Energy and Energy transfer
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Transcript of Energy and Energy transfer
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
ENERGY AND ENERGY TRANSFER
An Introduction to Metabolism
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Overview• Metabolism
• Exothermic/Endothermic reactions
• ATP
• Energy pyramids and ecosystems
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• Overview: The Energy of Life
• The living cell
– Is a miniature factory where thousands of reactions occur
– Converts energy in many ways
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• Metabolism
– Is the totality of an organism’s chemical reactions
– Arises from interactions between molecules
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Organization of the Chemistry of Life into Metabolic Pathways
• A metabolic pathway has many steps
– That begin with a specific molecule and end with a product
– That are each catalyzed by a specific enzyme
Enzyme 1 Enzyme 2 Enzyme 3A B C D
Reaction 1 Reaction 2 Reaction 3Starting
moleculeProduct
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• Catabolic pathways
– Break down complex molecules into simpler compounds
– Release energy
• Anabolic pathways
– Build complicated molecules from simpler ones
– Consume energy
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• Thermodynamics
– Is the study of energy transformations
An organism’s metabolism transforms matter and energy, subject to the laws of thermodynamics
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The First and Second Laws of Thermodynamics• According to the first law of thermodynamics
– Energy can be transferred and transformed
– Energy cannot be created or destroyed
• According to the second law of thermodynamics– Spontaneous changes that do not require outside
energy increase the entropy, or disorder, of the universe
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• Concept 8.2: The free-energy change of a reaction tells us whether the reaction occurs spontaneously
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Free-Energy Change, G• A living system’s free energy
– Is energy that can do work under cellular conditions
• The change in free energy, ∆G during a biological process
– Is related directly to the enthalpy change (∆H) and the change in entropy
– ∆G = ∆H – T∆S
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Free Energy, Stability, and Equilibrium• Organisms live at the expense of free energy
• During a spontaneous change
– Free energy decreases and the stability of a system increases
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Exergonic and Endergonic Reactions in Metabolism
• An exergonic reaction
– Proceeds with a net release of free energy and is spontaneous
Figure 8.6
Reactants
ProductsEnergy
Progress of the reaction
Amount ofenergyreleased (∆G <0)
Free
ene
rgy
(a) Exergonic reaction: energy released
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• An endergonic reaction
– Is one that absorbs free energy from its surroundings and is nonspontaneous
Figure 8.6
Energy
Products
Amount ofenergyreleased (∆G>0)
Reactants
Progress of the reaction
Free
ene
rgy
(b) Endergonic reaction: energy required
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Equilibrium and Metabolism• Reactions in a closed system
– Eventually reach equilibrium
Figure 8.7 A
(a) A closed hydroelectric system. Water flowing downhill turns a turbine that drives a generator providing electricity to a light bulb, but only until the system reaches equilibrium.
∆G < 0 ∆G = 0
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• Cells in our body
– Experience a constant flow of materials in and out, preventing metabolic pathways from reaching equilibrium
Figure 8.7
(b) An open hydroelectric system. Flowing water keeps driving the generator because intake and outflow of water keep the system from reaching equlibrium.
∆G < 0
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• An analogy for cellular respiration
Figure 8.7 (c) A multistep open hydroelectric system. Cellular respiration is analogous to this system: Glucoce is brocken down in a series of exergonic reactions that power the work of the cell. The product of each reaction becomes the reactant for the next, so no reaction reaches equilibrium.
∆G < 0∆G < 0
∆G < 0
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• Concept 8.3: ATP powers cellular work by coupling exergonic reactions to endergonic reactions
• A cell does three main kinds of work
– Mechanical
– Transport
– Chemical
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The Structure and Hydrolysis of ATP• ATP (adenosine triphosphate)
– Is the cell’s energy shuttle
– Provides energy for cellular functions
Figure 8.8
O O O O CH2
H
OH OH
H
N
H H
ON C
HC
N CC
N
NH2Adenine
RibosePhosphate groups
O
O O
O
O
O
-- - -
CH
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Structure of ATP• Phosphate – phosphate bonds
– Negative charges repel, unstable
– “high transferable energy”
– C-C ~400 KJ/mol while P-P 7.3 KJ/mol
– Right amount for most chemical reactions
• Each cell contains one billion ATP
• Short term storage
• Controlled production
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• Energy is released from ATP
– When the terminal phosphate bond is broken
Figure 8.9
P
Adenosine triphosphate (ATP)
H2O
+ Energy
Inorganic phosphate Adenosine diphosphate (ADP)
PP
P PP i
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• The three types of cellular work– Are powered by the hydrolysis of ATP
(c) Chemical work: ATP phosphorylates key reactants
P
Membraneprotein
Motor protein
P i
Protein moved(a) Mechanical work: ATP phosphorylates motor proteins
ATP
(b) Transport work: ATP phosphorylates transport proteinsSolute
P P i
transportedSolute
Glu GluNH3
NH2P i
P i
+ +
Reactants: Glutamic acid and ammonia
Product (glutamine)made
ADP+
P
Figure 8.11
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The Regeneration of ATP• Catabolic pathways
– Drive the regeneration of ATP from ADP and phosphate
ATP synthesis from ADP + P i requires energy
ATP
ADP + P i
Energy for cellular work(endergonic, energy-consuming processes)
Energy from catabolism(exergonic, energy yieldingprocesses)
ATP hydrolysis to ADP + P i yields energy
Figure 8.12
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• Concept 8.4: Enzymes speed up metabolic reactions by lowering energy barriers
• A catalyst
– Is a chemical agent that speeds up a reaction without being consumed by the reaction
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• An enzyme
– Is a catalytic protein
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• The activation energy, EA
– Is the initial amount of energy needed to start a chemical reaction
– Is often supplied in the form of heat from the surroundings in a system
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• The effect of enzymes on reaction rate
Progress of the reaction
Products
Course of reaction without enzyme
Reactants
Course of reaction with enzyme
EA
withoutenzyme
EA with enzymeis lower
∆G is unaffected by enzymeFr
ee e
nerg
y
Figure 8.15
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• The active site can lower an EA barrier by
– Orienting substrates correctly
– Straining substrate bonds
– Providing a favorable microenvironment
– Covalently bonding to the substrate
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• Concept 8.5: Regulation of enzyme activity helps control metabolism
• A cell’s metabolic pathways
– Must be tightly regulated
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• Energy
– Flows into an ecosystem as sunlight and leaves as heat
Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesisin chloroplasts
Cellular respiration
in mitochondria
Organicmolecules+ O2
ATP
powers most cellular work
HeatenergyFigure 9.2
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• Some redox reactions
– Do not completely exchange electrons
– Change the degree of electron sharing in covalent bonds
CH4
H
H
HH C O O O O OC
H H
Methane(reducingagent)
Oxygen(oxidizingagent)
Carbon dioxide Water
+ 2O2 CO2 + Energy + 2 H2O
becomes oxidized
becomes reduced
Reactants Products
Figure 9.3
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Oxidation of Organic Fuel Molecules During Cellular Respiration
• During cellular respiration
– Glucose is oxidized in a series of steps and oxygen is reduced
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
becomes oxidized
becomes reduced
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• Electrons from organic compounds
– Are usually first transferred to NAD+, a coenzyme
NAD+H
O
OO O
–OO O
–O
O
O
P
P
CH2
CH2
HO OHH
HHO OH
HO
H
H
N+
C NH2
HN
H
NH2
N
N
Nicotinamide(oxidized form)
NH2+ 2[H](from food)
DehydrogenaseReduction of
NAD+Oxidation of NADH
2 e– + 2 H+2 e– + H+
NADHOH H
NC +
Nicotinamide(reduced form)
N
Figure 9.4
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• NADH, the reduced form of NAD+
– Passes the electrons to the electron transport chain
• At the end of the chain
– Electrons are passed to oxygen, forming water
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• There are three main processes in this metabolic enterprise
Electron shuttlesspan membrane
CYTOSOL 2 NADH
2 FADH2
2 NADH 6 NADH 2 FADH22 NADH
Glycolysis
Glucose2
Pyruvate
2AcetylCoA
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
MITOCHONDRION
by substrate-levelphosphorylation
by substrate-levelphosphorylation
by oxidative phosphorylation, dependingon which shuttle transports electronsfrom NADH in cytosol
Maximum per glucose:About
36 or 38 ATP
+ 2 ATP + 2 ATP + about 32 or 34 ATP
or
Figure 9.16
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Excitation of Chlorophyll by Light• When a pigment absorbs light
– It goes from a ground state to an excited state, which is unstable
Excitedstate
Ene
rgy
of e
lect
ion
Heat
Photon(fluorescence)
Chlorophyllmolecule
GroundstatePhoton
e–
Figure 10.11 A
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• Produces NADPH, ATP, and oxygen
Figure 10.13 Photosystem II(PS II)
Photosystem-I(PS I)
ATP
NADPH
NADP+
ADP
CALVINCYCLE
CO2H2O
O2 [CH2O] (sugar)
LIGHTREACTIONS
Light
Primaryacceptor
Pq
Cytochromecomplex
PC
e
P680
e–
e–
O2
+
H2O2 H+
Light
ATP
Primaryacceptor
Fd
ee–
NADP+
reductase
ElectronTransportchain
Electron transport chain
P700
Light
NADPH
NADP+
+ 2 H+
+ H+
1
5
7
2
3
4
6
8
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A Comparison of Chemiosmosis in Chloroplasts and Mitochondria
• Chloroplasts and mitochondria
– Generate ATP by the same basic mechanism: chemiosmosis
– But use different sources of energy to accomplish this
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• Concept 10.3: The Calvin cycle uses ATP and NADPH to convert CO2 to sugar
• The Calvin cycle
– Is similar to the citric acid cycle
– Occurs in the stroma
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• The Calvin cycle
(G3P)
Input(Entering one
at a time)CO2
3
Rubisco
Short-livedintermediate
3 P P
3 P PRibulose bisphosphate
(RuBP)
P
3-Phosphoglycerate
P6 P
6
1,3-Bisphoglycerate6 NADPH
6 NADPH+
6 P
P6
Glyceraldehyde-3-phosphate(G3P)
6 ATP
3 ATP
3 ADP CALVINCYCLE
P5
P1G3P
(a sugar)Output
LightH2O CO2
LIGHTREACTION
ATP
NADPH
NADP+
ADP
[CH2O] (sugar)
CALVINCYCLE
Figure 10.18
O2
6 ADP
Glucose andother organiccompounds
Phase 1: Carbon fixation
Phase 2:Reduction
Phase 3:Regeneration ofthe CO2 acceptor(RuBP)
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• Overview: Ecosystems, Energy, and Matter
• An ecosystem consists of all the organisms living in a community
– As well as all the abiotic factors with which they interact
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• Concept 54.1: Ecosystem ecology emphasizes energy flow and chemical cycling
• Ecosystem ecologists view ecosystems
– As transformers of energy and processors of matter
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Ecosystems and Physical Laws• The laws of physics and chemistry apply to
ecosystems
– Particularly in regard to the flow of energy
• Energy is conserved
– But degraded to heat during ecosystem processes
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• Energy flows through an ecosystem
– Entering as light and exiting as heat
Figure 54.2
Microorganismsand other
detritivores
Detritus
Primary producers
Primary consumers
Secondaryconsumers
Tertiary consumers
Heat
Sun
Key
Chemical cyclingEnergy flow
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• Concept 54.2: Physical and chemical factors limit primary production in ecosystems
• Primary production in an ecosystem
– Is the amount of light energy converted to chemical energy by autotrophs during a given time period
• The extent of photosynthetic production
– Sets the spending limit for the energy budget of the entire ecosystem
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Gross and Net Primary Production• Total primary production in an ecosystem
– Is known as that ecosystem’s gross primary production (GPP)
• Not all of this production– Is stored as organic material in the growing plants
• Net primary production (NPP)– Is equal to GPP minus the energy used by the primary
producers for respiration
• Only NPP– Is available to consumers
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Pyramids of Production• This loss of energy with each transfer in a food chain
– Can be represented by a pyramid of net production
Figure 54.11
Tertiaryconsumers
Secondaryconsumers
Primaryconsumers
Primaryproducers
1,000,000 J of sunlight
10 J
100 J
1,000 J
10,000 J
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Pyramids of Numbers• A pyramid of numbers
– Represents the number of individual organisms in each trophic level
Figure 54.13
Trophic level Number of individual organisms
Primary producers
Tertiary consumers
Secondary consumers
Primary consumers
3
354,904
708,624
5,842,424
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• Worldwide agriculture could successfully feed many more people
– If humans all fed more efficiently, eating only plant material
Figure 54.14
Trophic level
Secondaryconsumers
Primaryconsumers
Primaryproducers
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• In biological magnification– Toxins concentrate at higher trophic levels
because at these levels biomass tends to be lower
Figure 54.23
Con
cent
ratio
n of
PC
Bs
Herringgull eggs124 ppm
Zooplankton 0.123 ppm
Phytoplankton 0.025 ppm
Lake trout 4.83 ppm
Smelt 1.04 ppm