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Chapter 7Pathways of

Cellular Respiration

Glucose Breakdown Releases Energy

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7.1 Cellular respiration is a redox reaction that requires O2

Oxidation of substrates, such as glucose, is a fundamental part of cellular respiration

NAD+ and FAD coenzymes assist in oxidation during cellular respiration carrying high-energy electrons to the electron transport chain

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Figure 7.1 Cellular respiration produces ATP

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7.2 Cellular respiration has four phases—three phases occur in mitochondria

Four phases of cellular respiration Glycolysis - an anaerobic process occurs outside

the mitochondria Preparatory (prep) reaction - in the matrix of the

mitochondria pyruvate is broken down to a 2-carbon acetyl group

Citric acid cycle - in the matrix of the mitochondria NADH and FADH2 produced

Electron Transport Chain (ETC) - NADH and FADH2 give up electrons to the chain and energy is released to produce ATP

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Figure 7.2 The four phases of complete glucose breakdown

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Carbon Dioxide and Water Are Produced During

Glucose Breakdown

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7.3 Glycolysis: Glucose breakdown begins

Glycolysis takes place outside the mitochondria and glucose is broken into two pyruvates

Inputs and outputs of glycolysis

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Figure 7.3A Glycolysis

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Figure 7.3B Substrate-level ATP synthesis

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7.4 The preparatory reaction occurs before the citric acid cycle Preparatory (prep) reaction occurs before the

citric acid cycle 3-carbon pyruvate is converted to a 2-carbon

acetyl group and CO2 is given off

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Figure 7.4 Mitochondrion structure

7.5 The citric acid cycle: Final oxidation of glucose products

Citric acid cycle - a cyclic metabolic pathway located in the matrix of mitochondria It produces a lot of the NADH and all of the FADH2

that carry electrons to the electron transport chain

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Figure 7.5 The citric acid cycle

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7.6 The electron transport chain captures much energy

Electron transport chain (ETC) located in the cristae of the mitochondria is a series of carriers that pass electrons Many of the carriers are cytochrome molecules, a

protein that has a tightly bound heme group with a central atom of iron

NADH and FADH2 are recycled to pick up more electrons to bring back to the electron transport chain

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Figure 7.6 The electron transport chain

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7.7 The cristae create an H+ gradient that drives

ATP production

Chemiosmosis As hydrogen ions flow from high to low

concentration ATP synthase synthesizes ATP from ADP + P

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Figure 7.7 Organization and function of cristae

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7.8 The ATP payoff can be calculated

Figure 7.8 Energy yield per glucose molecule 7-19

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Fermentation Is Inefficient

7.9 When oxygen is in short supply, the cell switches to fermentation

Fermentation produces a limited amount of ATP using organic molecules instead of oxygen as the final electron acceptor Benefit of Fermentation

Provide a rapid burst of ATP without oxygen

Drawback of Fermentation Creates oxygen debt Yields 2 ATP, cellular respiration yields ≥36ATP

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Figure 7.9A Fermentation

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

7.10 Fermentation helps produce numerous food products

Fermenting yeasts leaven bread and produce alcohol

Fermenting bacteria produce acids used to make yogurt, sour cream, and cheese

Soy sauce is made by adding a mold and a combination of yeasts and fermenting bacteria to soybeans and wheat

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Metabolic Pathways Cross at Particular Substrates

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7.11 Organic molecules can be broken down and synthesized as needed

Metabolic pool - substrates are entry points for degradation or synthesis of larger molecules Catabolism - reactions that break down molecules Anabolism - reactions that synthesize molecules

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Figure 7.11 The metabolic pool concept

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APPLYING THE CONCEPTS—HOW BIOLOGY IMPACTS OUR LIVES

7.12 Exercise burns fat

Prolonged aerobic exercise burns fat Breathing and heart rate increase during

exercise in order to supply the muscles with adequate oxygen

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Figure 7.12A Sources of fuel for exercise

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Connecting the Concepts:Chapter 7

Energy released when carbohydrates are oxidized and used to produce ATP molecules

Removal of hydrogen atoms occurs during glycolysis, the prep reaction, and the citric acid cycle NADH and FADH2 carry electrons to the electron

transport chain (ETC) to produce ATP Oxygen serves as the final acceptor of electrons, and

water is produced

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