Pi + energy energy + molecule + other molecule  bigger molecule Endergonic reaction gets the energy it needs from the exergonic reaction (ATP hydrolysis)

36. The sodium potassium pump gets phosphorylated
ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant
The molecule that received the phosphate group is now phosphorylated
Na+
Na+
The sodium potassium pump gets phosphorylated
Na+
ATP P
ADP
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37. ∆G = +3.4 kcal/mol Glutamic acid Ammonia Glutamine
Fig. 8-10
NH2
NH3 +
∆G = +3.4 kcal/mol
Glu
Glu
Glutamic
acid
Ammonia
Glutamine
(a) Endergonic reaction 1
ATP phosphorylates
glutamic acid,
making the amino
acid less stable. P +
ATP +
ADP
Glu
Glu
NH2 P 2
Ammonia displaces
the phosphate group,
forming glutamine.
NH3 + + P i
Glu
Glu
Figure 8.10 How ATP drives chemical work: Energy coupling using ATP hydrolysis
(b) Coupled with ATP hydrolysis, an exergonic reaction
(c) Overall free-energy change

38. Membrane protein Solute Solute transported Vesicle Cytoskeletal track
Fig. 8-11
Membrane protein P P i
Solute
Solute transported
(a) Transport work: ATP phosphorylates
transport proteins
ADP
ATP + P i
Vesicle
Cytoskeletal track
Figure 8.11 How ATP drives transport and mechanical work
ATP
Motor protein
Protein moved
(b) Mechanical work: ATP binds noncovalently
to motor proteins, then is hydrolyzed

39. The Regeneration of ATP
ATP is a renewable resource that is regenerated by adding a phosphate group to adenosine diphosphate (ADP)
Is adding a phosphate group to ADP catabolic or anabolic?
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40. Fig. 8-12
ATP +
H2O
Energy from
catabolism (exergonic,
energy-releasing
processes)
Energy for cellular
work (endergonic,
energy-consuming
processes)
ADP + P i
The energy to phosphorylate ADP comes from catabolic reactions in the cell (specifically, from breaking down food molecules in cellular respiration)
The chemical potential energy temporarily stored in ATP drives most cellular work
Figure 8.12 The ATP cycle

41. Enzymes speed up metabolic reactions by lowering energy barriers
A catalyst is a chemical that speeds up a reaction without being changed or destroyed by the reaction
An enzyme is a biological catalyst. Enzymes are proteins.
Each type of enzyme is specialized to speed up one particular kind of reaction. You have thousands of different kinds of enzymes, each of which speeds up one of the thousands of different kinds of reactions that happen in your body each day.
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42. Sucrose (C12H22O11) Sucrase Glucose (C6H12O6) Fructose (C6H12O6)
Fig. 8-13
The reactant (sucrose)
Sucrose (C12H22O11)
An enzyme that speeds up the digestion of sucrose
Sucrase
Figure 8.13 Example of an enzyme-catalyzed reaction: hydrolysis of sucrose by sucrase
The products (glucose and fructose)
Glucose (C6H12O6)
Fructose (C6H12O6)

43. Video link. http://highered. mcgraw-hill

44. The Activation Energy Barrier
Every chemical reaction between molecules involves bond breaking and bond forming
The initial energy needed to start a chemical reaction is called the free energy of activation, or activation energy (EA)
Activation energy is often supplied in the form of heat from the surroundings
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45. Progress of the reaction
Fig. 8-14 A B C D
Transition state A B EA C D
Free energy
Reactants A B
Figure 8.14 Energy profile of an exergonic reaction
∆G < O C D
Products
Progress of the reaction

46. How Enzymes Lower the EA Barrier
Enzymes catalyze reactions by lowering the EA barrier
Enzymes do not affect the change in free energy (∆G); instead, they hasten reactions that would occur eventually
Animation: How Enzymes Work
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47. Progress of the reaction
Fig. 8-15
Course of
reaction
without
enzyme EA
without
enzyme
EA with
enzyme
is lower
Reactants
Free energy
Course of
reaction
with enzyme
∆G is unaffected
by enzyme
Figure 8.15 The effect of an enzyme on activation energy
Products
Progress of the reaction

48. Substrate Specificity of Enzymes
The reactant that an enzyme acts on is called the enzyme’s substrate
The active site is the region on the enzyme where the substrate binds
For the Cell Biology Video Closure of Hexokinase via Induced Fit, go to Animation and Video Files.
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49. Substrate Active site Enzyme Enzyme-substrate complex (a) (b)
Fig. 8-16
Substrate
Active site
Figure 8.16 Induced fit between an enzyme and its substrate
Enzyme
Enzyme-substrate
complex
(a)
(b)

50. Catalysis in the Enzyme’s Active Site
In an enzymatic reaction, the substrate binds to the active site of the enzyme
The active site can lower an EA barrier by
Orienting substrates correctly
Straining substrate bonds
Providing a favorable microenvironment (such as a slightly different pH or charge than the surroundings)
Covalently bonding to the substrate
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51. Fig. 8-17
Substrates enter active site; enzyme
changes shape such that its active site
enfolds the substrates (induced fit). 1
Substrates held in
active site by weak
interactions, such as
hydrogen bonds and
ionic bonds. 2
Substrates
Enzyme-substrate
complex
Active site can lower EA
and speed up a reaction. 3
Active
site is
available
for two new
substrate
molecules. 6
Figure 8.17 The active site and catalytic cycle of an enzyme
Enzyme 5
Products are
released.
Substrates are
converted to
products. 4
Products

52. Effects of Local Conditions on Enzyme Activity
Remember, enzymes are proteins, and proteins can denature.
An enzyme’s activity can be affected by
General environmental factors, such as temperature and pH
Chemicals called inhibitors that specifically influence the enzyme
Inhibitors can be things like drugs, antibiotics, or even poisons
Your body makes some natural inhibitors to turn off enzymes when they are unneeded
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53. Effects of Temperature and pH
Each enzyme has an optimal temperature in which it can function
Each enzyme has an optimal pH in which it can function
Usually, enzymes are adapted to the environment where they function
For example, stomach enzymes have a very low optimum pH, as they function in the human stomach, which is very acidic
Enzymes in bacteria that live in hot springs have high optimum temperatures, because they function in bacteria that live in hot places. Bacteria with enzymes that worked well in their environments would have been more likely to survive long enough to reproduce in the past.
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54. Optimal temperature for typical human enzyme Optimal temperature for
Fig. 8-18
Optimal temperature for
typical human enzyme
Optimal temperature for
enzyme of thermophilic
(heat-tolerant)
bacteria
Rate of reaction 20 40 60 80
100
Temperature (ºC)
(a) Optimal temperature for two enzymes
Optimal pH for pepsin
(stomach enzyme)
Optimal pH
for trypsin
(intestinal
enzyme)
Figure 8.18 Environmental factors affecting enzyme activity
Rate of reaction 1 2 3 4 5 6 7 8 9 10 pH
(b) Optimal pH for two enzymes

55. Enzyme Inhibitors
Competitive inhibitors bind to the active site of an enzyme, competing with the substrate
Noncompetitive inhibitors bind to another part of an enzyme, causing the enzyme to change shape and making the active site less effective
Examples of inhibitors include toxins, poisons, pesticides, and antibiotics
The body often uses inhibitors to stop enzymes from catalyzing a reaction once there is enough product.
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56. Noncompetitive inhibitor
Fig. 8-19
Substrate
Active site
Competitive
inhibitor
Enzyme
Figure 8.19 Inhibition of enzyme activity
Noncompetitive inhibitor
(a) Normal binding
(b) Competitive inhibition
(c) Noncompetitive inhibition

57. Feedback Inhibition
In feedback inhibition, the end product of a metabolic pathway doubles as an inhibitor and shuts down the pathway
Feedback inhibition prevents a cell from wasting chemical resources by synthesizing more product than is needed
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58. Fig. 8-22
Initial substrate
(threonine)
Active site
available
Threonine
in active site
Enzyme 1
(threonine
deaminase)
Isoleucine
used up by
cell
Intermediate A
Feedback
inhibition
Enzyme 2
Active site of
enzyme 1 no
longer binds
threonine;
pathway is
switched off.
Intermediate B
Enzyme 3
Intermediate C
Figure 8.22 Feedback inhibition in isoleucine synthesis
Isoleucine
binds to
allosteric
site
Enzyme 4
Intermediate D
Enzyme 5
End product
(isoleucine)