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2/4/17
Metabolism
§  Consists of all of the chemical reactions
that take place in a cell.
Cellular Metabolism
§  Can be reactions that break things down.
(Catabolism)
§  Or reactions that build things up.
(Anabolism)
Biol 105
Read Chapter 3 (pages 63 – 69)
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Cellular Metabolism
§  Some of the reactions provide energy for
the cell in the form of ATP.
§  Aerobic Cellular Respiration – requires
oxygen, produces carbon dioxide.
§  Anaerobic Fermentation – does not require
oxygen, does not produce carbon dioxide.
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Summary of Cellular Respiration
Electrons
transferred
by NADH
Blood
vessel
Glucose
Aerobic Cellular respiration
Cytoplasm
Electrons
transferred
by NADH
Electrons
transferred
by NADH
and FADH2
Plasma
membrane
Carrier
protein
Citric
Acid
Cycle
Transition
Reaction
Glycolysis
glucose
pyruvate
§  This process produces energy in the form of
ATP
Electron
Transport
Chain
§  C6H12O6 + 6O2 → 6CO2 +6H2O + Energy (ATP)
Oxygen
Mitochondrion
Extracellular fluid
+2 ATP
§  In aerobic cellular respiration cells take in sugar
(glucose) and break it down to into carbon
dioxide and water, this requires oxygen and
produces CO2.
+2 ATP
+32 ATP
=
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36 ATP
Figure 3.27
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Aerobic Cellular respiration
§  There are four steps in aerobic cellular
respiration:
1.  Glycolysis
2.  Transition Reaction
3.  Citric Acid Cycle (Krebs Cycle)
4.  Electron Transport Chain
Name, Location, Require O2?, Starting Molecule(s),
Ending Molecule, #ATP, #NADH, #FADH2, #CO2
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Cellular Respiration - Glycolysis
Cellular Respiration - Glycolysis
§  Phase 1: Glycolysis
§  Starts with:
§  1 glucose (6 carbon molecule)
§  (2 ATP)
§  Occurs in the cytoplasm.
§  Does not require Oxygen
§  Splits one glucose into two pyruvate
molecules.
§  Ends with:
§  2 ATP
§  2 NADH
§  2 pyruvate (3 carbon molecule)
§  Forms 2 Pyruvate Molecules
§  Produces 2 ATP + 2 NADH
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Glycolysis
Glycolysis (in cytoplasm)
Cytoplasm
During the first steps,
two molecules of ATP are
consumed in preparing
glucose for splitting.
Glucose
During the remaining
steps, four molecules
of ATP are produced.
2 ATP
Energyinvestment
phase
2 ADP
In Cytosol
4 ADP
4 ATP
The two molecules of
pyruvate then diffuse
from the cytoplasm into
the inner compartment
of the mitochondrion,
where they pass through
a few preparatory steps
(the transition reaction)
before entering the citric
acid cycle.
2 NAD+
2 NADH
2 Pyruvate
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Energyyielding
phase
Two molecules of nicotine
adenine dinucleotide
(NADH), a carrier of
high-energy electrons,
also are produced.
Figure 3.23
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Cellular Respiration – Transition Reaction
§  Phase 2: Transition Reaction (Intermediate Phase)
§  Starts with:
§  2 pyruvate (3 carbon molecule)
§  2 Coenzyme A
§  Occurs within the mitochondria.
§  Requires Oxygen.
§  Coenzyme-A combines with pyruvate and a
CO2 is removed from each pyruvate.
§  Ends with:
§  2 CO2
§  2 NADH
§  2 Acetyl CoA (2 carbon molecule)
§  Forms 2 acetyl CoA molecules.
§  Produces 2 NADH.
§  Produces 2 CO2.
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Transition Reaction
Cellular Respiration – Citric acid cycle
Transition Reaction (in mitochondrion)
§  Phase 3: Citric Acid Cycle (Krebs Cycle)
§  Occurs in the mitochondria.
§  Requires Oxygen.
§  2 Acetyl CoA enter the citric acid cycle and
combine with oxaloacetate.
§  Oxaloacetate re-forms.
§  Produces:
§ 2 ATP
§ 2 FADH2
§ 6 NADH
§ 4 CO2
Pyruvate (from glycolysis)
One carbon (in the form
of CO2) is removed
from pyruvate.
A molecule of NADH is
formed when NAD+
gains two electrons
and one proton.
CO2
NAD+
In
Mitochondria
Transition Reaction
Coenzyme A
NADH
(electron passes
to electron
transport chain)
CoA
Acetyl CoA
The two-carbon
molecule, called
an acetyl group,
binds to
coenzyme A
(CoA), forming
acetyl CoA,
which enters the
citric acid cycle.
Citric Acid Cycle
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Figure 3.24
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Citric Acid Cycle
Citric Acid Cycle
§  Also called the Krebs Cycle
Citric Acid Cycle (in mitochondrion)
§  Starts with:
§  2 Acetyl CoA (2 carbon molecule)
§  Oxaloacetate
Acetyl CoA, the
two-carbon compound
formed during the
transition reaction,
enters the citric acid
cycle.
The citric acid cycle also
yields several molecules of
FADH2 and NADH, carriers of
high-energy electrons that
enter the electron transport
chain.
Acetyl CoA
CoA
CoA
Oxaloacetate
§  Ends with:
§  4 CO2
§  2 ATP
§  6 NADH
§  2 FADH2
§  Oxaloacetate
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Citrate
NADH
CO2
leaves
cycle
NAD+
Malate
Citric Acid Cycle
NADH
FADH2
ATP
FAD
In
Mitochondria
NAD+
ADP + Pi
α-Ketoglutarate
Succinate
NAD+
NADH
CO2 leaves cycle
The citric acid cycle yields
One ATP from each acetyl
CoA that enters the cycle,
for a net gain of two ATP.
Figure 3.25
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NADH and FADH
§  NADH and FADH2 are important carriers of electrons
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The Big Pay Off – Electron Transport Chain
Cellular Respiration
§  NADH and FADH2 are important carriers of
electrons.
§  Phase 4: Electron Transport Chain
§  Electrons of FADH2 and NADH are
transferred from one protein to another, until
they reach oxygen.
§  Requires oxygen.
§  Releases energy that results in 32 ATP.
§  They donate electrons to the electron transport
chain.
§  At the end of the chain oxygen accepts the
electrons.
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Copyright © 2009 Pearson Education, Inc.
Electron Transport Chain
Electron Transport Chain (inner membrane of mitochondrion)
The molecules of NADH and
FADH2 produced by earlier phases
of cellular respiration pass their
electrons to a series of protein
molecules embedded in the inner
membrane of the mitochondrion.
Inner
Membrane of
Mitochondria
High
NAD+
NADH
As the electrons are transferred
from one protein to the next,
energy is released and used to
make ATP.
Potential energy
2e–
FADH2
Membrane
proteins
2e–
FAD
2e–
2e–
Eventually, the
electrons are
passed to oxygen,
which combines
with two hydrogens
to form water.
2e–
Low
Energy released is used
for synthesis of ATP
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2 H+ +
H 2O
1
2
O2
Figure 3.26
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The Big Pay Off – Electron Transport Chain
§  Electron Transport Chain produces ATP
using the ATP Synthase protein.
§  The Electron Transport Chain produces 32
molecules of ATP.
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How is ATP made using the ETC
How is ATP made using the ETC
1.  In the mitochondria NADH and FADH2 donate
electrons to the electron transport chain (ETC).
4.  ATP Synthase allows the H+ to flow down
it’s concentration gradient back to the lumen
of the mitochondria.
2.  Oxygen is the final electron acceptor from the
ETC.
3.  The ETC uses the energy from the electrons to
transport H+ against the concentration
gradient, transporting them from the lumen of
the mitochondria to the inter-membrane space.
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5.  The H+ flowing through the ATP Synthase
provides the energy for the ATP Synthase
to catalyze the reaction of ADP + P → ATP.
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Summary of Cellular Respiration
Summary of Cellular Respiration
§  One molecule of glucose is broken down
and 36 ATP are generated.
§  Oxygen is used by the electron transport
chain – it accepts electrons from the end
of the ETC.
§  Carbon dioxide is produced by the
Transition Reaction and the Citric Acid
Cycle.
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Summary of Cellular Respiration
§  Glycolysis: Starts the process by taking in
glucose.
§  Produces 2 ATP & 2 NADH.
§  The Transition Reaction:
§  Produces 2 CO2 and 2 NADH.
§  The Citric Acid Cycle:
§  Produces 2 ATP but also produces 6 NADH
and 2 FADH2.
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Table 3.5
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Summary of Cellular Respiration
§  Electron transport chain
§  Takes electrons from NADH and FADH2
and uses them to produce ATP using the
ATP Synthase protein.
§  Requires oxygen: Oxygen is the final
electron acceptor on the electron
transport chain.
§  One glucose can produce a total of 36 ATP
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Sources of Energy
Complex Carbohydrates
must first be broken
down into glucose before
entering glycolysis
O
H2N
CH
C
Fats and proteins enter
the process at different
steps
OH
R
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Copyright © 2009 Pearson Education, Inc.
Animation
§  Respiration Movie
Oxygen
§  Cellular respiration that requires oxygen is
Aerobic Cellular Respiration.
§  Sometimes organisms, including humans,
need to produce energy without using
oxygen.
§  When you need energy quick, or if there is
not enough O2 then the cell will use
Anaerobic Fermentation.
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Anaerobic Fermentation
§  Anaerobic Fermentation:
§  Use the anaerobic pathway to produce
ATP from glycolysis without the
Transition Reaction, Citric Acid Cycle or
the ETC
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Anaerobic Fermentation
§  Breakdown of glucose without oxygen.
§  Takes place entirely in the cytoplasm.
§  It is very inefficient - results in only two ATP.
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Fermentation in Animals
§  When cells need energy quick they will use
this pathway for a short time.
§  Glycolysis → 2 pyruvic acid + 2 NADH→
→ 2 lactate (lactic acid) and 2 NAD+.
§  End result = lactate and 2 ATP produced
(from glycolysis) and NAD+ is regenerated
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Acetyl CoA
Protein
Glucose
Pyruvate (pyruvic
acid)
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Which stage produces CO2
1.  Glycolysis
2.  Electron
Transport Chain
3.  Transition
4.  Citric acid Cycle
5.  Both 3 and 4
1.  Glycolysis
2.  Electron
Transport Chain
3.  Transition
4.  Citric acid Cycle
5.  Both 3 and 4
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4. 
What is the starting molecule of glycolysis?
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What is the starting molecule of glycolysis?
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Which stage uses O2
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2.  Citric Acid (Krebs)
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3.  Electron
Transport Chain
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2.  Citric Acid (Krebs)
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3.  Electron
Transport Chain
Which stage produces the most NADHs
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Which stage produces the most NADHs
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2.  Citric Acid (Krebs)
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Which stage uses O2
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Important Concepts
§  Read Ch 4
§  What is Cellular respiration and Anaerobic
Fermentation and what are the differences
between them.
§  What are the four steps of aerobic cellular
respiration, what happens in each step, what
are the starting molecules, what comes out of
each step, where in the cell does each step
occur, how many ATP and NADH/FADH2 are
produced in each step.
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1.  Glycolysis
2.  Krebs Cycle
3.  Electron
Transport Chain
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1.  Glycolysis
2.  Krebs Cycle
3.  Electron
Transport Chain
Which stage produces the most ATP
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Which stage produces the most ATP
Important Concepts
§  Describe in detail how is ATP made using the
electron transport chain
§  What is the role of ATPsynthase, H+, O2, NADH
and FADH2 and the electron transport chain in
ATP production?
§  Know the overall picture of cellular respiration
(summary slides)
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Important Concepts
§  What is the role of oxygen in cellular respiration,
what steps produce carbon dioxide
§  What is anaerobic fermentation, what steps are
involved in fermentation, what end products are
produced in humans, is oxygen required? when is
it used.
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Definitions
§  Aerobic cellular respiration, anaerobic
fermentation , ATP synthase, metabolism
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