Chapter 9 Cellular Respiration Harvesting Chemical Energy

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Chapter 9Cellular RespirationHarvesting
Chemical Energy
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A. Fermentation

• An ATP producing catabolic pathway in which
  both electron donors and acceptors are organic
  compounds
• Anaerobic Process
• Results in partial degradation of sugars

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B. Cellular respiration

• - An ATP producing catabolic process in which the
  ultimate electron acceptor is oxygen
• Prevalent and efficient
• Carbohydrates, proteins and fats can be
  metabolized, but most often described as
  oxidation of glucose
• C6H12O6 6O2 ? 6CO2 6H2O Energy (ATP heat)

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II. ATP Adenosine Triphosphate

• Nucleotide with unstable phosphate bonds that the
  cell hydrolyzes for energy to drive endergonic
  reactions

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• Phosphorylation ATP transfers terminal
  phosphate to another compound causing it to
  become more reactive
• Phosphorylated compound loses its phosphate group
  as cellular work is performed
• Respiration provides energy to regenerate ATP

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III. Respiration and Redox Reactions
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A. Oxidation-reduction Reactions

• Chemical reactions which involve a partial or
  complete transfer of electrons from 1 reactant to
  another (redox)

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• Oxidation Partial or complete loss of electrons
• Loses energy
• Acts as reducing agent
• Reduction
• Partial or complete gain of electrons
• Acts as an oxidizing agent
• Electrons lose potential energy when they shift
  toward more electronegative atoms

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B. Respiration is a redox process that transfers
hydrogen from sugar to oxygen

• Nicotinamide adenine dinucleotide (NAD) a
  dinucleotide that functions as a coenzyme that
  assists enzymes in electron transfer during redox
  reactions of metabolism
• Coenzyme Small nonprotein organic molecule
  required for certain enzymes to function

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• Dehydrogenases
• Remove a pair of hydrogen atoms (2 electrons and
  2 protons) from the substrate
• Deliver the 2 electrons and one proton to NAD
• Release the remaining proton to the surrounding
  solution

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IV. Cellular Respiration An Overview3 stages
of cellular respiration
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• Glycolysis is a catabolic pathway that
• Occurs in the cytosol
• Partially oxidizes glucose (6C) into 2 pyruvate
  (3C) molecules

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• Krebs Cycle is a catabolic pathway that
• Occurs in the mitochondrial matrix
• Completes glucose oxidation by breaking down a
  pyruvate derivative (acetyl CoA) into carbon
  dioxide

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• Electron Transport Chain
• Located in the inner membrane of the
  mitochondrion
• Accepts energized electrons from NADH and FADH
  (harvested from glycolysis and Krebs) Oxygen
  pulls electrons down ETC to lower energy state
• Couples electron slide with oxidative
  phosphorylation

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• Oxidative Phosphorylation ATP production that
  is coupled to the exergonic transfer of electrons
  from food to oxygen. Occurs in the ETC.

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• Substrate-level phosphorylation ATP production
  by direct enzymatic transfer of phosphate from an
  intermediate substance in catabolism to ADP.
  Occurs during glycolysis and Krebs.

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V. Glycolysis Splitting of the glucose molecule

• Occurs in 2 phases
• Energy-investment phase The cell uses ATP to
  phosphorylate the intermediates of glycolysis
• Energy-yielding phase Two 3-carbon
  intermediates are oxidized. For each glucose
  molecule entering glycolysis
• A net gain of two ATPs is produced by substrate
  level phosphorylation
• 2 molecules of NAD are reduced to NADH. Energy
  conserved in the high-energy electrons of NADH
  can be used to make ATP by oxidative
  phosphorylation
• Steps (see book)

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VI. Krebs Cycle

• Fate of pyruvate
• Depends upon the presence or absence of oxygen
• If oxygen is present, pyruvate enters the
  mitochondrion where it is completely oxidized by
  a series of enzyme-controlled reactions

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• Formation of Acetyl CoA Junction between
  glycolysis and Krebs
• Pyruvate molecules translocated from cytosol into
  mitochondrion by carrier protein. Catalyzed by
  multienzyme complex which
• Removes CO2 from carboxyl
• Oxidizes two-carbon fragment to acetate while
  reducing NAD to NADH
• Attaches coenzyme A to acetyl group. Bond is
  unstable acetyl group reactive
• Steps of the cycle (see handout and overhead)

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VII. Electron Transport and Oxidative
Phosphorylation

• Electron transport
• At the end of the Krebs Cycle, most of the energy
  extracted from glucose is in molecules of NADH
  and FADH2
• These reduced coenzymes pass their electrons down
  the ETC to oxygen.
• Exergonic transfer of electrons down the ETC to
  oxygen is coupled to ATP synthesis
• Each successive carrier in the chain had a higher
  electronegativity than the carrier before it
  oxygen most electronegative
• STEPS See overhead

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• Chemiosmosis Coupling The coupling of exergonic
  electron flow down an electron transport chain to
  endergonic ATP production by creation of a
  protein gradient across a membrane. The protein
  gradient drives ATP synthesis as protons diffuse
  back across the membrane
• Coupling between chemical reactions
  (phosphorylation) and transport process (proton
  transport)
• ATP synthase, an enzyme found in the inner
  mitochondrial membrane, makes ATP

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VIII. Cell Respiration Summary
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For every NADH entering the ETC, 3 ATP is
produced For every FADH2 entering the ETC, 2 ATP
is produced
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IX. Fermentation

• Aerobic Existing in the presence of oxygen
• Anaerobic Existing in the absence of free oxygen

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• Fermentation Anabolic catabolism of organic
  nutrients
• Glycolysis oxidizes glucose to 2 pyruvate
  molecules oxidizing agent NAD, not oxygen
• Fermentation recycles NAD from NADH
• Steps Glycolysis followed by alcohol
  fermentation or lactic acid fermentation

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a. Alcohol fermentation

• Pyruvate loses carbon dioxide converted to
  2-carbon compound acetaldehyde
• NADH is oxidized to NAD and acetaldehyde is
  reduced to ethanol
• Many bacteria and yeast carry out alcohol
  fermentation under anaerobic conditions

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b. Lactic Acid Fermentation

• NADH is oxidized to NAD and pyruvate is reduced
  to lactate
• Fungi and bacteria
• Products include cheese and yogurt
• Human muscle cells during strenuous exercise