How Cells Harvest Energy

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How Cells Harvest Energy

• Chapter 9 Outline
• Cellular Energy Harvest
• Cellular Respiration
• Glycolysis
• Oxidation of Pyruvate
• Krebs Cycle
• Electron Transport Chain
• Catabolism of Protein and Fat
• Fermentation

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Cellular Respiration

• Cells harvest energy by breaking bonds and
  shifting electrons from one molecule to another.
• aerobic respiration - final electron acceptor is
  oxygen
• anaerobic respiration - final electron acceptor
  is inorganic molecule other than oxygen
• fermentation - final electron acceptor is an
  organic molecule

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ATP

• Adenosine Triphosphate (ATP) is the energy
  currency of the cell.
• used to drive movement
• used to drive endergonic reactions

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ATP

• Most of the ATP produced in cells is made by the
  enzyme ATP synthase.
• Enzyme is embedded in the membrane and provides a
  channel through which protons can cross the
  membrane down their concentration gradient.
• ATP synthesis is achieved by a rotary motor
  driven by a gradient of protons.

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NAD NADH

• Nicotinamide adenine dinucleotide, NAD, is a
  coenzyme found in all living cells.
• The compound is a dinucleotide, since it consists
  of two nucleotides joined through their phosphate
  groups with one nucleotide containing an
  adenosine ring, and the other containing
  nicotinamide.
• In metabolism, NAD is involved in redox
  reactions, carrying electrons from one reaction
  to another.
• The coenzyme is therefore found in two forms in
  cells NAD is an oxidizing agent it accepts
  electrons from other molecules and becomes
  reduced,
• this reaction forms NADH, which can then be used
  as a reducing agent to donate electrons. These
  electron transfer reactions are the main function
  of NAD.

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NAD NADH
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The Cellular isms

• Metabolism is the set of chemical reactions
  that occur in living organisms in order to
  maintain life.
• These processes allow organisms to grow and
  reproduce, maintain their structures, and respond
  to their environments.
• Usually divided into two categories.
• Catabolism and Anabolism
• Catabolism breaking down
• Anabolism building up

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The Cellular isms

• Catabolism the set of metabolic pathways which
  break down molecules into smaller units and
  release energy.
• Large molecules such as polysaccharides, lipids,
  nucleic acids and proteins are broken down into
  smaller units such as monosaccharides, fatty
  acids, nucleotides and amino acids, respectively.
  
• These processes produce energy

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The Cellular isms

• Anabolism the set of metabolic pathways that
  construct molecules from smaller units.
• These reactions require energy.
• Anabolism is powered by catabolism. Many anabolic
  processes are powered by adenosine triphosphate
  (ATP).
• Anabolic processes tend toward "building up"
  organs and tissues.
• These processes produce growth and
  differentiation of cells and increase in body
  size, a process that involves synthesis of
  complex molecules.

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Glucose Catabolism

• Cells catabolize organic molecules and produce
  ATP in two ways
• substrate-level phosphorylation
• aerobic respiration
• in most organisms, both are combined
• glycolysis
• pyruvate oxidation
• Krebs cycle
• electron transport chain

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Aerobic Respiration
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Stage One - Glycolysis

• For each molecule of glucose that passes through
  glycolysis, the cell nets two ATP molecules.
• Priming
• glucose priming
• cleavage and rearrangement
• Substrate-level phosphorylation
• oxidation
• ATP generation

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Priming Reactions
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Cleavage Reactions
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Energy-Harvesting Reactions
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Recycling NADH

• As long as food molecules are available to be
  converted into glucose, a cell can produce ATP.
• Continual production creates NADH accumulation
  and NAD depletion.
• NADH must be recycled into NAD.
• aerobic respiration
• fermentation

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Recycling NADH
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Stage Two - Oxidation of Pyruvate

• Within mitochondria, pyruvate is decarboxylated,
  yielding acetyl-CoA, NADH, and CO2.

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Stage Three - Krebs Cycle

• Acetyl-CoA is oxidized in a series of nine
  reactions.
• two steps
• priming
• energy extraction

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Overview of Krebs Cycle

• 1 Condensation
• 2-3 Isomerization
• 4 First oxidation
• 5 Second oxidation
• 6 Substrate-level phosphorylation
• 7 Third oxidation
• 8-9 Regeneration and oxaloacetate

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Krebs Cycle
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Krebs Cycle
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Harvesting Energy by Extracting Electrons

• Glucose catabolism involves a series of
  oxidation-reduction reactions that release energy
  by repositioning electrons closer to oxygen
  atoms.
• Energy is harvested from glucose molecules in
  gradual steps, using NAD as an electron carrier.

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Electron Transport
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Stage Four The Electron Transport Chain

• NADH molecules carry electrons to the inner
  mitochondrial membrane, where they transfer
  electrons to a series of membrane-associated
  proteins.

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Electron Transport Chain
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Chemiosmosis
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ATP Generation

• This process begins with pyruvate, the product of
  glycolysis, and ends with the synthesis of ATP

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Theoretical ATP Yield of Aerobic Respiration
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Regulating Aerobic Respiration

• Control of glucose catabolism occurs at two key
  points in the catabolic pathway.
• glycolysis - phosphofructokinase
• Krebs cycle - citrate synthetase

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Control of Glucose Catabolism
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Catabolism of Proteins and Fats

• Proteins are utilized by deaminating their amino
  acids, and then metabolizing the product.
• Fats are utilized by beta-oxidation.

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Cellular Extraction of Chemical Energy
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Fermentation

• Electrons that result from the glycolytic
  breakdown of glucose are donated to an organic
  molecule.
• regenerates NAD from NADH
• ethanol fermentation
• lactic acid fermentation