1. Chapter 6 Energy Flow in the Life of a Cell
Copyright © 2005 Pearson Prentice Hall, Inc.

2. Figure: 6-CO
Title:
Energy Flow in the Life of a Cell
Caption:
The bodies of these runners efficiently convert energy stored in fats and carbohydrates to the energy of movement and heat. Their pounding footsteps noticeably shake the Verrazano Bridge during the New York Marathon.

3. OR “YOU CAN’T BREAK EVEN”
Energy?
ABILITY TO DO WORK
potential (stored) kinetic (active) (the diver illustration)
“Acts” According to 2 “Rules”
First Law of Thermodynamics
Energy Cannot be Created or Destroyed OR
Energy Can Only be Converted from 1 Form to Another
OR “YOU CAN’T WIN”
Second Law of Thermodynamics
Every Process Generates Some Unusable Energy (= Heat) OR
Every System “Wants” To Get To Its Lowest Energy State
OR “YOU CAN’T BREAK EVEN”
Organisms Are Organized = High Energy State
2nd Law Constantly “Driving Them Down”
Therefore Organisms Constanly Use Energy to Stay Organized
Copyright © 2005 Pearson Prentice Hall, Inc.

4. Figure :6-1
Title:
From potential to kinetic energy
Caption:
Perched atop the platform, the body of the diver has potential energy, because the heights of the platform and the pool are different. As he dives, the potential energy is converted to the kinetic energy of motion of the diver's body. Finally, some of this kinetic energy is transferred to the water, which itself is set in motion.

5. Energy? ABILITY TO DO WORK “Acts” According to 2 “Rules”
potential (stored) kinetic (active) Unnumbered (diver)
“Acts” According to 2 “Rules”
First Law of Thermodynamics
Energy Cannot be Created or Destroyed
Energy Can Only be Converted from 1 Form to Another
“YOU CAN’T WIN”
Second Law of Thermodynamics
Every Process Generates Unusable Energy (= Heat)
Every System “Wants” To Get To Its Lowest Energy State
“YOU CAN’T BREAK EVEN”
Organisms Are Organized = High Energy State
2nd Law Constantly “Driving Them Down”
Therefore Organisms Constanly Use Energy to Stay Organized
Copyright © 2005 Pearson Prentice Hall, Inc.

6. 100 units chemical energy (concentrated) gas 25 units kinetic energy
(motion)
75 units heat
energy
Figure: 6-UN1
Title:
First Law of Thermodynamics example
Caption:
The first law of thermodynamics states that, assuming there is no influx of energy, the total amount of energy within a given system remains constant.

7. How Do Organisms Constantly Use Energy to Stay Organized?
By Reaction Coupling 2 Types of Reactions:
Exergonic – Release Energy
Endergonic – Take In Energy
Energy relations in exergonic and endergonic reactions
Organisms Use the Energy of Sunlight to Maintain The Highly Organized (=Low-Entropy) Condition Known as Life
Carry Out Reaction Coupling By Energy Carriers:
Copyright © 2005 Pearson Prentice Hall, Inc.

8. Exergonic reaction energy released reactants products Figure: 6-UN2
Title:
Exergonic reaction

9. Endergonic reaction energy used products reactants Figure: 6-UN3
Title:
Endergonic reaction

10. Burning glucose glucose oxygen O 6 energy released O H 6 water C
carbon
dioxide
Figure: 6-UN4
Title:
Burning glucose

11. Photosynthesis O H 6 water energy C carbon dioxide glucose O 6 oxygen
Figure: 6-UN5
Title:
Photosynthesis

12. Burning glucose (sugar): an exergonic reaction
Photosynthesis: an endergonic reaction
high
high
activation energy needed
to ignite glucose
glucose
activation
energy from
light captured
by photosynthesis
glucose + O2
energy
content of
molecules
energy
content of
molecules
net energy
captured by
synthesizing
glucose
energy released
by burning glucose
CO2 + H2O
CO2 + H2O
low
low
progress of reaction
progress of reaction
Figure :6-2
Title:
Energy relations in exergonic and endergonic reactions
Caption:
(a) An exergonic (downhill) reaction, such as the burning of sugar, proceeds from high-energy reactants (here, glucose) to low-energy products (CO2 and H2O). The energy difference between the chemical bonds of the reactants and products is released as heat. To start the reaction, however, an initial input of energy—the activation energy—is required. (b) An endergonic (uphill) reaction, such as photosynthesis, proceeds from low-energy reactants (CO2 and H2O) to high-energy products (glucose) and therefore requires a net input of energy, in this case from sunlight. Question In addition to heat and sunlight, what are some other potential sources of activation energy?

13. relaxed muscle Exergonic reaction: Endergonic reaction:
Coupled reaction:
20 units
energy
ATP
contracted
muscle
100 units
energy released
80 units energy
released as heat
ADP P
Figure :6-3
Title:
Coupled reactions
Caption:
Muscle movement requires an endergonic reaction coupled to the exergonic reaction of ATP breakdown; the overall reaction is exergonic. (Energy units are arbitrary.)

14. Exergonic reaction: ATP 100 units energy released + ADP + P
Endergonic reaction: +
20 units
energy
relaxed
muscle
contracted
muslce
Coupled reaction: + + + +
ATP
80 units energy
released as heat
ADP P
Figure :6-3
Title:
Coupled reactions
Caption:
Muscle movement requires an endergonic reaction coupled to the exergonic reaction of ATP breakdown; the overall reaction is exergonic. (Energy units are arbitrary.)
relaxed
muscle
contracted
muslce

15. 6.3 How Is Cellular Energy Carried Between Coupled Reactions?
ATP Is the Principal Energy Carrier in Cells
Figure 6.4 ADP and ATP (p. 104)
Unnumbered Figure 6 (Hide/Reveal) ATP synthesis: Energy is stored in ATP (p. 104)
Unnumbered Figure 7 (Hide/Reveal) ATP breakdown: Energy of ATP is released (p. 104)
Figure 6.5 Coupled reactions within living cells (p. 105)
Copyright © 2005 Pearson Prentice Hall, Inc.

16. Shorthand representations
Adenosine diphosphate (ADP)
Adenosine triphosphate (ATP)
NH2
NH2
adenine
"high-energy”
bond 2
"high-energy”
bonds C C N N C N C N HC HC C CH C CH N N N N O– O– O O– O– O O–
ribose
CH2 O P O P O–
CH2 O P O P O P O – H H H H H O O H H H O O O OH OH
phosphate groups OH OH
phosphate groups
Shorthand
representations A P P or
ADP A P P P or
ATP
Figure :6-4
Title:
ADP and ATP
Caption:
A phosphate group is added to (a) ADP (adenosine diphosphate) to make (b) ATP (adenosine triphosphate). In most cases, only the last phosphate group and its high-energy bond are used to carry energy and transfer it to endergonic reactions within a cell. Question Why does conversion of ATP to ADP release energy for cellular work?
Energy
content
low
high

17. Shorthand representations
Adenosine diphosphate (ADP)
NH2
adenine
"high-energy”
bond C N C N HC C CH N N O– O– O
CH2 O
ribose P O P O– H H H H O O OH OH
phosphate groups
Figure :6-4 part a
Title:
ADP and ATP part a Adenosine diphosphate (ADP)
Caption:
A phosphate group is added to (a) ADP (adenosine diphosphate) to make (b) ATP (adenosine triphosphate). In most cases, only the last phosphate group and its high-energy bond are used to carry energy and transfer it to endergonic reactions within a cell. Question Why does conversion of ATP to ADP release energy for cellular work?
Shorthand
representations A P P or
ADP
Energy
content
low

18. Adenosine triphosphate (ATP)
NH2
"high-energy”
bonds C N C N HC C CH N N O– O– O– O
CH2 O P O P O P O– H H H H O O O OH OH
phosphate groups
Figure :6-4 part b
Title:
ADP and ATP part b Adenosine triphosphate (ATP)
Caption:
A phosphate group is added to (a) ADP (adenosine diphosphate) to make (b) ATP (adenosine triphosphate). In most cases, only the last phosphate group and its high-energy bond are used to carry energy and transfer it to endergonic reactions within a cell. Question Why does conversion of ATP to ADP release energy for cellular work? A P P P or
ATP
high

19. ATP synthesis: Energy is stored in ATP
ADP A P
phosphate
ATP A P
Figure: 6-UN6
Title:
ATP synthesis: Energy is stored in ATP

20. ATP synthesis: Energy is stored in ATP
Figure: 6-UN6
Title:
ATP synthesis: Energy is stored in ATP
ADP
phosphate

21. ATP breakdown: Energy of ATP is released
ADP A P
phosphate
Figure: 6-UN7
Title:
ATP breakdown: Energy of ATP is released

22. ATP breakdown: Energy of ATP is released
Figure: 6-UN7
Title:
ATP breakdown: Energy of ATP is released
ADP
phosphate

23. Coupled reaction: glucose breakdown and protein synthesis
exergonic
(glucose
breakdown)
endergonic
(ATP synthesis)
protein
exergonic
(ATP breakdown)
endergonic
(protein synthesis)
CO2 + H2O + heat
Figure :6-5
Title:
Coupled reactions within living cells
Caption:
Exergonic reactions (such as glucose breakdown) drive the endergonic reaction of synthesizing ATP from ADP. The ATP molecule then moves to a part of the cell where the energy from the breakdown of ATP is needed to drive an essential endergonic reaction (such as protein synthesis). The ADP and phosphate are recycled back to ATP via endergonic reactions. The overall reaction is exergonic, or "downhill": more energy is released by the exergonic reaction than is needed to drive the endergonic reaction. A P P P
ADP
amino
acids
heat
net exergonic
"downhill" reaction

24. 6.3 How Is Cellular Energy Carried Between Coupled Reactions?
Electron Carriers Also Transport Energy Within Cells
Figure 6.6 Electron carriers (p. 105)
Copyright © 2005 Pearson Prentice Hall, Inc.

25. Electron carrier molecules transport energy
NADH
exergonic
reaction
(energized
carrier) e_ e_
(depleted
carrier)
endergonic
reaction
Figure :6-6
Title:
Electron carriers
Caption:
Electron-carrier molecules such as NAD+ pick up electrons generated by exergonic reactions and hold them in high-energy outer electron shells. Hydrogen atoms are often picked up simultaneously. The electron is then deposited, energy and all, with another molecule to drive an endergonic reaction, typically the synthesis of ATP.
NAD+ H
net exergonic
"downhill" reaction

26. 6.4 How Do Cells Control Their Metabolic Reactions?
Figure 6.7 Simplified view of metabolic pathways (p. 106)
Copyright © 2005 Pearson Prentice Hall, Inc.

27. Initial reactant Intermediates Final products PATHWAY 1 A B C D E
enzyme 1
enzyme 2
enzyme 3
enzyme 4
PATHWAY 2 F G
enzyme 5
enzyme 6
Figure :6-7
Title:
Simplified view of metabolic pathways
Caption:
The original reactant molecule, A, undergoes a series of reactions, each catalyzed by a specific enzyme. The product of each reaction serves as the reactant for the next reaction in the pathway. Metabolic pathways are commonly interconnected such that the product of a step in one pathway may serve as a reactant for the next reaction in that pathway or for a reaction in another pathway.

28. 6.4 How Do Cells Control Their Metabolic Reactions?
At Body Temperatures, Spontaneous Reactions Proceed Too Slowly to Sustain Life
Catalysts Reduce Activation Energy
Figure 6.8 Catalysts lower activation energy, increasing the rate of reactions (p. 106)
Copyright © 2005 Pearson Prentice Hall, Inc.

29. high energy content of molecules reactants products low
activation energy
without
catalyst
activation energy
with catalyst
energy
content of
molecules
reactants
Figure :6-8
Title:
Catalysts lower activation energy, increasing the rate of reactions
Caption:
A high activation energy (black curve) means that reactant molecules must collide very forcefully in order to react. Only very fast-moving molecules will collide hard enough to react, so reactions with high activation energies proceed slowly at low temperatures, where most molecules move relatively slowly. Catalysts lower the activation energy of a reaction (red curve), so a much higher proportion of molecules move fast enough to react when they collide. Therefore, the reaction proceeds much more rapidly. Question Can a catalyst make a non-spontaneous reaction occur spontaneously?
products
low
progress of reaction

30. 6.4 How Do Cells Control Their Metabolic Reactions?
Enzymes Are Biological Catalysts
The Structure of Enzymes Allows Them to Catalyze Specific Reactions
Figure 6.9 The cycle of enzyme–substrate interactions (p. 107)
Copyright © 2005 Pearson Prentice Hall, Inc.

31. substrates active site of enzyme enzyme Figure :6-9 Title:
The cycle of enzyme–substrate interactions
Caption:
Question How would you modify reaction conditions if you wanted to increase the rate at which an enzyme-catalyzed reaction produced its product?

32. substrates active site of enzyme enzyme Figure :6-9 Title:
The cycle of enzyme–substrate interactions
Caption:
Question How would you modify reaction conditions if you wanted to increase the rate at which an enzyme-catalyzed reaction produced its product?

33. 6.4 How Do Cells Control Their Metabolic Reactions?
Cells Regulate the Amount and the Activity of Their Enzymes
Figure Enzyme regulation by feedback inhibition (p. 108)
Figure Enzyme regulation by allosteric regulation and competitive inhibition (p. 109)
Copyright © 2005 Pearson Prentice Hall, Inc.

34. enzyme 1 enzyme 2 enzyme 3 enzyme 4 enzyme 5 CH3 CH3 CH2 H C OH A B CD H C
CH3
enzyme 1
enzyme 2
enzyme 3
enzyme 4
enzyme 5 H C
NH3 H C
NH3
COOH
COOH
Feedback inhibition:
Isoleucine inhibits enzyme 1
threonine
(substrate amino acid)
isoleucine
(end-product amino acid)
Figure :6-10
Title:
Enzyme regulation by feedback inhibition
Caption:
In this example, the first enzyme in the metabolic pathway that converts threonine (an amino acid substrate) to isoleucine (an amino acid product) is inhibited by high concentrations of isoleucine. If a cell lacks isoleucine, the first enzyme is not inhibited, and the pathway proceeds rapidly. As isoleucine concentrations build up, the isoleucine binds to the first enzyme and gradually shuts down the pathway. When concentrations of isoleucine drop and fewer molecules are available to inhibit the enzyme, the pathway resumes production.

35. Enzyme structure Allosteric inhibition Competitive inhibition
active site
substrate
enzyme
allosteric
regulatory site
allosteric
regulator
molecule
Allosteric
inhibition
Figure :6-11
Title:
Enzyme regulation by allosteric regulation and competitive inhibition
Caption:
(a) Many enzymes have an active site and an allosteric regulatory site on different parts of the molecule. (b) When enzymes are inhibited by allosteric regulation, binding by a regulator molecule alters the active site so the enzyme is less compatible with its substrate. (c) During competitive inhibition, a molecule somewhat similar to the substrate fits into the active site and blocks entry of the substrate.
Competitive
inhibition

36. Enzyme structure Allosteric inhibition Competitive inhibition
substrate
active site
enzyme
allosteric
regulatory site
Allosteric
inhibition
Figure :6-11
Title:
Enzyme regulation by allosteric regulation and competitive inhibition
Caption:
(a) Many enzymes have an active site and an allosteric regulatory site on different parts of the molecule. (b) When enzymes are inhibited by allosteric regulation, binding by a regulator molecule alters the active site so the enzyme is less compatible with its substrate. (c) During competitive inhibition, a molecule somewhat similar to the substrate fits into the active site and blocks entry of the substrate.
allosteric
regulator
molecule
Competitive
inhibition

37. 6.4 How Do Cells Control Their Metabolic Reactions?
The Activity of Enzymes Is Influenced by Their Environment
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