Cellular Respiration
AP Biology
ATP—Adenosine triphosphate
• The energy currency
of the cell. ATP
powers almost every
energy requiring
process in cells
http://student.ccbcmd.edu/biotutorials/energy/adpan.html
Cellular respiration relies on electron acceptors & electron
carriers
NAD+ is an electron acceptor
NAD+ + e- NADH
NADH is an electron carrier
FAD+ is an electron acceptor
FAD+ + e-  FADH
FADH is an electron carrier
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Key Questions in Cellular Respiration
•
•
•
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What is the purpose of glucose?
When does oxygen get consumed?
When does CO2 get produced?
What are the most important end products?
Cellular Respiration—Four Stages Master Chart
Stage
Stage Name
1
Glycolysis
2
Pyruvate
Oxidation
3
Krebs Cycle
4
Electron
Transport
Location
Reactants Used
Products
Stage 1—Glycolysis
Glycolysis
Glyco—
Lysis—
Step 1
Step 1.
Two ATP molecules
each provide a
phosphate to form a
new 6-carbon
compound. Two
ATP molecules are
used.
Step 1
Step 2
Step 2. The six carbon
compound is split into
two three carbon
molecules of PGAL.
Step 1
Step 2
Step 3
Step 3. The two PGAL
molecules are oxidized
(lose an electron) and
receive a phosphate
group. The electrons
are added to NAD+ to
form NADH
Step 1
Step 2
Step 4. The
Step 3
phosphate groups
added are removed
and each added to
ADP to form ATP. The
result is the formation
of two, three carbon
molecules called
pyruvic acid.
Step 4
Major Outcomes of Glycolysis
• Splits glucose into two molecules of
pyruvate
• Yields a net of 2 ATP molecules
• Produces 2 NADH molecules
Cellular Respiration—Aerobic Respiration
Stage 2: Oxidation of Pyruvate
Steps of Pyruvate Oxidation
1.Pyruvic acid enters the mitochondrial matrix &
reacts with coenzyme A to form acetyl CoA.
2. CO2 is released
3. NAD+ is reduced to NADH
Stage 3: The Krebs Cycle
Step 1. Acetyl CoA (2 C)
combines with OAA (4 C) to
form citric acid (6 C).
Stage 3: The Krebs Cycle
Step 2. Citric Acid releases a
CO2 molecule to form a
five-carbon molecule. A
hydrogen atom is
transferred to NAD+
forming NADH.
Stage 3: The Krebs Cycle
Step 3. The five carbon
molecule releases a CO2
to form a four carbon
compound. NAD+ is
reduced again to NADH &
ATP is formed.
Stage 3: The Krebs Cycle
Step 4. The four carbon
compound releases
another hydrogen to
reduce FAD to FADH.
Stage 3: The Krebs Cycle
Step 5. The four carbon
compound releases
another hydrogen to
reduce NAD+ to NADH.
This regenerates OAA.
Major Outcomes of the Kreb’s Cycle
• Two pyruvic acid molecules convert to two acetyl
CoA molecules
• The acetyl CoA breaks down
• 6 molecules of CO2 are released (waste)
• 2 ATP molecules are produced (energy)
• 8 NADH are formed (fuels ATP synthesis)
• 2 FADH2 are formed (fuels ATP synthesis)
• Oxaloacetic Acid is reformed, regenerating the
cycle
Electron Transport in the Mitochondria
The electron transport
chain lines the inner
membrane of the
mitochondria
Electron Transport in the Mitochondria
Step 1.
NADH & FADH2 release
hydrogen atoms and
regenerate NAD+ and
FAD.
HH+ + e-
Electron Transport in the Mitochondria
Step 2. High energy
electrons move through
the electron transport
chain.
The energy they lose,
pumps the protons (H+) to
the other side of the
membrane.
Electron Transport in the Mitochondria
Step 3. The high
concentration of protons
move through ATP
synthase & form ATP.
Electron Transport in the Mitochondria
Step 4. The protons and
electrons that reenter the
matrix are accepted by
oxygen to form H2O.
Major Outcomes of Electron
Transport Chain
• From one molecule of glucose, each of the eight
NADH generates 3 ATP molecules—24 ATP
molecules are produced
• Each of the two FADH generates 2 ATP
molecules—4 ATP molecules are produced
• Electrons and hydrogen from the two
cytoplasmic NADH (produced in glycolysis) are
transferred into the mitochondria & yield 6 ATP
• Oxygen accepts electrons and protons to form
water as a byproduct
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