Biology 10th Edition by Raven

1. Chapter 06
Lecture and
Animation Outline
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2. 2
Energy and Metabolism
Chapter 6

3. 3
Flow of Energy
• Thermodynamics
– Branch of chemistry concerned with energy
changes
• Cells are governed by the laws of
physics and chemistry

4. • Energy – capacity to do work
– 2 states
1. Kinetic – energy of motion
2. Potential – stored energy
– Many forms – mechanical, heat, sound,
electric current, light, or radioactivity
– Heat the most convenient way of measuring
energy
• 1 calorie = heat required to raise 1 gram of water 1ºC
• calorie or Calorie?
4

5. 5
a. Potential energy b. Kinetic energy
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6. • Energy flows into the biological world from
the sun
• Photosynthetic organisms capture this
energy
• Stored as potential energy in chemical
bonds
6

7. 7
Redox reactions
• Oxidation
– Atom or molecule loses an electron
• Reduction
– Atom or molecule gains an electron
– Higher level of energy than oxidized form
• Oxidation-reduction reactions (redox)
– Reactions always paired

8. 8
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e–
A B
A + B +A+
B–
Loss of electron (oxidation)
Gain of electron (reduction)
Lower energy Higher energy

9. Laws of thermodynamics
• First law of thermodynamics
– Energy cannot be created or destroyed
– Energy can only change from one form to
another
– Total amount of energy in the universe
remains constant
– During each conversion, some energy is lost
as heat
9

10. 10
• Second law of thermodynamics
– Entropy (disorder) is continuously increasing
– Energy transformations proceed
spontaneously to convert matter from a more
ordered/less stable form to a less ordered/
more stable form

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Disorder happens
spontaneously
Organization
requires energy
© Jill Braaten

12. 12
Free energy
• G = Energy available to do work
• G = H – TS
 H = enthalpy, energy in a molecule’s chemical
bonds
 T = absolute temperature
 S = entropy, unavailable energy

13. ΔG = ΔH – TS
• ΔG = change in free energy
• Positive ΔG
– Products have more free energy than reactants
– H is higher or S is lower
– Not spontaneous, requires input of energy
– Endergonic
• Negative ΔG
– Products have less free energy than reactants
– H is lower or S is higher or both
– Spontaneous (may not be instantaneous)
– Exergonic 13

14. 14
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a.
b.
0
0
Course of Reaction
Products
∆ G > 0
∆ G < 0
Reactants
Reactants
Course of Reaction
Products
FreeEnergy(G)
EnergyReleasedEnergySupplied
FreeEnergy(G)
EnergyReleasedEnergySupplied
Energy is
released
Energy must
be supplied
Exergonic
Endergonic

15. Activation energy
• Extra energy required to destabilize existing
bonds and initiate a chemical reaction
• Exergonic reaction’s rate depends on the
activation energy required
– Larger activation energy proceeds more slowly
• Rate can be increased 2 ways
1.Increasing energy of reacting molecules (heating)
2.Lowering activation energy
15

16. 16
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ΔG
EnergyReleasedEnergySupplied
FreeEnergy(G)
Activation
energy
Activation
energy0
uncatalyzed
catalyzed
Course of Reaction
Product
Reactant

17. Catalysts
• Substances that influence chemical bonds
in a way that lowers activation energy
• Cannot violate laws of thermodynamics
– Cannot make an endergonic reaction
spontaneous
• Do not alter the proportion of reactant
turned into product
17

18. 18
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ΔG
EnergyReleasedEnergySupplied
FreeEnergy(G)
Activation
energy
Activation
energy0
uncatalyzed
catalyzed
Course of Reaction
Product
Reactant

19. 19
ATP
• Adenosine triphosphate
• Chief “currency” all cells use
• Composed of
– Ribose – 5 carbon sugar
– Adenine
– Chain of 3 phosphates
• Key to energy storage
• Bonds are unstable
• ADP – 2 phosphates
• AMP – 1 phosphate – lowest energy form

20. 20
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AMPCORE
O
O–
O
O
O
H
H H
H
O
CC
N
N
N
C
N
C
CH
H
P O–
O P
O P O
ADP
ATP
Triphosphate
group
O–
CH2
High-energy
bonds
a.
Adenine NH2
Ribose
OHOH
b.

21. 21
ATP cycle
• ATP hydrolysis drives endergonic
reactions
– Coupled reaction results in net –ΔG
(exergonic and spontaneous)
• ATP not suitable for long-term energy
storage
– Fats and carbohydrates better
– Cells store only a few seconds worth of ATP

22. 22
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+
+
Pi
Energy from
exergonic
cellular
reactions
ATP H2O
ADP
Energy for
endergonic
cellular
processes

23. 23
Enzymes: Biological Catalysts
• Most enzymes are protein
– Some are RNA
• Shape of enzyme stabilizes a temporary
association between substrates
• Enzyme not changed or consumed in
reaction
• Carbonic anhydrase
– 200 molecules of carbonic acid per hour made
without enzyme
– 600,000 molecules formed per second with enzyme

24. 24
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Active site
a. b.
Enzyme Enzyme–substrate complex
Substrate

25. Active site
• Pockets or clefts for substrate binding
• Forms enzyme–substrate complex
• Precise fit of substrate into active site
• Applies stress to distort particular bond to
lower activation energy
– Induced fit
25

26. 26
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1. The substrate, sucrose,
consists of glucose and
fructose bonded
together.
2. The substrate binds to the active site
of the enzyme, forming an enzyme–
substrate complex.
3. The binding of the substrate and
enzyme places stress on the glucose–
fructose bond, and the bond breaks.
4. Products are
released, and
the enzyme is
free to bind other
substrates.
Bond
Glucose
Fructose
Active site
Enzyme
sucrase
H2O

27. 27
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28. 28
• Enzymes may be suspended in the
cytoplasm or attached to cell membranes
and organelles
• Multienzyme complexes – subunits work
together to form molecular machine
– Product can be delivered easily to next
enzyme
– Unwanted side reactions prevented
– All reactions can be controlled as a unit

29. 29
Nonprotein enzymes
• Ribozymes
• 1981 discovery that certain reactions
catalyzed in cells by RNA molecule itself
1. 2 kinds
1. Intramolecular catalysis – catalyze reaction
on RNA molecule itself
2. Intermolecular catalysis – RNA acts on
another molecule

30. Enzyme function
• Rate of enzyme-catalyzed reaction
depends on concentrations of substrate
and enzyme
• Any chemical or physical condition that
affects the enzyme’s three-dimensional
shape can change rate
– Optimum temperature
– Optimum pH
30

31. 31
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a.
b.
RateofReaction
Optimum pH for pepsin
RateofReaction
pH of Reaction
Optimum pH for trypsin
1 2 3 4 5 6 7 8 9
30 40 50 60 70 80
Temperature of Reaction (˚C)
Optimum temperature
for human enzyme
Optimum temperature for enzyme
from hotsprings prokaryote

32. 32
Inhibitors
• Inhibitor – substance that binds to enzyme
and decreases its activity
• Competitive inhibitor
– Competes with substrate for active site
• Noncompetitive inhibitor
– Binds to enzyme at a site other than active
site
– Causes shape change that makes enzyme
unable to bind substrate

33. 33
a. Competitive inhibition b. Noncompetitive inhibition
Enzyme Enzyme
Allosteric site
Active
site
Competitive inhibitor interferes
with active site of enzyme so
substrate cannot bind
Allosteric inhibitor changes
shape of enzyme so it cannot
bind to substrate
Active
site
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Substrate Substrate
Inhibitor Inhibitor

34. 34
Allosteric Enzymes
• Allosteric enzymes – enzymes exist in
active and inactive forms
• Most noncompetitive inhibitors bind to
allosteric site – chemical on/off switch
• Allosteric inhibitor – binds to allosteric site
and reduces enzyme activity
• Allosteric activator – binds to allosteric site
and increases enzyme activity

35. 35
Metabolism
• Total of all chemical reactions carried out
by an organism
• Anabolic reactions/anabolism
– Expend energy to build up molecules
• Catabolic reactions/catabolism
– Harvest energy by breaking down molecules

36. 36
Biochemical pathways
• Reactions occur in a sequence
• Product of one reaction is the substrate for
the next
• Many steps take place in organelles

37. 37
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Initial substrate
Intermediate
substrate A
Intermediate
substrate B
Intermediate
substrate C
End product
Enzyme1
Enzyme2
Enzyme3
Enzyme4

38. Feedback inhibition
• End-product of pathway binds to an
allosteric site on enzyme that catalyzes
first reaction in pathway
• Shuts down pathway so raw materials and
energy are not wasted
38

39. 39
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a. b.
Enzyme 1
Enzyme 2
Enzyme 3
Enzyme 1
Enzyme 2
Enzyme 3End product End product
Initial
substrate
Intermediate
substrate A
Intermediate
substrate B
Initial
substrate

40. 40
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