Download Biochem19_Aerobic Respiration

Aerobic Respiration
& Energy
Production
Dr. Michael P. Gillespie11
Mitochondria
• Mitochondria are football-shaped organelles
that are roughly the size of a bacterial cell.
• They are bound by an outer mitochondrial
membrane and an inner mitochondrial
membrane.
• The space between these membranes is the
intermembrane space and the space inside the
inner membrane is the matrix space.
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Mitochondria
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Mitochondria
• The mitochondria has it’s own genetic
information and is able to make some of its
own proteins.
• Mitochondria grow and multiply in a way that
is very similar to simple bacteria.
• Mitochondria are most likely the descendants
of bacteria that were captured by eukaryotic
cells millions of years ago. Approximately 1.5 X
109 years ago.
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Outer Mitochondrial Membrane
• The outer mitochondrial membrane has small
pores through which small molecules can pass.
• The molecules that are oxidized for the
production of ATP are small enough to easily
enter the mitochondrial membrane.
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Inner Mitochondrial
Membrane
• The inner membrane is highly folded to create
a large surface area.
• The folded membranes are known as cristae.
• The inner membrane is almost completely
impermeable.
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Inner Mitochondrial
Membrane
• Transport proteins bring specific food
molecules into the matrix space.
• The protein electron carriers of the electron
transport system are embedded within the
inner membrane.
• ATP synthase is embedded in the membrane.
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Origin Of Mitochondria
• Mitochondria are roughly the size of bacteria.
• Mitochondria have their own genetic information
(DNA).
• They make their own ribosomes that are very
similar to those of bacteria.
• The DNA and ribosomes allow the mitochondria to
synthesize their own proteins.
• Mitochondria are self-replicating. They grow in
size and divide to produce new mitochondria.
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Glucose Utilization
• Under anaerobic conditions, glucose is broken
down into two pyruvate molecules.
• Very little of the stored potential energy in
glucose is released from this limited
degradation of glucose.
• Under aerobic conditions the cells can use
oxygen and completely oxidize glucose to CO2
in a metabolic pathway called the citric acid
cycle.
Dr. Michael P. Gillespie
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Citric Acid Cycle
• Often referred to as the Krebs cycle in honor
of Sir Hans Krebs who elucidated the steps of
this cyclic pathway.
• Also called the tricarboxylic acid (TCA) cycle
because several of the early intermediates in
the pathway have three carboxyl groups.
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Pyruvate Conversion To
Acetyle CoA
• When pyruvate enters the mitochondria, it must
be converted to a two-carbon acetyl group.
• The acetyl group must be activated to enter into
Krebs cycle.
• It is activated when it is bonded to coenzyme A.
• Acetyle CoA is the “activated” form of the acetyl
group.
Dr. Michael P. Gillespie
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Pyruvate Conversion To
Acetyle CoA
• Four coenzymes from four different vitamins
are necessary for this reaction to occur.
• Thiamine pyrophosphate from thiamine
(Vitamin B1)
• FAD derived from riboflavin (Vitamin B2)
• NAD+ derived from niacin
• Coenzyme A derived from pantothenic acid
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Aerobic Respiration
• Aerobic respiration is the oxygen-requiring
breakdown of food molecules and production
of ATP.
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Compartments of
Mitochondria
• Different steps of aerobic respiration occur in
different compartments of the mitochondria.
• The enzymes for the citric acid cycle are found
in the mitochondrial matrix.
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Compartments of
Mitochondria
• Electrons from NADH and FADH2 are passed
through the electron transport system located
in the inner mitochondrial membrane.
• This transfer of electrons causes protons to be
pumped out of the mitochondrial matrix into
the intermembrane compartment (resulting in
a high energy H+ reservoir.
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Compartments of
Mitochondria
• The high energy H+ reservoir is used to make
ATP. The enzyme ATP synthase facilitates this
step.
• The protons flow back into the mitochondrial
matrix through a pore in the ATP synthase
complex and ATP is generated.
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The Citric Acid Cycle
• The citric acid cycle is the final stage of the
breakdown of carbohydrates, fats, and amino
acids.
• The following steps will follow the acetyl
group of an acetyle CoA as it passes through
the citric acid cycle.
• Pyruvate was converted to acetyl CoA when it
entered the mitochodria, thus preparing it for
entry into Krebs cycle.
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Krebs Cycle
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Reaction 1
• 4-Carbon Oxaloacetate combines with Acetyle
CoA to yield 5-carbon Citrate and Coenzyme A.
• Citrate Synthase catalyzes this reaction.
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Reaction 2
• Citrate is isomerized to Isocitrate.
• Aconitase catalyzes this reaction in two steps.
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Reaction 3
• Isocitrate is oxidated to α-ketoglutarate.
• CO2 is released.
• NAD+ is reduced to NADH.
• Isocitrate dehydrogenase catalyzes this
reaction.
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Reaction 4
• 5-carbon α-ketoglutarate is converted to 4carbon Succinyl CoA.
• A carboxylate group is lost in the form of CO2.
• NAD+ is reduced to NADH.
• The enzyme α-ketoglutarate dehydrogenase
catalyzes this reaction.
• Coenzyme A assists.
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Reaction 5
• Succinyl CoA is converted to Succinate.
• An inorganic phosphate is added to GDP to create
GTP.
• The enzyme Succinyl CoA synthase catalyzes this
reaction.
• Coenzyme A is restored.
• Dinucleotide diphosphokinase transfers a
phosphoryl group from GTP to ADP to make ATP.
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Reaction 6
• Succinate is converted into Fumarate.
• FAD is reduced to FADH2.
• Succinate dehydrogenase catalyzes this
reaction.
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Reaction 7
• Fumarate is converted into Malate.
• The enzyme Fumarase catalyzes this reaction.
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Reaction 8
• Malate is converted back into Oxaloacetate.
• The citric acid cycle began with this product so
we have come full circle.
• NAD+ is reduced to NADH.
• Malate dehydrogenase catalyzes this reaction.
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Dr. Michael P. Gillespie
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Point to Remember
• Recall that for every glucose molecule that
was degraded in glycolysis, two molecules of
pyruvate were created.
• Therefore, two turns of the TCA cycle happen
for every molecule of glucose.
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Important Products From The
TCA Cycle
• Per turn of the TCA cycle
• 1 ATP
• 3 NADH
• 1 FADH2
• Per glucose molecule
• 2 ATP
• 6 NADH
• 2 FADH2
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Important Products From
The TCA Cycle
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Krebs Cycle Products
Acetyl CoA
Oxaloacetate
Citrate
Malate
Isocitrate
αKetoglutarate
Fumarate
Succinate
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Succinyl CoA
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Krebs Mnemonic
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Oxidative Phosphorylation
• Electrons carried by NADH can be used to
produce three ATP molecules.
• Electrons carried by FADH2 can be used to
produce two ATP molecules.
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Oxidative Phosphorylation
• Electron transport systems are embedded
within the mitochondrial inner membrane.
• These electron carriers pass electrons from
one carrier in the membrane to the next.
• Protons (H+) can be pumped from the
mitochondrial matrix to the intermembrane
space at three sites in the electron transport
system.
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Oxidative Phosphorylation
• At each site, enough H+ are pumped into the
H+ reservoir to produce one ATP molecule.
• A multiprotein complex called ATP synthase
catalyzes the phosphorylation of ADP to
produce ATP.
• There is a channel in the ATP synthase through
which H+ pass. The energy of the flow of H+ is
harvested to make ATP.
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ATP Yield From Aerobic
Respiration
• 2 ATP / glucose from glycolysis
• 34 ATP / glucose from aerobic respiration
• 26 ATP / glucose
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ATP Yield From Aerobic
Respiration
• Glycolysis
• Substrate level phosphorylation – 2 ATP
• 2 NADH X 2 ATP / cytoplasmic NADH – 4 ATP
• Conversion of 2 pyruvate molecules to 2 acetyl CoA
molecules
• 2 NADH X 3 ATP / NADH – 6 ATP
• Citric Acid Cycle (2 Turns)
• 2 GTP X 1 ATP / GTP – 2 ATP
• 6 NADH X 3 ATP / NADH – 18 ATP
• 2 FADH2 X 2 ATP / FADH2 – 4 ATP
• 36 ATP Total
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