Chapter 6 How Cells Release Energy Scuba diver

Chapter 6 How Cells Release Energy Scuba diver: © Three Images/Lifesize/Getty Images Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Cells Use Energy in Food to Make ATP Every organism requires a steady food supply to survive. Section 6. 1 Bluebird: © Getty Images/Purestock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Cells Use Energy in Food to Make ATP The bird eats the caterpillar, the caterpillar ate the tree’s leaves, and the tree makes its own food by photosynthesis. Section 6. 1 Bluebird: © Getty Images/Purestock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Cells Use Energy in Food to Make ATP All plants and animals, as well as many microbes, use food (such as glucose) and oxygen gas to produce ATP, an energy carrier used to power cell activities. Section 6. 1 Bluebird: © Getty Images/Purestock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Cells Use Energy in Food to Make ATP The process of using glucose and oxygen to produce ATP is called aerobic respiration. C 6 H 12 O 6 + 6 O 2 (Glucose) Section 6. 1 6 CO 2 + 6 H 2 O + 36 ATP Bluebird: © Getty Images/Purestock (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Cellular Respiration Is Linked to Breathing Inhaled oxygen is consumed in cellular respiration. Carbon dioxide, produced as a byproduct, is then exhaled. Section 6. 1 Mitochondrion: © Thomas Deerinck, NCMIR/SPL/Photo Researchers Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 1

Cellular Respiration Is Linked to Breathing The cell uses the ATP formed during cellular respiration to do work, such as muscle contraction. Section 6. 1 Mitochondrion: © Thomas Deerinck, NCMIR/SPL/Photo Researchers Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 1

Clicker Question #1 Do plants carry out cellular respiration? A. No, photosynthesis has the same function in plants as respiration has in animals and microbes. B. No, their energy needs are too small to require respiration. C. Yes, they require ATP like other living things, and respiration generates ATP. D. Yes, they require cellular respiration as a way to get rid of extra CO 2. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

6. 1 Mastering Concepts How is cellular respiration related to breathing? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Cellular Respiration Occurs in Three Stages ATP synthesis requires energy input. Cellular respiration releases energy from glucose in several steps. Section 6. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 2

Cellular Respiration Occurs in Three Stages During glycolysis, glucose is split into two three-carbon molecules of pyruvate. Section 6. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 2

Cellular Respiration Occurs in Three Stages The pyruvate molecules then enter a mitochondrion, where they are disassembled into carbon dioxide molecules during the Krebs cycle. Section 6. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 2

Cellular Respiration Occurs in Three Stages Glycolysis and the Krebs cycle transfer some of the potential energy in glucose to ATP. Meanwhile, electrons are transferred to NADH and FADH 2. Section 6. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 2

Cellular Respiration Occurs in Three Stages NADH and FADH 2 unload electrons at the electron transport chain, where the potential energy in the electrons is used to produce more ATP. Section 6. 2 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 2

Clicker Question #2 What happens to glucose’s carbon atoms during the overall process of aerobic respiration? A. They are donated to O 2. B. They remain in the pyruvate molecules. C. They become part of ATP. D. They are released as CO 2. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

6. 2 Mastering Concepts What occurs in each of the three stages of cellular respiration? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Mitochondria Produce Most ATP Many of the reactions of cellular respiration occur in mitochondria. Section 6. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 3

Mitochondria Produce Most ATP Mitochondria have two phospholipid bilayers: an outer membrane and an inner membrane. Section 6. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 3

Mitochondria Produce Most ATP Many enzymes span the inner membrane, catalyzing the reactions of the electron transport chain. Section 6. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 3

Mitochondria Produce Most ATP Between the mitochondrial membranes is an intermembrane compartment. Section 6. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 3

Mitochondria Produce Most ATP The space within the inner membrane is the mitochondrial matrix, which houses the reactions of the Krebs cycle. Section 6. 3 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 3

Clicker Question #3 Where is the mitochondrial matrix? A. outside the outer membrane B. between the inner and outer membranes C. inside the inner membrane © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

6. 3 Mastering Concepts Which respiratory reactions occur in each part of the mitochondrion? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Glycolysis Splits Glucose Glycolysis occurs outside of the mitochondrion, in the cytoplasm. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose During glycolysis, a glucose molecule is split into two three-carbon pyruvate molecules. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose The enzymes of glycolysis extract some of the potential energy stored in glucose. The process yields two ATP molecules and two electron-carrying NADH molecules. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose Glycolysis requires an input of two ATP to “activate” glucose. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose The activated glucose is then split into two 3 -carbon molecules. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose Each of the 3 -carbon molecules proceeds to the energy extraction reactions of glycolysis. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose First, each 3 -carbon molecule is oxidized, producing two NADH molecules. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose Then, each 3 -carbon molecule donates its phosphate groups to ADP molecules, producing ATP molecules. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose In total, four ATP are produced. Recall that two ATP were used to start the reactions. The net yield is two ATP. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose Note that these reactions do not require oxygen. Glycolysis can therefore occur in anaerobic conditions. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Glycolysis Splits Glucose Glycolysis yields two ATP molecules, two electron-carrying NADH molecules, and two pyruvates. Section 6. 4 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 4

Clicker Question #4 If 8 glucose molecules enter glycolysis, the net products will be ____ pyruvate molecules and ____ ATP molecules. A. 2 … 2 B. 4 … 4 C. 8 … 8 D. 16 … 16 © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

6. 4 Mastering Concepts What are the starting materials and end products of glycolysis? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Aerobic Respiration Yields Many ATP The reactions of Krebs cycle and the electron transport chain require oxygen gas. These reactions yield much more ATP than glycolysis. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 5

Aerobic Respiration Yields Many ATP The two pyruvate molecules produced in glycolysis undergo an oxidation reaction as they enter the mitochondrion. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 5

Aerobic Respiration Yields Many ATP A carbon atom is stripped from each pyruvate, and leaves the cell as a carbon dioxide molecule. At the same time, NAD+ is reduced to NADH. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 5

Aerobic Respiration Yields Many ATP Through this process, each pyruvate molecule is converted to an acetyl Co. A molecule. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 5

Aerobic Respiration Yields Many ATP Each acetyl Co. A molecule then enters the Krebs cycle. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 5

Aerobic Respiration Yields Many ATP During the Krebs cycle, the two acetyl Co. A molecules are oxidized, yielding 4 CO 2, 2 ATP, 6 NADH, and 2 FADH 2. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 5

Aerobic Respiration Yields Many ATP The Krebs cycle occurs in several steps. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 6

Aerobic Respiration Yields Many ATP Acetyl Co. A combines with a 4 -carbon molecule, yielding citrate. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 6

Aerobic Respiration Yields Many ATP Citrate is then rearranged and oxidized, yielding 3 NADH, 1 FADH 2, and 1 ATP per turn. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 6

Aerobic Respiration Yields Many ATP The original four-carbon molecule is re-created, and the cycle starts anew. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 6

Aerobic Respiration Yields Many ATP Keep in mind that 2 acetyl Co. A molecules are produced from each glucose. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 6

Aerobic Respiration Yields Many ATP Glycolysis Acetyl Co. A formation Krebs cycle So far, aerobic respiration of one glucose molecule has yielded only four ATP. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Aerobic Respiration Yields Many ATP Glycolysis Acetyl Co. A formation Krebs cycle But 10 NADH molecules have been produced, as well as two FADH 2. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Aerobic Respiration Yields Many ATP Glycolysis Acetyl Co. A formation Krebs cycle What happens with all of these electron carrier molecules? Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Aerobic Respiration Yields Many ATP NADH and FADH 2 donate their electrons to the electron transport chain, where energy from the electrons is used to produce many ATP. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 7

Aerobic Respiration Yields Many ATP As electrons travel through the transport chain, carrier molecules use the potential energy of the electrons to transport hydrogen ions into the intermembrane compartment. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 7

Aerobic Respiration Yields Many ATP At the end of the transport chain, electrons are donated to an oxygen atom, which combines with hydrogens to form water. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 7

Aerobic Respiration Yields Many ATP The hydrogen ions move down their concentration gradient from the intermembrane compartment into the matrix through ATP synthase, producing ATP. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 7

Aerobic Respiration Yields Many ATP The electron transport chain produces 34 ATP. Section 6. 5 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 7

6. 5 Mastering Concepts How do NADH and FADH 2 power ATP formation? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Cellular Respiration of One Glucose Yields 36 ATP Glycolysis and Krebs cycle each produce 2 ATP, and the electron transport chain produces 34 ATP. Transporting NADH into the mitochondrion requires 2 ATP, making the total production of ATP equal to 36. Section 6. 6 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 8

6. 6 Mastering Concepts Explain how to arrive at the estimate that each glucose molecule theoretically yields 36 ATPs. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Other Food Molecules Enter the Energy-Extracting Pathways Proteins and fats are also used as energy sources for the cell. These molecules enter the energy-extracting pathways and produce ATP. Section 6. 7 Avocado: © Digital Vision (RF)/Getty Images Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 9

6. 7 Mastering Concepts At which points do digested polysaccharides, proteins, and fats enter the energy pathways? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Fermentation Generates ATP Only in Glycolysis Organisms produce ATP in the absence of oxygen, as well. Section 6. 8 Champagne: © Brand X Pictures (RF)/Punch. Stock; weightlifter: © Corbis (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 10

Fermentation Generates ATP Only in Glycolysis produces ATP and does not require oxygen. Section 6. 8 Champagne: © Brand X Pictures (RF)/Punch. Stock; weightlifter: © Corbis (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 10

Fermentation Generates ATP Only in Glycolysis However, glycolysis does require NAD+, which is re-created in the electron transport chain of cells undergoing respiration. Section 6. 8 Champagne: © Brand X Pictures (RF)/Punch. Stock; weightlifter: © Corbis (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 10

Fermentation Generates ATP Only in Glycolysis In the absence of oxygen, a cell can re-create NAD+ by another pathway, called fermentation. Section 6. 8 Champagne: © Brand X Pictures (RF)/Punch. Stock; weightlifter: © Corbis (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 10

Fermentation Generates ATP Only in Glycolysis In alcoholic fermentation, NADH reduces pyruvate to ethanol. NAD+ is re-created. Section 6. 8 Champagne: © Brand X Pictures (RF)/Punch. Stock; weightlifter: © Corbis (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 10

Fermentation Generates ATP Only in Glycolysis In lactic acid fermentation, NADH reduces pyruvate to lactic acid. NAD+ is re-created. Section 6. 8 Champagne: © Brand X Pictures (RF)/Punch. Stock; weightlifter: © Corbis (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 10

Fermentation Generates ATP Only in Glycolysis During fermentation, oxidation of a glucose molecule yields only 2 ATP. Section 6. 8 Champagne: © Brand X Pictures (RF)/Punch. Stock; weightlifter: © Corbis (RF) Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 10

Clicker Question #5 What is the main advantage of fermentation over aerobic cellular respiration? A. Fermentation generates ATP even if O 2 is not present. B. Fermentation generates more ATP per glucose than aerobic cellular respiration. C. Fermentation does not generate toxic byproducts such as CO 2. D. Fermentation gets rid of pyruvate, which would otherwise accumulate in the cell. © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

6. 8 Mastering Concepts How many ATP molecules per glucose does fermentation produce? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Investigating Life: Plants “Alternative” Lifestyles Yield Hot Sex Philodendron solimoesense plants warm their flowers using an alternative pathway in the electron transport chain. Section 6. 9 Photos: © Marc Gibernau, CNRS Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 11

Investigating Life: Plants “Alternative” Lifestyles Yield Hot Sex The electron transport chain prematurely transfers electrons to O 2. Instead of extracting the remaining potential energy in the electrons, the energy is lost as heat. Section 6. 9 Photos: © Marc Gibernau, CNRS Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 11

Investigating Life: Plants “Alternative” Lifestyles Yield Hot Sex In this case, an inefficient electron transport chain benefits the plant. Beetle pollinators are attracted to the heat. Section 6. 9 Photos: © Marc Gibernau, CNRS Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 11

Investigating Life: Plants “Alternative” Lifestyles Yield Hot Sex Beetles benefit from the heat too. Warm beetles use less energy; the energy they save can be used for finding food or mates. Section 6. 9 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 12

Investigating Life: Plants “Alternative” Lifestyles Yield Hot Sex The hot flowers therefore increase the reproductive success of both the beetles and the plant. Section 6. 9 Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display. Figure 6. 12

6. 9 Mastering Concepts Suppose you hold one group of active beetles at 20°C and another group at 30°C. After several hours, you measure how far each animal can fly at 20°C. Which group should fly farther? © 1996 Photo. Disc, Inc. /Getty Images/RF Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.