Download BIO121_Chapter 6

3/24/2014
CHAPTER 6: How Cells
Release Energy
BIO 121
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
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
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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
Cells Use Energy in Food to Make ATP
The process of using glucose and oxygen to produce ATP is called aerobic respiration.
C6H12O6 + 6O2
6CO2 + 6H2O + 36ATP
(Glucose)
Section 6.1
Bluebird: © Getty Images/Purestock RF
Cellular respiration is
the set of the
metabolic reactions
and processes that
take place in the cells
of organisms to
convert biochemical
energy from nutrients
into adenosine
triphosphate (ATP),
and then release
waste products.
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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/Science Source
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/Science Source
Figure 6.1
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 CO2.
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ANSWER
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 CO2.
Cellular Respiration Occurs in Three Stages
ATP synthesis requires energy input. Cellular respiration releases energy from glucose in several steps.
Section 6.2
Figure 6.2
Cellular Respiration Occurs in Three Stages
During glycolysis, glucose is split into two three‐carbon molecules of pyruvate.
Section 6.2
Figure 6.2
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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
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 FADH2. Section 6.2
Figure 6.2
Cellular Respiration Occurs in Three Stages
NADH and FADH2 unload electrons at the electron transport chain, where the potential energy in the electrons is used to produce more ATP. Section 6.2
Figure 6.2
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Question #2
What happens to glucose’s carbon atoms during the overall process of aerobic respiration?
A. They are donated to O2.
B. They remain in the pyruvate molecules.
C. They become part of ATP.
D. They are released as CO2.
ANSWER
What happens to glucose’s carbon atoms during the overall process of aerobic respiration?
A. They are donated to O2.
B. They remain in the pyruvate molecules.
C. They become part of ATP.
D. They are released as CO2.
Flower: © Doug Sherman/Geofile/RF
Mitochondria Produce Most ATP
Many of the reactions of cellular respiration occur in mitochondria. Section 6.3
Figure 6.3
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Mitochondria Produce Most ATP
Mitochondria have two phospholipid bilayers: an outer membrane and an inner membrane. Section 6.3
Figure 6.3
Mitochondria Produce Most ATP
Many enzymes span the inner membrane, catalyzing the reactions of the electron transport chain.
Section 6.3
Figure 6.3
Mitochondria Produce Most ATP
Between the mitochondrial membranes is an intermembrane compartment.
Section 6.3
Figure 6.3
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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
Figure 6.3
Question #3
Where is the mitochondrial matrix?
A. Outside the outer membrane
B. Between the inner and outer membranes
C. Inside the inner membrane
ANSWER
Where is the mitochondrial matrix?
A. Outside the outer membrane
B. Between the inner and outer membranes
C. Inside the inner membrane
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Glycolysis Splits Glucose
Glycolysis occurs outside of the mitochondrion, in the cytoplasm. Section 6.4
Figure 6.4
Glycolysis Splits Glucose
During glycolysis, a glucose molecule is split into two three‐carbon pyruvate molecules. Section 6.4
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
Figure 6.4
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Glycolysis Splits Glucose
Glycolysis requires an input of two ATP to “activate” glucose.
Section 6.4
Figure 6.4
Glycolysis Splits Glucose
The activated glucose is then split into two 3‐carbon molecules.
Section 6.4
Figure 6.4
Glycolysis Splits Glucose
Each of the 3‐carbon molecules proceeds to the energy extraction reactions of glycolysis.
Section 6.4
Figure 6.4
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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
Figure 6.4
Glycolysis Splits Glucose
Note that these reactions do not require oxygen. Glycolysis can therefore occur in anaerobic conditions. Section 6.4
Figure 6.4
Glycolysis Splits Glucose
Glycolysis yields two ATP molecules, two electron‐carrying NADH molecules, and two pyruvates.
Section 6.4
Figure 6.4
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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
ANSWER
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
6.4 Mastering Concepts
What are the starting materials and end products of glycolysis? Snake © Gunter Ziesler/Photoshot
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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
Aerobic Respiration Yields Many ATP
The two pyruvate molecules produced in glycolysis undergo an oxidation reaction as they enter the mitochondrion (this is sometimes called the transition step).
Section 6.5
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
Figure 6.5
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Aerobic Respiration Yields Many ATP
Through this process, each pyruvate molecule is converted to an acetyl CoA molecule.
Section 6.5
Figure 6.5
Aerobic Respiration Yields Many ATP
Each acetyl CoA molecule then enters the Krebs cycle.
Section 6.5
Figure 6.5
Aerobic Respiration Yields Many ATP
During the Krebs cycle, the two acetyl CoA molecules are oxidized, yielding 4 CO2, 2 ATP, 6 NADH, and 2 FADH2. Section 6.5
Figure 6.5
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Aerobic Respiration Yields Many ATP
The Krebs cycle occurs in several steps. Section 6.5
Figure 6.6
Aerobic Respiration Yields Many ATP
Glycolysis
Acetyl CoA formation
Krebs cycle
So far, aerobic respiration of one glucose molecule has yielded only four ATP. Section 6.5
Aerobic Respiration Yields Many ATP
Glycolysis
Acetyl CoA formation
Krebs cycle
But 10 NADH molecules have been produced, as well as two FADH2.
Section 6.5
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Aerobic Respiration Yields Many ATP
Glycolysis
Acetyl CoA formation
Krebs cycle
What happens with all of these electron carrier molecules? Section 6.5
Aerobic Respiration Yields Many ATP
NADH and FADH2 donate their electrons to the electron transport chain, where energy from the electrons is used to produce many ATP.
Section 6.5
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
Figure 6.7
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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
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.
Section 6.5
Figure 6.7
Aerobic Respiration Yields Many ATP
ATP synthase produces ATP via chemiosmotic phosphorylation.
Section 6.5
Figure 6.7
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Aerobic Respiration Yields Many ATP
The electron transport chain produces 34 ATP.
Section 6.5
Figure 6.7
Cellular Respiration of One Glucose Yields 36 ATP
Glycolysis
Acetyl CoA formation
Krebs cycle
Electron transport 34
Section 6.5
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
Figure 6.8
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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/Getty Images RF
Figure 6.9
Fermentation Generates ATP Only in Glycolysis
Organisms produce ATP in the absence of oxygen, as well. Section 6.8
Figure 6.10
Fermentation Generates ATP Only in Glycolysis
Glycolysis produces ATP and does not require oxygen. Section 6.8
Figure 6.10
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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
Figure 6.10
Fermentation Generates ATP Only in Glycolysis
In the absence of oxygen, a cell can re‐create NAD+ other pathways, called anaerobic respiration and fermentation.
Section 6.8
Figure 6.10
Fermentation Generates ATP Only in Glycolysis
In anaerobic respiration, NADH donates is oxidized at an electron transport chain that uses electron acceptor molecules other than O2. Section 6.8
Figure 6.10
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Fermentation Generates ATP Only in Glycolysis
Fermentation uses pyruvate to oxidize NADH, producing alcohol, lactic acid, or other byproducts. Section 6.8
Figure 6.10
Fermentation Generates ATP Only in Glycolysis
In alcoholic fermentation, NADH reduces pyruvate to ethanol. NAD+ is re‐created. Section 6.8
Beer: © Adam Woolfitt/Corbis; Yogurt: © Scimat/Science Source
Figure 6.11
Fermentation Generates ATP Only in Glycolysis
In alcoholic fermentation, NADH reduces pyruvate to ethanol. NAD+ is re‐created. Section 6.8
Beer: © Adam Woolfitt/Corbis; Yogurt: © Scimat/Science Source
In lactic acid fermentation, NADH reduces pyruvate to lactic acid. NAD+ is re‐created. Figure 6.11
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Fermentation Generates ATP Only in Glycolysis
During fermentation, oxidation of a glucose molecule yields only 2 ATP.
Section 6.8
Beer: © Adam Woolfitt/Corbis; Yogurt: © Scimat/Science Source
Figure 6.11
Question #5
What is the main advantage of fermentation over aerobic cellular respiration?
A. Fermentation generates ATP even if O2 is not present.
B. Fermentation generates more ATP per glucose than aerobic cellular respiration.
C. Fermentation does not generate toxic byproducts such as CO2.
D. Fermentation gets rid of pyruvate, which would otherwise accumulate in the cell.
ANSWER
What is the main advantage of fermentation over aerobic cellular respiration?
A. Fermentation generates ATP even if O2 is not present.
B. Fermentation generates more ATP per glucose than aerobic cellular respiration.
C. Fermentation does not generate toxic byproducts such as CO2.
D. Fermentation gets rid of pyruvate, which would otherwise accumulate in the cell.
Flower: © Doug Sherman/Geofile/RF
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Photosynthesis and Respiration Are Ancient Pathways
Photosynthesis and respiration are connected in many ways: water, oxygen, carbon dioxide, sugars.
Section 6.9
Figure 6.12
Photosynthesis and Respiration Are Ancient Pathways
Both of these chemical processes arose in unicellular organisms over 3 billion years ago. Section 6.9
Figure 6.12
Photosynthesis and Respiration Are Ancient Pathways
Since virtually all cells carry out glycolysis, it is probably the first of these energy pathways to arise. Section 6.9
Figure 6.12
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Photosynthesis and Respiration Are Ancient Pathways
Photosynthesis may have evolved from glycolysis, since some Calvin cycle reactions are the reverse of glycolysis reactions.
Section 6.9
Figure 6.12
Photosynthesis and Respiration Are Related
Section 6.9
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