Download 4.5 Cellular Respiration in Detail

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4.5
Cellular Respiration
in Detail
Teacher Notes and Answers
SECTION 5
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1.4ATP, 2NADH, and 2pyruvate should
be circled.
2.They are energy-carrying molecules that trans-
fer energy to the electron transport chain.
3.chloroplast, mitochondrion
The Big Picture
1.NADH and pyruvate
2.NADH and FADH2
3.carbon dioxide (CO2), as a waste product; water
(H2O), as a waste product; up to 38 ATP
4.They are built up on one side of the membrane,
so they flow through ATP synthase to make
ATP.
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section
4.5
Cellular Respiration
in Detail
Key Concept Cellular respiration is an aerobic process with two main stages.
Glycolysis is needed for cellular respiration.
In Section 4.4 you read a summary of cellular respiration. Now, we will
look at the process more closely, starting with glycolysis. The process of
glycolysis happens in all cells, including yours. It does not require oxygen. If oxygen is available, the products of glycolysis are used in cellular
respiration.
Glycolysis alone produces a small amount of ATP. But other products
of glycolysis are used later in cellular respiration to make lots of ATP.
These other products are NADH, which carries energy, and pyruvate.
NADH is an energy-carrying molecule similar to NADPH in photosynthesis. In cellular respiration, NADH carries energy to an electron transport chain. Pyruvate (py-ROO-vayt) is the three-carbon molecule that is
broken down in the mitochondria during cellular respiration.
2
ATP
C C C C C C
glucose
2
ADP
4
ADP
4
ATP
C C C
C C C
C C C
C C C
2 NAD+
2 NADH
2 pyruvate
Glycolysis breaks glucose into 2 three-carbon molecules
called pyruvate. NADH and ATP are also produced.
Notice that two ATP are used in the process of glycolysis. Four ATP
are made. The net gain is 4 ATP made – 2 ATP used = 2 ATP molecules.
In summary, for each molecule of glucose that is broken down, the products of glycolysis are:
• 2 ATP
• 2 NADH
• 2 pyruvate
The ATP is energy for the cell. The NADH and pyruvate are needed
for cellular respiration.
On the chemical formula above, circle the three products of glycolysis: ATP, NADH, and pyruvate.
2
McDougal Littell Biology
The Krebs cycle is the first main part of
cellular respiration.
matrix
Cellular respiration makes many more ATP molecules than does
glycolysis. The process begins with pyruvate entering the mitochondria. Pyruvate then gets broken down. Next, the process continues
with the Krebs cycle. There are many steps in the Krebs cycle, highlighted below.
The Krebs cycle takes place
in the mitochondrion matrix.
The krebs Cycle
NADH
1
NAD+
CoA
C
C C C C C C
3
CO2
NADH
C C
C
citric acid
C C C
4
CO2
NAD+
Pyruvate (from glycolysis)
is broken down.
Citric acid is broken
down and NADH is made.
C C C C C
NAD+
Citric acid is formed.
NADH
Coenzyme A
(CoA)
ATP
C
C C -CoA
2
ADP
C C C C
Coenzyme A bonds to the two-carbon molecule. This
intermediate molecule enters
the Krebs cycle.
C C C C
C C C C
NAD+
NADH
FAD2+
6
5
CO2
The five-carbon molecule is broken
down. NADH and ATP are made.
The four-carbon molecule is rearranged. NADH and FADH2 are formed.
FADH2
The main function of the Krebs cycle is to produce energy-carrying
molecules, such as NADH. Another energy-carrying molecule that the
Krebs cycle produces is called FADH2. These molecules transfer energy to
the electron transport chain, the next main part of cellular respiration.
For each pyruvate, the products of the Krebs cycle are:
• 3 CO2
• 1 ATP
• 4 NADH
• 1 FADH2
Carbon dioxide (CO2) is given off as a waste product. The ATP is
energy for the cell. NADH and FADH2 are energy-carrying molecules
that are used in the next part of cellular respiration.
What are NADH and FADH2 used for in the cell?
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The electron transport chain is the second main
part of cellular respiration.
The electron transport chain in cellular respiration is similar to the
electron transport chain in photosynthesis. Some of the similarities
include:
• Both are made of proteins that are in a membrane. In cellular respiration, the electron transport chain takes place in and across the
inner membrane of a mitochondrion.
• Both move energy along the electron transport chain. In cellular
respiration, energized electrons are provided by NADH and FADH2.
• Both use that energy to pump hydrogen ions (H+) across a
membrane, so that there are more H+ ions on one side of
the membrane than the other.
• In both processes, the H+ ions then flow back through ATP
synthase in the membrane to produce ATP.
inner
membrane
the electron transport chain
H+
2
proteins in the
inner membrane
Hydrogen ions are
transported across
the membrane.
H+
H+
inner membrane
of mitochodrion
e-
e-
NADH
FADH2
1
4
Electrons are
removed from
NADH and FADH2.
H+
H+
H+
e-
e-
H+
The electron transport chain is in
the inner mitochondrial membrane.
H+
H+
H+
matrix
e-
H+
ATP synthase
+P
H+
ADP
NAD+
FAD2+
McDougal Littell Biology
ATP
H+
2e1
2
O2
2H+
H2O
4
3
Water is formed
when oxygen picks
up electronss and
hydrogen ions.
ADP is changed into ATP
when hydrogen ions flow
through ATP synthase.
At the end of cellular respiration, oxygen picks up electrons that have
gone through the chain, forming water. In summary, the products of the
whole process of cellular respiration—including glycolysis—are:
• carbon dioxide (CO2), as a waste product
• water (H2O), as a waste product
• up to 38 ATP
Comparing Cellular Respiration and Photosynthesis
Again, think about how photosynthesis and cellular respiration are
almost opposites of each other. Photosynthesis stores energy from sunlight as chemical energy. Cellular respiration releases chemical energy to
make ATP, the energy molecule that cells can use. Look at the table below,
and think about other similarities and differences between the processes.
PHOTOSYNTHESIS AND CELLULAR RESPIRATION
photosynthesis
cellular respiration
Organelle for process
chloroplast
mitochondrion
Reactants
CO2 and H2O
sugars (C6H12O6) and O2
Electron transport chain
proteins within thylakoid
membrane
proteins within inner mitochondrial membrane
Cycle of chemical reactions
Calvin cycle in stroma of
chloroplasts builds sugar
molecules
Krebs cycle in matrix of
mitochondria breaks down
carbon-based molecules
Products
sugars (C6H12O6) and O2
CO2 and H2O
In the chart above, circle the organelle in which each process
takes place.
4.5 The Big Picture
1. What products of glycolysis are used in cellular respiration?
2. What products of the Krebs cycle are used in the electron transport
chain?
3. What are the products of the whole process of cellular respiration,
including glycolysis?
4. How does the concentration gradient of H+ ions help to make ATP?
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