ENERGY AND ENERGY

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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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


Overview: The Energy of Life


The living cell


Is a miniature factory where thousands of
reactions occur


Converts energy in many ways

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


Metabolism


Is the totality of an organism’s chemical
reactions


Arises from interactions between molecules

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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 3

A

B

C

D

Reaction 1

Reaction 2

Reaction 3

Starting

molecule

Product

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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


Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


Thermodynamics


Is the study of energy transformations

An
organism’s metabolism transforms matter and
energy, subject to the laws of thermodynamics

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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


Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


Concept 8.2: The free
-
energy change of a
reaction tells us whether the reaction occurs
spontaneously

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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



Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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

Products

Energy

Progress of the reaction

Amount of

energy

released

(∆
G

<0)

Free energy

(a) Exergonic reaction: energy released

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


An endergonic reaction


Is one that absorbs free energy from its
surroundings and is nonspontaneous

Figure 8.6

Energy

Products

Amount of

energy

released

(∆
G
>0)

Reactants

Progress of the reaction

Free energy

(b) Endergonic reaction: energy required

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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

CH
2

H

OH

OH

H



N

H


H


O

N

C

HC

N

C

C

N

NH
2

Adenine

Ribose

Phosphate 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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


Energy is released from ATP


When the terminal phosphate bond is broken

Figure 8.9

P

Adenosine triphosphate (ATP)

H
2
O

+

Energy

Inorganic phosphate

Adenosine diphosphate (ADP)

P

P

P

P

P
i

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


The three types of cellular work


Are powered by the hydrolysis of ATP

(c) Chemical work: ATP phosphorylates key reactants

P

Membrane

protein

Motor protein

P
i

Protein moved

(a) Mechanical work: ATP phosphorylates motor proteins

ATP

(b) Transport work: ATP phosphorylates transport proteins

Solute

P

P
i

transported

Solute

Glu

Glu


NH
3

NH
2

P
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 yielding

processes)

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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


The activation energy, E
A


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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


The effect of enzymes on reaction rate

Progress of the reaction

Products

Course of

reaction

without

enzyme

Reactants

Course of

reaction

with enzyme

E
A

without

enzyme

E
A
with

enzyme

is lower


G

is unaffected

by enzyme

Free energy

Figure 8.15

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The active site can lower an E
A

barrier by


Orienting substrates correctly


Straining substrate bonds


Providing a favorable microenvironment


Covalently bonding to the substrate

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


Concept 8.5: Regulation of enzyme activity
helps control metabolism


A cell’s metabolic pathways


Must be tightly regulated

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


Energy


Flows into an ecosystem as sunlight and
leaves as heat

Light energy

ECOSYSTEM

CO
2

+ H
2
O

Photosynthesis

in chloroplasts

Cellular
respiration

in mitochondria

Organic

molecules

+ O
2

ATP

powers most cellular work

Heat

energy

Figure 9.2

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


Some redox reactions


Do not completely exchange electrons


Change the degree of electron sharing in
covalent bonds

CH
4


H


H


H


H

C

O

O

O

O

O

C


H


H

Methane

(reducing

agent)

Oxygen

(oxidizing

agent)

Carbon dioxide

Water

+

2O
2

CO
2

+

Energy

+

2 H
2
O

becomes oxidized

becomes reduced

Reactants

Products

Figure 9.3

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Oxidation of Organic Fuel Molecules During
Cellular Respiration


During cellular respiration


Glucose is oxidized
in a series of steps and
oxygen is
reduced

C
6
H
12
O
6

+ 6O
2

6CO
2

+ 6H
2
O + Energy

becomes oxidized

becomes reduced

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


Electrons from organic compounds


Are usually first transferred to NAD
+
, a
coenzyme

NAD
+


H

O

O

O

O


O

O

O


O

O

O

P

P

CH
2

CH
2

HO

OH

H

H

HO

OH

HO

H

H

N
+

C

NH
2

H

N

H

NH
2

N

N

Nicotinamide

(oxidized form)

NH
2

+

2[H]

(from
food)

Dehydrogen
ase

Reduction of
NAD
+

Oxidation of
NADH

2 e


+ 2 H
+

2 e


+ H
+

NADH

O

H

H

N

C

+

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


Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


There are three main processes in this
metabolic enterprise

Electron shuttles

span membrane

CYTOSOL

2 NADH

2 FADH
2

2 NADH

6 NADH

2 FADH
2

2 NADH

Glycolysis

Glucose

2

Pyruvate

2

Acetyl

CoA

Citric

acid

cycle

Oxidative

phosphorylation:

electron transport

and

chemiosmosis

MITOCHONDRION

by substrate
-
level

phosphorylation

by substrate
-
level

phosphorylation

by oxidative phosphorylation, depending

on which shuttle transports electrons

from 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

Excited

state

Heat

Photon

(fluorescence)

Chlorophyll

molecule

Ground

state

Photon

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

CALVIN

CYCLE

CO
2

H
2
O

O
2

[CH
2
O] (sugar)

LIGHT

REACTIONS

Light

Primary

acceptor

Pq

Cytochrome

complex

PC

e

P680

e


e


O
2

+

H
2
O

2 H
+

Light

ATP

Primary

acceptor

Fd

e

e


NADP
+

reductase

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 CO
2

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)

CO
2

3

Rubisco

Short
-
lived

intermediate

3 P

P

3 P

P

Ribulose bisphosphate

(RuBP)

P

3
-
Phosphoglycerate

P

6 P

6

1,3
-
Bisphoglycerate

6 NADPH

6 NADPH
+

6 P

P

6

Glyceraldehyde
-
3
-
phosphate

(G3P)

6 ATP

3 ATP

3 ADP

CALVIN

CYCLE

P

5

P

1

G3P

(a sugar)

Output

Light

H
2
O

CO
2

LIGHT

REACTION

ATP

NADPH

NADP
+

ADP

[CH
2
O] (sugar)

CALVIN

CYCLE

Figure 10.18

O
2

6 ADP

Glucose and

other organic

compounds

Phase 1: Carbon fixation

Phase 2:

Reduction

Phase 3:

Regeneration of

the CO
2
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

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

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

Microorganisms

and other

detritivores

Detritus

Primary producers

Primary consumers

Secondary

consumers

Tertiary

consumers

Heat

Sun

Key

Chemical cycling

Energy 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

Tertiary

consumers

Secondary

consumers

Primary

consumers

Primary

producers

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

Secondary

consumers

Primary

consumers

Primary

producers

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings


In biological magnification


Toxins concentrate at higher trophic levels
because at these levels biomass tends to be lower

Figure 54.23

Concentration of PCBs

Herring

gull eggs

124 ppm

Zooplankton

0.123 ppm

Phytoplankton

0.025 ppm

Lake trout

4.83 ppm

Smelt

1.04 ppm