Transcript Electron Transport Chain

Cellular Metabolism
Biol 105
Lecture 6
Read Chapter 3 (pages 63 – 69)
Metabolism
 Consists of all of the chemical reactions
that take place in a cell
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Metabolism
Animation—Breaking Down Glucose For Energy
http://wps.aw.com/bc_goodenough_boh_4/177/45509/11650544.cw/index.html
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Cellular Metabolism
 Aerobic cellular respiration – requires
oxygen, produces carbon dioxide
 Anaerobic Fermentation – does not require
oxygen
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Summary of Cellular Respiration
Electrons
transferred
by NADH
Blood
vessel
Glucose
Cytoplasm
Electrons
transferred
by NADH
Electrons
transferred
by NADH
and FADH2
Plasma
membrane
Carrier
protein
Citric
Acid
Cycle
Transition
Reaction
Glycolysis
glucose
pyruvate
Electron
Transport
Chain
Oxygen
Mitochondrion
Extracellular fluid
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+2 ATP
+2 ATP
+32 ATP

36 ATP
Figure 3.27
Aerobic Cellular respiration
 In aerobic cellular respiration cells take in
sugar (glucose) and breaks it down to into
carbon dioxide and water, this requires
oxygen.
 This process produces energy in the form
of ATP
 C6H12O6 + 6O2 → 6CO2 +6H2O + Energy
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Aerobic Cellular respiration

There are four steps of aerobic cellular
respiration:
1.
2.
3.
4.
Glycolysis
Transition Reaction
Citric Acid Cycle (Krebs Cycle)
Electron Transport Chain
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NADH and FADH2 are important carriers of electrons
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Cellular Respiration - Glycolysis
 Phase 1: Glycolysis
 Occurs in the cytoplasm
 Splits one glucose into two pyruvate molecules
 Generates a net gain of 2 ATP and 2 NADH
molecules
 Does not require oxygen
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Cellular Respiration - Glycolysis
 Starts with glucose
 Ends with 2 ATP, 2 NADH, 2 pyruvate
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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
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
In Cytosol
Cellular Respiration – Transition Reaction
 Phase 2: Transition reaction
 Occurs within the mitochondria
 Coenzyme A combines with pyruvate and
CO2 is removed from each pyruvate
 Forms 2 acetyl CoA molecules
 Produces 2 NADH
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Transition Reaction
 Start with:
 2 pyruvate (3 carbon molecules)
 2 Coenzyme A
 End with:
 2 CO2
 2 NADH
 2 Acetyl CoA (2 carbon molecule)
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Transition Reaction
Transition Reaction (in mitochondrion)
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+
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
Cellular Respiration – Citric acid cycle
 Phase 3: Citric acid cycle
 Occurs in the mitochondria
 Acetyl CoA enters the citric acid cycle
 Releases 2 ATP, 2 FADH2 and 6 NADH, 4
CO2 molecules
 Requires oxygen
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Citric Acid Cycle
 Also called the Krebs Cycle
 Start with 2 Acetyl CoA
 End with:
 4 CO2
 2 ATP
 6 NADH and 2 FADH2
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Citric Acid Cycle
Citric Acid Cycle (in mitochondrion)
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
Citrate
NADH
CO2
leaves
cycle
NAD+
Malate
Citric Acid Cycle
NAD+
NADH
FADH2
ATP
FAD
ADP + Pi
-Ketoglutarate
Succinate
CO2 leaves cycle
NAD+
NADH
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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
Cellular Respiration
 Phase 4: Electron transport chain
 Electrons of FADH2 and NADH are
transferred from one protein to another, until
they reach oxygen
 Releases energy that results in 32 ATP
 Requires oxygen
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The Big Pay Off – Electron Transport Chain
 NADH and FADH2 are important carriers of
electrons
 They donate electrons to the electron transport
chain
 At the end of the chain oxygen accepts the
electrons.
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The Big Pay Off – Electron Transport Chain
 Electron Transport Chain produces ATP using the
ATP synthase protein molecule
 The Electron Transport Chain produces 32 ATP
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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.
High
NADH
NAD+
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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H2O
1
2 H+ + 2 O 2
Figure 3.26
How is ATP made using the ETC
1. In the mitochondria, the NADH and FADH
donate electrons to the electron transport chain
(ETC)
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 intermembrane space.
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How is ATP made using the ETC
4. The ATPsynthase transports the H+ back to the
lumen of the mitochondria.
5. The H+ falling through the ATPsynthase
provides the energy for the ATPsynthase to
catalyze the reaction of ADP + P →ATP
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Summary of Cellular Respiration
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Table 3.5
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 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
 The Transition Reaction produces CO2 and
NADH
 The Citric acid cycle: Produces 2 ATP but
also produces lots of NADH and FADH2.
Produces CO2.
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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 molecule.
 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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Complex Carbohydrates
must first be broken
down into glucose before
entering glycolysis
Fats and proteins enter
the process at different
steps
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Oxygen
 Cellular respiration requires oxygen – this 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 only
glycolysis
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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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Anaerobic Fermentation
 Anaerobic Fermentation: Anaerobic pathway
to produce ATP from glycolysis without the
Krebs and ETC
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Fermentation in Animals
 When cells need energy quick they will use this
pathway for a short time
 2 pyruvic acid + 2 NADH → 2 lactate and 2
NAD+
 End result = lactate and 2 ATP produced (from
glycolysis) and NAD+ is regenerated
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What is the starting molecule of glycolysis?
1.
2.
3.
4.
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
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Which stage uses O2
1. Glycolysis
2. Krebs Cycle
3. Electron
Transport Chain
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Which stage produces the most NADHs
1. Glycolysis
2. Krebs Cycle
3. Electron
Transport Chain
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Which stage produces the most ATP
1. Glycolysis
2. Krebs Cycle
3. Electron
Transport Chain
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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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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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