Lecture

Chapter 6 Cellular Respiration: Obtaining Energy from Food

PowerPoint® Lectures for Campbell Essential Biology, Fifth Edition, and Campbell Essential Biology with Physiology, Fourth Edition – Eric J. Simon, Jean L. Dickey, and Jane B. Reece

Lectures by Edward J. Zalisko

© 2013 Pearson Education, Inc.

Biology and Society: Marathoners versus Sprinters • Sprinters do not usually compete at short and long distances. • Natural differences in the muscles of these athletes favor sprinting or long-distance running.


Figure 6.0

Biology and Society: Marathoners versus Sprinters • The muscles that move our legs contain two main types of muscle fibers: 1. slow-twitch and 2. fast-twitch.


Biology and Society: Marathoners versus Sprinters • Slow-twitch fibers – last longer, – do not generate a lot of quick power, and – generate ATP using oxygen (aerobically).


Biology and Society: Marathoners versus Sprinters • Fast-twitch fibers – contract more quickly and powerfully, – fatigue more quickly, and

– can generate ATP without using oxygen (anaerobically).

• All human muscles contain both types of fibers but in different ratios.


ENERGY FLOW AND CHEMICAL CYCLING IN THE BIOSPHERE • Animals depend on plants to convert the energy of sunlight to – chemical energy of sugars and – other organic molecules we consume as food.

• Photosynthesis uses light energy from the sun to – power a chemical process and – make organic molecules.


Producers and Consumers • Plants and other autotrophs (self-feeders) – make their own organic matter from inorganic nutrients.

• Heterotrophs (other-feeders) – include humans and other animals that cannot make organic molecules from inorganic ones.


Producers and Consumers • Autotrophs are producers because ecosystems depend upon them for food. • Heterotrophs are consumers because they eat plants or other animals.


Figure 6.1

Chemical Cycling between Photosynthesis and Cellular Respiration • The ingredients for photosynthesis are carbon dioxide (CO2) and water (H2O). – CO2 is obtained from the air by a plant’s leaves. – H2O is obtained from the damp soil by a plant’s roots.


Chemical Cycling between Photosynthesis and Cellular Respiration • Chloroplasts in the cells of leaves use light energy to rearrange the atoms of CO2 and H2O, which produces – sugars (such as glucose), – other organic molecules, and – oxygen gas.


Figure 6.UN07

C6H12O6

 6

O2

6

CO2

 6 H2O  Approx. 32

ATP

Chemical Cycling between Photosynthesis and Cellular Respiration • Plant and animal cells perform cellular respiration, a chemical process that – primarily occurs in mitochondria,

– harvests energy stored in organic molecules, – uses oxygen, and – generates ATP.


Chemical Cycling between Photosynthesis and Cellular Respiration • The waste products of cellular respiration are – CO2 and H2O, – used in photosynthesis.


Chemical Cycling between Photosynthesis and Cellular Respiration • Animals perform only cellular respiration. • Plants perform – photosynthesis and – cellular respiration.


Chemical Cycling between Photosynthesis and Cellular Respiration • Plants usually make more organic molecules than they need for fuel. This surplus provides material that can be – used for the plant to grow or – stored as starch in potatoes.


Figure 6.2

Sunlight energy enters ecosystem

Photosynthesis C6H12O6

CO2

O2

H2O

Cellular respiration

ATP

drives cellular work Heat energy exits ecosystem

Figure 6.UN06

Heat

C6H12O6 Sunlight

O2 ATP Cellular respiration

Photosynthesis

CO2

H2O

CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY • Cellular respiration is – the main way that chemical energy is harvested from food and converted to ATP and – an aerobic process—it requires oxygen.


CELLULAR RESPIRATION: AEROBIC HARVEST OF FOOD ENERGY • Cellular respiration and breathing are closely related. – Cellular respiration requires a cell to exchange gases with its surroundings. – Cells take in oxygen gas. – Cells release waste carbon dioxide gas.

– Breathing exchanges these same gases between the blood and outside air.


Figure 6.3

O2

CO2

Breathing Lungs

O2

CO2

Cellular respiration

Muscle cells

The Simplified Equation for Cellular Respiration • A common fuel molecule for cellular respiration is glucose. • Cellular respiration can produce up to 32 ATP molecules for each glucose molecule consumed. • The overall equation for what happens to glucose during cellular respiration is – glucose & oxygen  CO2, H2O, & a release of energy.


Figure 6.UN01

C6H12O6 Glucose

6

O2 Oxygen

6

CO2

Carbon dioxide

6

H2O

ATP

Water

Energy

The Role of Oxygen in Cellular Respiration • During cellular respiration, hydrogen and its bonding electrons change partners from sugar to oxygen, forming water as a product.


Redox Reactions • Chemical reactions that transfer electrons from one substance to another are called – oxidation-reduction reactions or – redox reactions for short.


Redox Reactions • The loss of electrons during a redox reaction is oxidation. • The acceptance of electrons during a redox reaction is reduction.

• During cellular respiration – glucose is oxidized and – oxygen is reduced.


Figure 6.UN02

Oxidation Glucose loses electrons (and hydrogens)

C6H12O6 Glucose

6

O2

Oxygen

6

CO2 Carbon dioxide

6 H2O Water

Reduction Oxygen gains electrons (and hydrogens)

Redox Reactions • Why does electron transfer to oxygen release energy? – When electrons move from glucose to oxygen, it is as though the electrons were falling. – This ―fall‖ of electrons releases energy during cellular respiration.


Figure 6.4

1 2

H2

Release of heat energy

H 2O

O2

Figure 6.UN08

Oxidation Glucose loses electrons (and hydrogens) CO2

C6H12O6

ATP

Electrons (and hydrogens) O2

H 2O

Reduction Oxygen gains electrons (and hydrogens)

Redox Reactions • Cellular respiration is – a controlled fall of electrons and – a stepwise cascade much like going down a staircase.


NADH and Electron Transport Chains • The path that electrons take on their way down from glucose to oxygen involves many steps. • The first step is an electron acceptor called NAD+. – NAD is made by cells from niacin, a B vitamin. – The transfer of electrons from organic fuel to NAD+ reduces it to NADH.


NADH and Electron Transport Chains • The rest of the path consists of an electron transport chain, which – involves a series of redox reactions and – ultimately leads to the production of large amounts of ATP.


Figure 6.5

e e

Electrons from food e e NADH

NAD

2 H

Stepwise release of energy used to make ATP

2 e

2 e

2 H Hydrogen, electrons, and oxygen combine to produce water

1 2

H2O

O2

Figure 6.5a

2 H

ATP

2 e

Stepwise release of energy used to make ATP

Electron transport chain

2 e 2 H Hydrogen, electrons, and oxygen combine to produce water

1 2

H2O

O2

An Overview of Cellular Respiration • Cellular respiration is an example of a metabolic pathway, which is a series of chemical reactions in cells.

• All of the reactions involved in cellular respiration can be grouped into three main stages: 1. glycolysis, 2. the citric acid cycle, and 3. electron transport.


Figure 6.6

Mitochondrion

Cytoplasm

Cytoplasm

Animal cell

Plant cell

Cytoplasm

Mitochondrion High-energy electrons via carrier molecules

Glycolysis

2 Pyruvic acid

Glucose

ATP

Citric Acid Cycle

ATP

Electron Transport

ATP

The Three Stages of Cellular Respiration • With the big-picture view of cellular respiration in mind, let’s examine the process in more detail.


Stage 1: Glycolysis 1. A six-carbon glucose molecule is split in half to form two molecules of pyruvic acid. 2. These two molecules then donate high energy electrons to NAD+, forming NADH.


Figure 6.7 OUTPUT

INPUT – – NADH P

2 ATP

P

NAD

P

2 ATP

2 ADP 2

3

2 ADP

P 2 Pyruvic acid

1 P

P P

2

3

Glucose NAD

Energy investment phase Key Carbon atom P Phosphate group – High-energy electron

2 ADP – – NADH

P

2 ATP

Energy harvest phase

Figure 6.7a

INPUT

OUTPUT

2 Pyruvic acid

Glucose

Stage 1: Glycolysis 3. _________ 3. Glycolysis – ____ ___ _________ ___ _______ __ _____ ___ ___ ______ _______ – ___ uses two ATP molecules per glucose to split the

six-carbon glucose and

– _____ ____ __________ ________ ____ _______ ________ ______ ____ ____ _________ __ – _________ makes four additional ATP directly when enzymes

phosphate fuel molecules to • ___ transfer __________ ________groups _ ___ __from ___ _________ __ ___ ADP. _______ ________

• Thus, glycolysis produces a net of two molecules of ATP per glucose molecule.


Figure 6.8

Enzyme

P

P

ADP

ATP

P

Stage 2: The Citric Acid Cycle • In the citric acid cycle, pyruvic acid from glycolysis is first ―groomed.‖ – Each pyruvic acid loses a carbon as CO2.

– The remaining fuel molecule, with only two carbons left, is acetic acid.

• Oxidation of the fuel generates NADH.


Stage 2: The Citric Acid Cycle • Finally, each acetic acid is attached to a molecule called coenzyme A to form acetyl CoA. • The CoA escorts the acetic acid into the first reaction of the citric acid cycle. • The CoA is then stripped and recycled.


Figure 6.9

INPUT

OUTPUT 2 Oxidation of the fuel generates NADH – – NADH NAD

(from glycolysis)

(to citric acid cycle) CoA

Pyruvic acid

1 Pyruvic acid loses a carbon as CO2

Acetic acid

CO2

Coenzyme A

3 Acetic acid attaches to coenzyme A

Acetyl CoA

Figure 6.9a

INPUT

OUTPUT

(from glycolysis)

(to citric acid cycle) CoA

Pyruvic acid

Acetyl CoA

Stage 2: The Citric Acid Cycle • The citric acid cycle – extracts the energy of sugar by breaking the acetic acid molecules all the way down to CO2,

– uses some of this energy to make ATP, and – forms NADH and FADH2.


Figure 6.10

INPUT

OUTPUT

Citric acid

1 Acetic acid

2 CO2

ADP  P

ATP

Citric Acid Cycle 3

NAD

FAD 6 Acceptor molecule

2

3

– – 3 NADH

4

– – FADH2

5

Figure 6.10a

INPUT 1 Acetic acid ADP  P

OUTPUT

2 CO2 ATP

2

3

3 NAD

– – 3 NADH

4

FAD

– – FADH2

5

Stage 3: Electron Transport • Electron transport releases the energy your cells need to make the most of their ATP. • The molecules of the electron transport chain are built into the inner membranes of mitochondria.

• The chain – functions as a chemical machine, which – uses energy released by the ―fall‖ of electrons to pump hydrogen ions across the inner mitochondrial membrane, and – uses these ions to store potential energy.


Stage 3: Electron Transport • When the hydrogen ions flow back through the membrane, they release energy. – The hydrogen ions flow through ATP synthase.

– ATP synthase – takes the energy from this flow and

– synthesizes ATP.


Figure 6.11

H

Space between membranes

H

H

H

H

H



H

Electron carrier

H

H

H



H

H

3

5

H

Protein complex Inner mitochondrial membrane

–

–

FADH2

Electron flow

FAD

H

2 –

1 2

–

1

H

2

H

H2O

6

4

NAD

NADH

O2

ADP

H

H

ATP

P

H

H

Matrix


ATP synthase

Figure 6.11a


H H

H

H

H

Electron carrier

H



H

H

H

H H

3

H

5

H


–

–

FADH2

Electron flow

FAD

H

2 –

1 2

–

1

H

 2 H

H2O

6

4

NAD

NADH

O2

ADP H

H

ATP

P H

H

Matrix


ATP synthase

Figure 6.11b


H H

Electron carrier

H

H

H H

H

H

H

H H

3


–

–

FADH2

Electron flow

FAD

H

2 –

1 2

–

1

4



NADH

NAD H

H

H

Matrix

O2


H

2 H

Figure 6.11c

H H



H

H H

5

1 2

O2

2 H

H

6

H2O

4 ADP H

ATP

P H

ATP synthase

Stage 3: Electron Transport • Cyanide is a deadly poison that – binds to one of the protein complexes in the electron transport chain,

– prevents the passage of electrons to oxygen, and – stops the production of ATP.


The Results of Cellular Respiration • Cellular respiration can generate up to 32 molecules of ATP per molecule of glucose.


Figure 6.12

Cytoplasm Mitochondrion – 2

–

–

NADH

2

–

NADH

6

–

2 Glycolysis Glucose

2 Pyruvic acid

2 ATP by direct synthesis

2 Acetyl CoA

– – NADH –

FADH2

Citric Acid Cycle

Electron Transport

2 ATP

About 28 ATP

by direct synthesis

Maximum per glucose:

by ATP synthase

About 32 ATP

Figure 6.12a

Glycolysis

2 Pyruvic acid

2 Acetyl CoA

Citric Acid Cycle

Electron Transport

2 ATP

2 ATP

About 28 ATP

by direct synthesis

by direct synthesis

Glucose

by ATP synthase

The Results of Cellular Respiration • In addition to glucose, cellular respiration can ―burn‖ – diverse types of carbohydrates,

– fats, and – proteins.


Figure 6.13

Food

Polysaccharides

Fats

Proteins

Sugars

Fatty acids

Amino acids

Glycerol

Glycolysis

Acetyl CoA

Citric Acid Cycle

Electron Transport

ATP

FERMENTATION: ANAEROBIC HARVEST OF FOOD ENERGY • Some of your cells can actually work for short periods without oxygen. • Fermentation is the anaerobic (without oxygen) harvest of food energy.


Fermentation in Human Muscle Cells • After functioning anaerobically for about 15 seconds, muscle cells begin to generate ATP by the process of fermentation.

• Fermentation relies on glycolysis to produce ATP. • Glycolysis – does not require oxygen and – produces two ATP molecules for each glucose broken down to pyruvic acid.


Fermentation in Human Muscle Cells • Pyruvic acid, produced by glycolysis, – is reduced by NADH, – producing NAD+, which – keeps glycolysis going.

• In human muscle cells, lactic acid is a by-product.


Fermentation Overview © 2013 Pearson Education, Inc.

Figure 6.14

INPUT

OUTPUT 2 ADP 2 P

2 ATP

Glycolysis

2 NAD

– – 2 NADH

– – 2 NADH 2 Pyruvic acid

Glucose

2 H

2 NAD

2 Lactic acid

The Process of Science: What Causes Muscle Burn? • Observation: Muscles produce lactic acid under anaerobic conditions.

• Question: Does the buildup of lactic acid cause muscle fatigue?


The Process of Science: What Causes Muscle Burn? • Hypothesis: The buildup of lactic acid would cause muscle activity to stop.

• Experiment: Tested frog muscles under conditions when lactic acid – could and – could not diffuse away.


Figure 6.15

Battery

Battery 

–



Force measured

–

Force measured

Frog muscle stimulated by electric current

Solution prevents diffusion of lactic acid

Solution allows diffusion of lactic acid; muscle can work for twice as long

The Process of Science: What Causes Muscle Burn? • Results: When lactic acid could diffuse away, performance improved greatly.

• Conclusion: Lactic acid accumulation is the primary cause of failure in muscle tissue. • However, recent evidence suggests that the role of lactic acid in muscle function remains unclear.


Fermentation in Microorganisms • Fermentation alone is able to sustain many types of microorganisms. • The lactic acid produced by microbes using fermentation is used to produce – cheese, sour cream, and yogurt,

– soy sauce, pickles, and olives, and – sausage meat products.


Fermentation in Microorganisms • Yeast is a microscopic fungus that – uses a different type of fermentation and – produces CO2 and ethyl alcohol instead of lactic acid.

• This type of fermentation, called alcoholic fermentation, is used to produce – beer, – wine, and – breads.


Figure 6.16

INPUT

OUTPUT 2 ADP 2 P

2 ATP 2 CO2 released

Glycolysis

2 NAD Glucose

–

–

–

2 NADH

–

2 NADH 2 Pyruvic acid

 2 H

2 NAD

2 Ethyl alcohol

Figure 6.UN09

Mitochondrion O2

– 2

–

–

NADH

2

–

6

NADH 2

Glycolysis Glucose

2 Acetyl CoA

2 Pyruvic acid

– – NADH – – FADH2

Citric Acid Cycle

2 CO2 2 ATP

by direct synthesis

Electron Transport

4 CO2

by direct synthesis

2 ATP

About 32 ATP

H2O About 28 ATP

by ATP synthase

Evolution Connection: Life before and after Oxygen • Glycolysis could be used by ancient bacteria to make ATP – when little oxygen was available, and – before organelles evolved.

• Today, glycolysis – occurs in almost all organisms and

– is a metabolic heirloom of the first stage in the breakdown of organic molecules. © 2013 Pearson Education, Inc.

Figure 6.17

2.1 2.2 2.7

O2 present in Earth’s atmosphere

Billions of years ago

0

First eukaryotic organisms Atmospheric oxygen reaches 10% of modern levels Atmospheric oxygen first appears

3.5

Oldest prokaryotic fossils

4.5

Origin of Earth

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