1. Chapter 06
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2. 6.1 Life and the Flow of Energy
Energy is the ability to do work or bring about change.
Cells and organisms need a constant supply of energy.
Energy allows growth, metabolism, and reproduction.
Life on Earth is dependent on solar energy.
Photosynthesis provides nutrients for the majority of other organisms.

3. Forms of Energy Energy occurs in two forms. Types of energy
Kinetic energy ….
Potential energy …
Types of energy
Chemical energy is stored …
Mechanical energy is energy of motion ….

4. Copyright © The McGraw-Hill Companies, Inc
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Solar
energy
heat
heat
heat
heat
Chemical
energy
Mechanical energy
Figure 6.1

5. Two Laws of Thermodynamics
The flow of energy in an ecosystem can be explained by two laws of thermodynamics:
Energy cannot be created or destroyed, but it can be changed from one form to another.
Law of conservation of energy
Energy cannot be changed from one form to another without a loss of usable energy. Also known as ….

6. A leaf cell photosynthesizes.
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heat
CO2
sun
H2O
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solar energy
carbohydrate synthesis
heat
carbohydrate
muscle contraction
A leaf cell photosynthesizes.
Uses but does not create solar energy to form carbohydrates
Some energy is lost as heat, none is destroyed
A moose uses cellular respiration for movement.
Energy from carbohydrates used to power muscles

7. Two Laws of Thermodynamics
Heat released from cellular respiration or photosynthesis dissipates into the environment.
Heat energy is not useful – it is not available to do work.
Heat that dissipates into the environment cannot be captured into more useful forms of energy.
According to 2nd law of thermodynamics, no process requiring energy conversion is ever 100% efficient.

8. Cells and Entropy
The second law of thermodynamics can be stated another way: every energy transformation makes the universe less organized and more disordered.
Entropy refers to the relative amount of disorganization.
The processes used by cells are energy transformations.

9. Cells and Entropy
Every process that occurs in cells increases the total entropy of the universe.
Cellular processes require an input of energy from an outside source.
For example, transport, biosynthesis
Ultimately, living organisms depend on a constant supply of energy from the sun.

10. Figure 6.2 H2O energy C6H12O6 CO2 Glucose Carbon dioxide and water
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H2O
energy
C6H12O6
CO2
Glucose
Carbon dioxide and water
• more organized
• less organized
• more potential energy
• less potential energy
• less stable (less entropy)
• more stable (more entropy) a.
Figure 6.2

11. Figure 6.2 H+ H+ channel protein H+ H+ H+ energy H+ H+ H+ H+ H+ H+ H+
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. H+ H+
channel protein H+ H+ H+
energy H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+
Unequal distribution
of hydrogen ions
Equal distribution
of hydrogen ions
• more organized
• less organized
• more potential energy
• less potential energy
• less stable (less entropy)
• more stable (more entropy) b.
Figure 6.2 11

12. Figure 6.2 12 H2O energy C6H12O6 CO2 Glucose Carbon dioxide and water
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H2O
energy
C6H12O6
CO2
Glucose
Carbon dioxide and water
• more organized
• less organized
• more potential energy
• less potential energy
• less stable (less entropy)
• more stable (more entropy) a. H+ H+
channel protein H+ H+
energy H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+
Unequal distribution
of hydrogen ions
Equal distribution
of hydrogen ions
• more organized
• less organized
• more potential energy
• less potential energy
• less stable (less entropy)
• more stable (more entropy) b.
Figure 6.2 12

13. 6.2 Energy Transformations and Metabolism
Metabolism is the sum of all the chemical reactions that occur in a cell.
The breaking down and building up of molecules is a large part of cellular metabolism.
Catabolism – …
Anabolism – …

14. 6.2 Energy Transformations and Metabolism
In a reaction:
A + B C + D
(reactants) (products)
Reactants are substances that participate in a reaction, while products are substances that form as a result of a reaction.

15. 6.2 Energy Transformations and Metabolism
Free energy (∆G) is the amount of energy available.
The change in free energy after a reaction is calculated by subtracting the free energy of the reactants from that of the products.
Reactions may have net free energies:
∆G = 0
∆G > 0
∆G < 0

16. 6.2 Energy Transformations and Metabolism
Exergonic reactions are ones where energy is released (∆G is negative).
Products have less free energy than reactants
Spontaneous
Endergonic reactions require an input of energy (∆G is positive).
Products have more free energy than reactants
Require an input of energy to run

17. ATP: Energy For Cells ATP stands for adenosine triphosphate
Common energy currency for cells
ATP generated from ADP (adenosine diphosphate) + an inorganic phosphate molecule P
ATP may be supplied because glucose breakdown provides the energy to build up ATP

18. adenosine triphosphate ATP is unstable and has
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adenosine triphosphate
ATP is unstable and has
a high potential energy. P P P
Endergonic Reaction:
• Creation of ATP from
ADP and P requires
input of energy from
other sources.
• Example: cellular
respiration
ATP
ADP + P
Exergonic Reaction:
• The hydrolysis of ATP releases previously stored energy, allowing
the change in free energy to do
work and drive other processes.
• Examples: protein synthesis, nerve
conduction, muscle contraction P P + P
adenosine diphosphate +
phosphate
ADP is more stable and has lower potential energy than ATP.

19. Structure of ATP ATP is a nucleotide composed of:
Adenine (a nitrogen-containing base)
Ribose (a 5-carbon sugar)
Three phosphate groups
Energy stored in these chemical bonds

20. Coupled Reactions Coupled Reactions
The energy released by an exergonic reaction is used to drive an endergonic reaction
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ATP
ADP + P
A + B
C + D
coupling

21. Copyright © The McGraw-Hill Companies, Inc
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1 Myosin assumes its
resting shape when
it combines with ATP.
2 ATP splits into ADP and , causing myosin to change its shape and allowing it to attach to actin. P
actin
ATP P
ADP
myosin

22. 3 Release of ADP and cause myosin to again change shape P
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3 Release of ADP and
cause myosin to
again change shape
and pull against actin,
generating force and
motion. P 22

23. 23 1 Myosin assumes its resting shape when it combines with ATP.
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1 Myosin assumes its
resting shape when
it combines with ATP.
3 Release of ADP and
cause myosin to
again change shape
and pull against actin,
generating force and
motion.
2 ATP splits into ADP and , causing myosin to change its shape and allowing it to attach to actin. P P
actin
ATP P
ADP
myosin 23

24. Function of ATP ATP can be used by cells for: Chemical work
Energy to synthesize macromolecules (anabolism)
Transport work
Energy to pump substances across membranes
Mechanical work
Energy to make muscles contract, cilia and flagella beat, and so forth

25. 6.3 Enzymes and Metabolic Pathways
Metabolic pathways are a series of linked reactions.
Reactions do not occur haphazardly in cells.
They begin with a specific reactant and produce an end product.
Metabolic energy is captured and utilized more easily because released in increments.
Pathways may connect through common intermediates.

26. 6.3 Enzymes and Metabolic Pathways
Typically proteins that function as catalysts to speed up chemical reactions
Ribozymes are RNA’s that can act as catalysts.
Participate in chemical reactions, but is not used up by the reaction
Do not cause reactions to go forward
Free energy determines which reactions go forward.

27. A Metabolic Pathway
Also called substrates

28. Energy of Activation (Ea)
Energy that must be added to cause reactants to react with one another
Need a match to start wood burning
Enzymes lower the energy of activation
Do not change the end result of the reaction
Increase the reaction rate

29. Figure 6.5 energy of activation (Ea) energy of energy of reactant
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energy of
activation (Ea)
energy of
reactant
energy of
activation (Ea)
Free Energy
energy of
product
enzyme not present
enzyme present
Progress of the Reaction
Figure 6.5

30. enzyme-substrate complex
How Enzymes Function
An enzyme binds with a substrate to form a complex.
The active site is a small part of the enzyme that complexes with the substrate.
The following equation indicates the sequence of steps in an enzyme-catalyzed reaction:
E + S  ES  E + P
enzyme
substrate
enzyme-substrate complex
enzyme
product

31. The substrate is broken down to smaller products. enzyme
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substrate
active site
Degradation
The substrate is broken
down to smaller products.
enzyme
Figure 6.6

32. enzyme-substrate complex
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substrate
enzyme-substrate
complex
active site
Degradation
The substrate is broken
down to smaller products.
enzyme
Figure 6.6 32

33. Substrate binds to active site on enzyme
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products
enzyme
substrate
enzyme-substrate
complex
active site
Degradation
The substrate is broken
down to smaller products.
enzyme
Substrate binds to active site on enzyme
Figure 6.6 33

34. The substrates are combined to produce a larger product. enzyme
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substrates
active site
Synthesis
The substrates are combined
to produce a larger product.
enzyme
Figure 6.6 34

35. enzyme-substrate complex
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substrates
enzyme-substrate
complex
active site
Synthesis
The substrates are combined
to produce a larger product.
enzyme
Figure 6.2 35

36. Figure 6.6 product enzyme substrates enzyme-substrate complex
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product
enzyme
substrates
enzyme-substrate
complex
active site
Synthesis
The substrates are combined
to produce a larger product.
enzyme
Figure 6.6 36

37. How Enzymes Function Induced fit model
Substrate and active site shapes do not fit together like a lock and key.
The active site undergoes a slight change in shape to accommodate substrate binding (induced fit).
The change in shape facilitates reaction by achieving optimum fit.
After reaction is completed, product(s) are released.

38. active site substrate a. b. Figure 6.7 38
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active site
substrate a. b.
Figure 6.7 38

39. How Enzymes Function Each reaction requires a specific enzyme.
Enzymes are often named for their substrate because they only complex with their substrate.
Substrate
Enzyme
Lipid
Lipase
Urea
Urease
Maltose
Maltase
Ribonucleic acid
Ribonuclease
Lactose
Lactase

40. Factors Affecting Enzymatic Speed
Enzymatic reactions proceed much more rapidly.
For example, breakdown of hydrogen peroxide is 600,000 times faster when the enzyme catalase is present.
The rate of enzymatic reaction may be influenced by:
Substrate Concentration
Temperature and pH
Enzyme Activation
Enzyme Inhibition
Enzyme Cofactors

41. Substrate Concentration
Enzyme activity increases as substrate concentration increases.
More collisions between substrate and enzyme
As more active sites are filled with substrate, more product will form
The maximum rate is achieved when all active sites of an enzyme are filled continuously with substrate.

42. Temperature and pH Enzyme activity increases as the temperature rises.
Higher temperatures cause more effective collisions between enzymes and substrates.
As temperature increases beyond a certain point, enzyme activity levels out.
At high temperatures, loss of structure and function occurs and enzyme is denatured
Decrease of temperature decreases enzyme activity

43. (product per unit of time)
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(product per unit of time)
Rate of Reaction
Temperature °C
a. Rate of reaction as a function of
temperature.
b. Body temperature of ectothermic
animals often limits rates of reactions.
c. Body temperature of endothermic animals
promotes rates of reactions.
b: © Brand X Pictures/PunchStock RF; c: © Digital Vision/PunchStock RF
Figure 6.8 43

44. Temperature and pH pH
Each enzyme has an optimal pH at which its activity is the highest.
Enzyme structure is also pH dependent.
Extremes of pH can denature an enzyme by altering its structure.
Preferred temperature of enzyme varies based on location (typsin and pepsin).

45. (product per unit of time)
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pepsin
trypsin
(product per unit of time)
Rate of Reaction 1 2 3 4 5 6 7 8 9 10 11 12 pH
Figure 6.9

46. Enzyme Activation Not all enzymes are needed all the time in a cell.P P
kinase
inactive protein
active protein
Not all enzymes are needed all the time in a cell.
Cell regulates metabolism by regulating which enzymes are active.
Genes producing enzymes can be turned on or off to regulate enzyme concentration.
Enzyme can be modified by adding or removing phosphates – changes shape.

47. Enzyme Inhibition Enzyme Inhibition
Inhibition occurs when substrate cannot bind to active site of enzyme.
Activity of almost every enzyme in a cell is regulated by feedback inhibition.

48. Enzyme Inhibition Simplest type of enzyme inhibition
When product is abundant it binds to enzyme’s active site and blocks further production
When product is used up, it is removed from the active site
Enzyme begins to function again

49. Enzyme Inhibition More complex enzyme inhibition
Product binds to a site other than the active site, which changes the shape of the active site.
Poisons are often enzyme inhibitors.
Cyanide inhibits an essential enzyme
Penicillin blocks the active site on a bacterial enzyme

50. first reactant A end product F
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first
reactant A E1
site of enzyme
where end product F
can bind E2 E3 E4 E5
end
product F A B C D E
a. Active pathway
Figure 6.10

51. end product F first reactant A end product F
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end
product F
altered site of
enzyme due to
binding of F E1
first
reactant A
end
product F
Reactant A cannot bind,
and no product results. E1
b. Inactive pathway
Figure 6.10 51

52. Figure 6.10 first reactant A E1 site of enzyme where end product F
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first
reactant A E1
site of enzyme
where end product F
can bind E2 E3 E4 E5
end
product F A B C D E
a. Active pathway
end
product F
altered site of
enzyme due to
binding of F E1
first
reactant A
end
product F
Reactant A cannot bind,
and no product results. E1
Figure 6.10
b. Inactive pathway 52

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54. Enzyme Cofactors
Enzymes require an inorganic ion or non- protein organic molecule to assist in reaction.
Inorganic ions such as copper, zinc or iron are examples of cofactors.
Organic non-protein cofactors are called coenzymes.
Vitamins are often components of coenzymes.

55. 6.4 Oxidation-Reduction Reactions and Metabolism
Oxidation is the loss of electrons.
Reduction is the gain of electrons.
Because these are usually coupled, the pair of reactions are referred to as redox reactions.
For example, when oxygen combines with Mg:
Oxygen gains electrons – becomes reduced
Mg loses electrons – becomes oxidized

56. Oxidation-Reduction Reactions
The term oxidation is used even when oxygen is not involved.
For example: Na+ + Cl-  NaCl
Sodium is oxidized
Chlorine is reduced

57. Oxidation-Reduction Reactions
The terms also apply to covalent reactions involving hydrogen atoms (e- + H+).
Oxidation is the loss of hydrogen atoms.
Loss of electrons
Reduction is the gain of hydrogen atoms.
Gain of electrons

58. Chloroplasts and Photosynthesis
Chloroplasts convert solar energy to ATP and use it to reduce carbon dioxide to carbohydrate.
Oxygen is a by-product that is released.
The overall equation for photosynthesis is:
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energy +
6 CO2 +
6 H2O
C6H12O6 +
6 O2
carbon
dioxide
water
glucose
oxygen

59. Mitochondria and Cellular Respiration
Mitochondria oxidize carbohydrates and use released energy to build ATP.
Oxygen is consumed and produces CO2 and water.
The overall equation is the opposite of the photosynthesis equation:
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C6H12O6 +
6 O2
6 CO2 +
6 H2O +
energy
glucose
oxygen
carbon
dioxide
water

60. Mitochondria and Cellular Respiration
Complete oxidation of a mole of glucose releases 686 kcal of energy
Some of the energy is harvested to form ATP.
Oxidation of glucose step-by-step allows energy to be gradually stored and then converted to make ATP.

61. (leaves): © Comstock/PunchStock RF; (runner): © PhotoDisc/Getty RF
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Photosynthesis
Cellular respiration
carbohydrate
sun O2
chloroplast
mitochondrion
heat
heat
CO2 + H2O
for synthetic
reactions, active
transport, muscle
contraction,
nerve impulse
ATP
heat
(leaves): © Comstock/PunchStock RF; (runner): © PhotoDisc/Getty RF

62. Cellular Respiration and Humans
Human beings are involved in the cycling of molecules between chloroplasts and mitochondria.
Our food is derived from plants or we eat animals that have eaten plants.
Food nutrients and oxygen enter mitochondria in our cells to produce ATP.
Without a supply of energy-rich molecules, derived ultimately from plants, we could not produce ATP.

63. Getty Images/SW Productions RF
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. O2
CO2
Breathing
Eating O2
CO2
Nutrients
ATP
Figure 6.12
Cellular respiration
Getty Images/SW Productions RF

64. Cellular Respiration and Humans
Though we have focused on the breakdown of glucose by cellular respiration, much of our diet should contain other nutrients
Food consists of carbohydrates, fats, and proteins
Broken down into simpler molecules in digestion
Can enter cellular respiration at various steps in the pathway to make ATP
Excess glucose can be used to form fatty acids
Fatty acids and glycerol form lipids or fat

65. Cellular Respiration and Humans
If we studied all the various metabolic steps in cellular respiration of glucose, fatty acids, and amino acids, we would realize that certain substrates recur in metabolism.
This allows the cell to switch metabolic gears and even switch to building molecules instead of breaking them down.