Transcript CH7Cellular-Respiration

Photosynthesis and Cellular Respiration
CH7: Cellular Respiration
Section 3
Photosynthesis and Cellular Respiration
Key Ideas
• How does glycolysis produce ATP?
• How is ATP produced in aerobic respiration?
• Why is fermentation important?
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Photosynthesis and Cellular Respiration
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Glycolysis
• Before you can use energy from food, it must be
released and transferred to ATP.
• The primary fuel for cellular respiration is glucose.
• Glycolysis occurs in the cytoplasm.
Photosynthesis and Cellular Respiration
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Glycolysis, continued
• In glycolysis, enzymes break down one six-carbon
molecule of glucose into two three-carbon pyruvate
molecules.
• The breaking of a sugar molecule by glycolysis results in
a net gain of two ATP molecules.
• This process of glycolysis is anaerobic, or takes place
without oxygen.
Photosynthesis and Cellular Respiration
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Glycolysis, continued
• Glycolysis is the only source of energy for some
prokaryotes.
• Other organisms use oxygen to release even more
energy from a glucose molecule. Metabolic processes
that require oxygen are aerobic.
• In aerobic respiration, the pyruvate product of glycolysis
undergoes another series of reactions to produce more
ATP molecules.
Photosynthesis and Cellular Respiration
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Glycolysis, continued
• Step 1, Breaking Down Glucose
– Two ATP molecules are used to break glucose into
two smaller units.
– Phosphate is attached to these 2 – three carbon
sugars
Photosynthesis and Cellular Respiration
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Glycolysis, continued
• Step 2, NADH Production
– Each of the three carbon sugars react with another
phosphate (not ATP)
– Hydrogen atoms from these compounds transfer to
two molecules of NAD+ resulting in 2 NADH
molecules
Photosynthesis and Cellular Respiration
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Glycolysis, continued
• Step 3, Pyruvate Production
– In a series of 4 reactions, each of the 3 – carbon
sugars are converted into a 3 – carbon molecule of
pyruvate, resulting in 4 ATP molecules.
– 2 ATP molecules were used in step one, 4 ATP
molecules were created so net total for glycolysis is 2
ATP molecules
Photosynthesis and Cellular Respiration
Glycolysis
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Photosynthesis and Cellular Respiration
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Aerobic Respiration
• The first stage of aerobic respiration is the Krebs cycle,
a series of reactions that produce electron carriers.
• The electron carriers enter an electron transport chain,
which powers ATP synthase.
• Up to 34 ATP molecules can be produced from one
glucose molecule in aerobic respiration.
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Aerobic Respiration, continued
Krebs Cycle
• Pyruvate (from glycolysis) is broken down and combined
with other carbon compounds.
• Each time the carbon-carbon bonds are rearranged
during the Krebs cycle, energy is released.
• The total yield of energy-storing products from one time
through the Krebs cycle is one ATP, three NADH, and
one FADH2.
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Aerobic Respiration, continued
Electron Transport Chain
• The second stage of aerobic respiration takes place in
the inner membranes of mitochondria, where ATP
synthase enzymes are located.
• Electron carriers (NADH and FADH2), produced during
the Krebs cycle, transfer energy through the electron
transport chain.
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Aerobic Respiration, continued
ATP Production
• Hydrogen ions diffuse through ATP synthase, providing
energy to produce several ATP molecules from ADP.
• ATP synthase is present on the inner membrane of the
mitochondria.
• H+ ions diffuse through a channel in this enzyme which
provides energy to produce ATP from ADP.
Photosynthesis and Cellular Respiration
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Aerobic Respiration, continued
The Role of Oxygen
• At the end of the electron transport chain, the electrons
combine with an oxygen atom and two hydrogen ions to
form two water molecules.
• If oxygen is not present, the electron transport chain
stops. The electron carriers are not recycled, so the
Krebs cycle also stops.
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Fermentation
• To make ATP during glycolysis, NAD+ is converted to
NADH. Organisms must recycle NAD+ to continue
making ATP through glycolysis.
• The process in which carbohydrates are broken down in
the absence of oxygen is called fermentation.
• Fermentation enables glycolysis to continue supplying
a cell with ATP in anaerobic conditions.
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Fermentation, continued
• In lactic acid fermentation, pyruvate is converted to lactic
acid.
• During alcoholic fermentation, one enzyme removes
carbon dioxide from pyruvate. A second enzyme
converts the remaining compound to ethanol, recycling
NAD+ in the process.
Photosynthesis and Cellular Respiration
Two Types of Fermentation
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Photosynthesis and Cellular Respiration
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Fermentation, continued
Efficiency of Cellular Respiration
• In the first stage of cellular respiration, glucose is broken
down to pyruvate during glycolysis, an anaerobic
process.
• Glycolysis results in a net gain of two ATP molecules for
each glucose molecule that is broken down.
• In the second stage, pyruvate either passes through the
Krebs cycle or undergoes fermentation. Fermentation
recycles NAD+ but does not produce ATP.
Photosynthesis and Cellular Respiration
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Fermentation, continued
Efficiency of Cellular Respiration
• Cells release energy most efficiently when oxygen is
present because they make most of their ATP during
aerobic respiration.
• For each glucose molecule that is broken down, as many
as two ATP molecules are made during the Krebs cycle.
• The Krebs cycle feeds NADH and FADH2 to the electron
transport chain, which can produce up to 34 ATP
molecules.
Photosynthesis and Cellular Respiration
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Visual Concept: Comparing Aerobic and
Anaerobic Respiration
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Summary
• The breaking of a sugar molecule by glycolysis results in
a net gain of two ATP molecules.
• The total yield of energy-storing products from one time
through the Krebs cycle is one ATP, three NADH, and
one FADH2.
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Summary, continued
• Electron carriers transfer energy through the electron
transport chain, which ultimately powers ATP synthase.
• Fermentation enables glycolysis to continue supplying a
cell with ATP in anaerobic conditions.