Chapter 6 Introduction How Cells Harvest Chemical Energy

Chapter 6

Introduction

How Cells Harvest Chemical Energy

? In eukaryotes, cellular respiration

¨C harvests energy from food,

¨C yields large amounts of ATP, and

¨C Uses ATP to drive cellular work.

? A similar process takes place in many prokaryotic

organisms.

PowerPoint Lectures for

Campbell Biology: Concepts & Connections, Seventh Edition

Reece, Taylor, Simon, and Dickey

Lecture by Edward J. Zalisko

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? 2012 Pearson Education, Inc.

Figure 6.0_1

Figure 6.0_2

Chapter 6: Big Ideas

Cellular Respiration:

Aerobic Harvesting

of Energy

Fermentation: Anaerobic

Harvesting of Energy

Stages of Cellular

Respiration

Connections Between

Metabolic Pathways

6.1 Photosynthesis and cellular respiration

provide energy for life

CELLULAR RESPIRATION:

AEROBIC HARVESTING

OF ENERGY

? Life requires energy.

? In almost all ecosystems, energy ultimately comes

from the sun.

? In photosynthesis,

¨C some of the energy in sunlight is captured by

chloroplasts,

¨C atoms of carbon dioxide and water are rearranged, and

¨C glucose and oxygen are produced.

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6.1 Photosynthesis and cellular respiration

provide energy for life

Figure 6.1

Sunlight energy

ECOSYSTEM

? In cellular respiration

Photosynthesis

in chloroplasts

¨C glucose is broken down to carbon dioxide and water

and

Glucose

CO2

¨C the cell captures some of the released energy to make

ATP.

O2

H2O

Cellular respiration

in mitochondria

? Cellular respiration takes place in the mitochondria

of eukaryotic cells.

(for cellular

ATP

work)

Heat energy

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Figure 6.1_1

Figure 6.1_2

Sunlight energy

ECOSYSTEM

Photosynthesis

in chloroplasts

Glucose

CO2

O2

H2O

Cellular respiration

in mitochondria

(for cellular

ATP

work)

Heat energy

6.2 Breathing supplies O2 for use in cellular

respiration and removes CO2

Figure 6.2

O2

Breathing

? Respiration, as it relates to breathing, and cellular

respiration are not the same.

¨C Respiration, in the breathing sense, refers to an

exchange of gases. Usually an organism brings in

oxygen from the environment and releases waste CO2.

CO2

Lungs

CO2

Bloodstream

O2

¨C Cellular respiration is the aerobic (oxygen requiring)

harvesting of energy from food molecules by cells.

Muscle cells carrying out

Cellular Respiration

Glucose ? O2

CO2 ? H2O ? ATP

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Figure 6.2_1

Figure 6.2_2

O2

Breathing

CO2

Lungs

CO2

Bloodstream

O2

Muscle cells carrying out

Cellular Respiration

Glucose ? O2

CO2 ? H2O ? ATP

6.3 Cellular respiration banks energy in ATP

molecules

Figure 6.3

? Cellular respiration is an exergonic process that

transfers energy from the bonds in glucose to form

ATP.

? Cellular respiration

¨C produces up to 32 ATP molecules from each glucose

molecule and

C6H12O6

6

Glucose

Oxygen

O2

6 CO2

Carbon

dioxide

6

H2O

ATP

Water

? Heat

¨C captures only about 34% of the energy originally stored

in glucose.

? Other foods (organic molecules) can also be used

as a source of energy.

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6.4 CONNECTION: The human body uses energy

from ATP for all its activities

6.4 CONNECTION: The human body uses energy

from ATP for all its activities

? The average adult human needs about 2,200 kcal

of energy per day.

? A kilocalorie (kcal) is

¨C About 75% of these calories are used to maintain a

healthy body.

¨C The remaining 25% is used to power physical activities.

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¨C the quantity of heat required to raise the temperature of

1 kilogram (kg) of water by 1oC,

¨C the same as a food Calorie, and

¨C used to measure the nutritional values indicated on food

labels.

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Figure 6.4

Figure 6.4_1

Activity

Running (8¨C9 mph)

979

Dancing (fast)

510

Bicycling (10 mph)

408

Walking (4 mph)

341

Walking (3 mph)

245

Dancing (slow)

Sitting (writing)

kcal consumed per hour

by a 67.5-kg (150-lb) person*

Running (8¨C9 mph)

979

Dancing (fast)

510

490

Swimming (2 mph)

Driving a car

Activity

kcal consumed per hour

by a 67.5-kg (150-lb) person*

204

61

28

*Not including kcal needed for

body maintenance

Bicycling (10 mph)

490

Swimming (2 mph)

408

Walking (4 mph)

341

Walking (3 mph)

245

Dancing (slow)

Driving a car

Sitting (writing)

204

61

28

*Not including kcal needed for

body maintenance

Figure 6.4_2

6.5 Cells tap energy from electrons ¡°falling¡±

from organic fuels to oxygen

? The energy necessary for life is contained in the

arrangement of electrons in chemical bonds in

organic molecules.

? An important question is how do cells extract this

energy?

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6.5 Cells tap energy from electrons ¡°falling¡±

from organic fuels to oxygen

6.5 Cells tap energy from electrons ¡°falling¡±

from organic fuels to oxygen

? When the carbon-hydrogen bonds of glucose are

broken, electrons are transferred to oxygen.

? Energy can be released from glucose by simply

burning it.

¨C Oxygen has a strong tendency to attract electrons.

? The energy is dissipated as heat and light and is

not available to living organisms.

¨C An electron loses potential energy when it ¡°falls¡± to

oxygen.

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6.5 Cells tap energy from electrons ¡°falling¡±

from organic fuels to oxygen

6.5 Cells tap energy from electrons ¡°falling¡±

from organic fuels to oxygen

? On the other hand, cellular respiration is the

controlled breakdown of organic molecules.

? The movement of electrons from one molecule to

another is an oxidation-reduction reaction, or

redox reaction. In a redox reaction,

? Energy is

¨C gradually released in small amounts,

¨C captured by a biological system, and

¨C stored in ATP.

¨C the loss of electrons from one substance is called

oxidation,

¨C the addition of electrons to another substance is called

reduction,

¨C a molecule is oxidized when it loses one or more

electrons, and

¨C reduced when it gains one or more electrons.

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6.5 Cells tap energy from electrons ¡°falling¡±

from organic fuels to oxygen

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Figure 6.5A

? A cellular respiration equation is helpful to show

the changes in hydrogen atom distribution.

Loss of hydrogen atoms

(becomes oxidized)

? Glucose

¨C loses its hydrogen atoms and

C6H12O6

¨C becomes oxidized to CO2.

Glucose

6 CO2

6 O2

6 H 2O

? Heat

Gain of hydrogen atoms

(becomes reduced)

? Oxygen

ATP

¨C gains hydrogen atoms and

¨C becomes reduced to H2O.

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6.5 Cells tap energy from electrons ¡°falling¡±

from organic fuels to oxygen

Figure 6.5B

? Enzymes are necessary to oxidize glucose and

other foods.

Becomes oxidized

2H

? NAD+

¨C is an important enzyme in oxidizing glucose,

¨C accepts electrons, and

Becomes reduced

NAD?

2H

NADH

¨C becomes reduced to NADH.

2 H?

2

H?

(carries

2 electrons)

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