Cellular Respiration

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Cellular Respiration

• Chapter 9

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Energy Flow and Chemical Recycling
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How Do Cells Harvest Chemical Energy?

• Complex Organic Molecules
• 1 2
  3
• Energy to Energy Simpler waste
• do work lost as heat products
• (ATP) with less
• energy

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How ATP Drives Cellular Work
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Oxidation/Reduction

• OXIDATION
• Removal of electrons
• Addition of oxygen
• Removal of hydrogen
• REDUCTION
• Addition of electrons
• Removal of oxygen
• Addition of hydrogen

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REDOX Reactions

• Oxidation and reduction occur together - one
  substance loses electrons and another gains the
  electrons.

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Red-Ox Reactions
Covalently shared electrons move away from C and
H and closer to O. Electrons loose PE as they
move closer to electronegative atoms.
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Respiration

• During cell respiration
• Glucose is being oxidized, it loses electrons to
  become carbon dioxide.
• Oxygen is being reduced, it gains electrons to
  become water.

C6H12O6 6O2 6CO2 6H2O
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Oxidizing Agent

• The oxidizing agent is the recipient of the
  electrons and therefore is the agent responsible
  for the oxidation

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• Why doesnt the oxidation of glucose occur in
  one single step?
• It would be too explosive and not enough
  energy would be harnessed (enzymes lower EA)

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• There are other oxidizing agents for
  respiration, besides oxygen, which is the
  ultimate electron acceptor.

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Electrons fall from organic molecules to oxygen
during respiration.

• C6H12O6 6O2 6CO2 6H2O
• Hydrogen is transferred from glucose to oxygen
• Change in covalent status of electrons
• Respiration takes ENERGY out of storage
• making it available for ATP synthesis.

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NAD

• Nicotinamide Adenine Dinucleotide
• A coenzyme
• Functions as an oxidizing agent during
  respiration
• NAD traps electrons from glucose
• Dehydrogenase enzymes remove a pair of
• H atoms (2 protons and 2 electrons)
• The enzyme delivers both electrons and one proton
  to NAD to form NADH

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DehydrogenaseNAD p 2e-
NADH
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What is the oxidizing agent here?
NAD
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How is energy transferred?

• Change in the covalent status of electrons as
  they are transferred throughout respiration

The electrons begin the journey in an unstable
configuration and end in a stable molecule
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The Electron Transport Chain
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Electron Transport Chain

• Electron carrier molecules are built into the
  inner mitochondrial membrane.
• Each successive carrier has a higher
  electronegativity than the one before it.
• The ETC accepts energy-rich electrons from
  reduced coenzymes
• Electron transfer from NADH to oxygen is
  exergonic (-222kJ/mole, -53kcal/mole)

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Oxidative Phosphorylation

• High energy electrons transferred from
  substrate to NAD are passed down the electron
  transport chain to oxygen, powering ATP synthesis.

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Substrate Level Phosphorylation
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Three Metabolic Stages of Cellular Respiration

• Glycolysis
• cytosol
• partial oxidation of glucose (6C to 3C)
• pyruvate(3C) molecules
• Krebs Cycle
• mitochondrial matrix
• completes oxidation, pyruvate derivative to CO2
• Electron Transport Chain
• inner membrane of mitochondrion
• accepts energized electrons from reduced
  coenzymes
• ATP produced by oxidative phosphorylation

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Energy Input and Output in Glycolysis-An Overview
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Glycolysis
1.
Hexokinase enzyme transfers a phosphate to
glucose
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2.
Phosphoglucoisomerase enzyme rearranges the G6P
to F6P
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3.
Phosphofructokinase enzyme transfers a phosphate
group to F6P to make F1,6bP
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2 ATPs have been invested so far
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4.
The enzyme aldolase splits the F1,6bP into a
pair of isomers.
5.
Isomerase enzyme converts most of the product to
Glyceraldehyde 3 Phosphate (G3P)
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6.
There are 2 glyceraldehyde phosphate molecules
per initial glucose molecule.
dehydrogenase enzyme provides the H for the
reduction of NAD
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Very exergonic reaction. Energy is used to add P
to ADP
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• Phosphoglycerokinase
• transfers P to ATP

• Phosphoglyceromutase
• rearranges the remaining P

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9. Removal of water rearranges substrate
electrons and makes remaining P bond unstable
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10. Pyruvate kinase transfers P. Substrate level
phosphorylation
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Investment Payoff
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The oxidizing agent of Glycolysis

• The oxidising agent of glycolysis is NAD
• Without NAD glycolysis cannot continue
• Glycolysis is anaerobic, it does not require
  oxygen.

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Animation 9.1 Glycolysis
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Formation of Acetyl CoA
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Total Energy Yield So Far

• From Glycolysis
• 2ATPs and 2 NADHs
• From Pyruvate - Acetyl CoA
• 2 NADHs
• From Krebs Cycle
• 2 ATPs, 6NADHs, and 2 FADH2s
• Where is all of the energy?

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IT IS ALL LOCKED IN THE NADH AND THE FADH2
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• Animation 9.3 Krebs Cycle

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Citric Acid Cycle
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So far the ATPs have been generated via
substrate level phosphorylation, now its time
for chemiosmosis
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Chemiosmosis is an energy-coupling mechanism that
uses energy stored in the form of an H gradient
to drive cellular work.
ATP synthase is the enzyme that is used to carry
out the synthesis of ATP
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The Electron Transport Chain

• What is the ETC? Where is it located?
• It is a series of electron carrier molecules,
  that transfer electrons to each other through a
  connected series of redox reactions.
• It is located within the inner membrane of the
  mitochondrion

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Electron Transport Chain
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What is the role of oxygen?

• The highly electronegative oxygen is the only
  molecule capable of receiving the stable electron
  from cytochrome a3.

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Chemiosmosis

• An E coupling mechanism that uses E stored in the
  form of a proton (H) gradient to drive cellular
  work.

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Electron Transport Chain
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The Final Count

• For every NADH produced in the mitochondrion, how
  many ATPs are created via oxidative
  phosphorylation?
• 3
• For every FADH2 produced, how many ATPs are
  created via oxidative phosphorylation?
• 2
• For the 2 NADHs generated in glycolysis how many
  ATPs are created?
• 4-6 (depending on carrier)

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• 2 NADHs from glycolysis ----gt

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• 2 NADHs from glycolysis ----gt4-6 ATPs
• 8 NADHs from the mitochondrial matrix ----gt

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• 2 NADHs from glycolysis ----gt4-6 ATPs
• 8 NADHs from the mitochondrial matrix ----gt 24
  ATPs
• 2 FADH2s from KC -----gt

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• 2 NADHs from glycolysis ----gt 4-6 ATPs
• 8 NADHs from the mitochondrial matrix ----gt 24
  ATPs
• 2 FADH2s from KC -----gt 4 ATPs
• Total ATPs from oxidative phosphorylation

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• 2 NADHs from glycolysis ----gt 4-6 ATPs
• 8 NADHs from the mitochondrial matrix ----gt 24
  ATPs
• 2 FADH2s from KC -----gt 4 ATPs
• Total ATPs from oxidative phosphorylation 32-
  34 ATPs
• ATPs from substrate level phosphorylation
  (glycolysis and Krebs) 4

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• 2 NADHs from glycolysis ----gt4-6 ATPs
• 8 NADHs from the mitochondrial matrix ----gt 24
  ATPs
• 2 FADH2s from KC -----gt 4 ATPs
• Total ATPs from oxidative phosphorylation 32
  ATPs
• ATPs from substrate level posphorylation 4
• GRAND TOTAL 36- 38 ATPs

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• Animation 9.4 The Electron Transport Chain

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Efficiency of Respiration

• The total ?G for the combustion of glucose -686
  kcal/mol.
• Phosphorylation of ADP to ATP stores
  approximately 7.3 kcal/mole
• Respiration efficiency is 7.3 x 38 277.4
  kcal/mole
• 40 of available energy is used
• A car can use only 25 of energy stored in
  gasoline
• Where does the rest of the energy go?

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Variables in ATP yield

• Some mitochondria differ in permeability to
  protons, which effects the proton motive force.
• Proton motive force may be directed to drive
  other cellular processes such as active
  transport.
• ATP yield is inflated by rounding up
• Prokaryotic cellular respiration is slightly
  higher since no mitochondrial membrane used to
  transport electrons from NADH.

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Poisons

• Rotenone blocks the first electron carrier, used
  to poison fish, and insects.
• Cyanide and carbon monoxide block cyt a3, so what
  will the symptoms be?
• Oligomycin - physically blocks the passage of H
  through ATP synthase. It is used on skin to
  combat fungal infections.
• Uncouplers such as dinitrophenol, makes membrane
  leaky to H

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How does glycolysis proceed in the absence of
oxygen?

• What is the oxidizing agent of glycolysis?
• NAD
• How is NAD regenerated so that glycolysis can
  continue?
• Through the ETC.
• How is NAD regenerated in the absence of ETC (no
  oxygen)?

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Alcohol Fermentation

• Glucose to 2 pyruvate makes 2 ATP and 2 NADH
• Pyruvate looses CO2, converts to ethanol
  (reduction)
• 2 NADH oxidized to 2 NAD (recycled)

Net gain is 2 ATP per glucose molecule
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Lactic Acid Fermentation

• Glucose to pyruvate 2 ATPs and 2 NADH
• Pyruvate reduced to 2 lactate
• 2 NADH oxidized to 2 NAD (recycled)

Net gain is 2 ATP per glucose molecule
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