Cellular Respiration and Fermentation

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Cellular Respiration and Fermentation

• Chapter 9

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Objectives

• Understand that cellular respiration is a series
  of coupled metabolic processes
• Describe the role of ATP, NAD and FAD in coupled
  reactions
• Know the start and end products of each reaction
• Know the kind and quantity of energy produced by
  each reaction
• Explain how ATP production is controlled

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Objectives continued

• Understand the process of chemiosmosis
• Explain how the slide of electrons down the
  electron transport chain is coupled to the
  production of ATP by chemiosmosis
• Understand the difference between substrate-level
  phosphorylation and oxidative phosphorylation
• Describe the fate of pyruvate during fermentation
• Understand how food molecules other than glucose
  can be oxidized to make ATP
• Understand how anabolic synthesis of carbohydrate
  metabolism can generate the building blocks of
  other macromolecules

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ATP

• Energy molecule used to couple exergonic
  reactions to endergonic
• Nucleotide with three phosphate groups attached
  to the ribose sugar
• ATP has a high ?G

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ATP

• Energy is released from ATP through the loss of
  phosphate groups
• Catabolic reaction resulting from hydrolysis
  producing ADP Pi (inorganic Phosphate) energy
  (?G -7.3Kcal/mol in the lab, -13Kcal/mol in
  the cell)

ATP is synthesized through aerobic and
anaerobic pathways
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Cellular Respiration is a Redox Reaction

• Method of energy release is gradual and methodic
• increases efficiency
• enzyme catalyzed
• Hydrogen atoms removed from foods as they are
  oxidized are added to NAD resulting in reduction
  to NADH H

This process is assisted by enzymes generically
referred to as Dehydrogenases
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Overview

• Aerobic cellular respiration has 4 steps
• Glycolysis
• in cytosol
• Transition reaction
• at mitochondrial membrane
• Krebs cycle
• in mitochondrial matrix
• Electron Transport Chain
• at inner membrane of mitochondria

C6H1206 6O2?6CO2 6H20 ENERGY
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Glycolysis

• Start with glucose (C6H1206)
• End product is 2x Pyruvate 2(C3H4O3)
• Some steps are endergonic while others are
  exergonic

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• First obstacle
• make glucose reactive
• Increase free energy of glucose by
  phosphorylation by ATP
• Rearrange molecule
• Increase free energy of glucose by
  phosphorylation with ATP
• phosphofructokinase is an allosteric enzyme that
  controls the rate of glycolysis
• Result in reactive molecule

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• Now that our 6C sugar (fructose 1,6-biphosphate)
  is ready to react, aldolase cleaves it into 2(3C)
  molecules that are isomers (what kind) of each
  other.
• 5 Isomerase converts the unusable
  Dihydroxyacetone phosphate into Glyceraldehyde
  phosphate

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• Each glyceraldehyde phosphate is acted on by the
  enzyme Triose phosphate dehydrogenase that
  oxidized the sugar by reducing NAD and
  sequentially adding inorganic phosphate to the
  sugar
• A molecule of ATP is made from each
  1,3-biphosphoglycerate as the phosphate added in
  step 6 is transferred to ADP
• The molecule is reorganized through the
  relocation of the phosphate group

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• Enolase makes an enol (CC-O) through the removal
  of water resulting in an unstable molecule (prone
  to change)
• 10 Terminal step in glycolysis results in the
  formation of Pyruvate as the enzyme Pyruvate
  kinase transfers the phosphate group of
  phosphoenolpyruvate to ADP forming ATP

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Glycolysis summarized

• Glucose converted into 2 pyruvate
• Energy requiring and energy releasing steps
• Energy net yield is 2ATP and 2NADH
• Enzymes involved at each step
• Kinase conversion of ATP to ADP or ADP to ATP
• Dehydrogenase reduces NAD to NADH while
  oxidizing sugar
• Isomerase/mutase keep reactions moving forward
  through isomer formation
• Regulated by phosphofructokinase activity (step
  3) and the rate of isomer formation of
  glyceraldehyde phosphate (step 5)

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Regulation of Glycolysis

• Phosphofructokinase is regulated by allosteric
  means where
• ADP and AMP activate enzyme
• Citrate (high energy molecule of the Krebs
  cycle) inhibits enzyme
• Also regulated by feedback inhibition

• Isomerase is regulated by enzyme concentration
  and substrate availability

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Mitochondria

• Pyruvate Processing
• at mitochondrial membrane
• Krebs cycle
• in mitochondrial matrix
• Electron Transport Chain
• Across the inner membrane of the mitochondria

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Pyruvate Processing

• Pyruvate is converted into Acetyl-CoA as it is
  transported into the mitochondrion from the
  cytosol
• NAD converted into NADH
• CO2 produced during reaction

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Krebs Cycle

• Each molecule of Acetyl- CoA enters the Krebs
  cycle
• the 2C of acetyl CoA are exchanged for 2 C in
  oxaloacetate
• Each turn of the cycle produces
• 3 NADH
• 1FADH2
• 1ATP
• 2CO2

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• Acetyl CoA enters the krebs cycle by attaching
  to a 4 carbon sugar (Oxaloacetate) forming a six
  carbon sugar (Citrate)
• An isomer of citrate is created through
  condensation/hydrolysis reactions resulting in
  isocitrate
• Isocitrate loses CO2 forming ?-ketoglutarate as
  oxidation of the compound occurs NADH is formed
• ?-ketoglutarate (C5) is converted to Succinyl CoA
  (C4). Along the way, CO2 is released, and NAD
  is reduced

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• Succinyl CoA is converted into Succinate.
  Reaction starts as inorganic phosphate attaches
  to Succinyl CoA displacing CoA. The phosphate is
  picked up by GDP forming GTP. The terminal
  phosphate of GTP is transferred to ADP forming
  ATP
• Succinate is oxidized to Fumarate Reducing FAD to
  FADH2
• The addition of H20 to Fumarate produces Malate
• Oxaloacetate is reformed through the oxidation of
  Malate. NADH is formed during the process

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Regulation of Pyruvate Processing and Krebs
cycle

• The enzyme pyruvate dehydrogenase is regulated by
  several molecules which either inhibit or
  activate its activity.
• Ultimately, pyruvate dehydrogenase activity
  influences the activity of the Krebs cycle
• Feedback inhibition also is used to regulate the
  Krebs cycle

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Electron Transport Chain
Electron shuttling proteins are called
flavoproteins, iron-sulphur proteins, and
cytochromes?
Each protein in the series is more
electronegative than its predecessor

• Each NADH enters the electron transport chain
  with enough free energy to fuel formation of 3
  ATP
• Each FADH2 will yield 2 ATP

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ETC

• Some electron carriers of the transport chain
  carry only electrons
• Ubiquinone
• Cytochrome c
• Some electron carriers accept and release protons
  along with electrons

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Chemiosmosis

• Chemiosmosis coupling of exergonic electron flow
  down an ETC to endergonic ATP production by the
  creation of a proton gradient across a membrane
  (proton-motive force)

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ATP Formation

• ATP synthase couples inorganic phosphate to ADP
  as H return to the matrix (utilizes potential
  energy of proton gradient)
• 1ATP is formed for each H diffusing across the
  membrane

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Substrate-level Phosphorylation ATP production
coupled by direct enzymatic transfer of phosphate
from an intermediate in catabolism to
ADP Oxidative Phosphorylation ATP production
that is coupled to the exergonic transfer of
electrons from food to oxygen
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Variations of Glycolysis Fermentation

• In the absence of oxygen, liberation of energy
  can occur through fermentation pathways yielding
  a max of 2 ATP/glucose
• Fermentation is similar to glycolysis except that
  the end product is not pyruvate because of the
  addition of a few steps necessary to regenerate
  NAD

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What about the other foods?

• Proteins, Carbos and Fats can all be utilized
  for energy following hydrolysis
• Amino Acids are converted to intermediates
  including pyruvate, acetyl CoA, and
  ?-ketoglutarate
• Carbos enter glycolysis at the beginning or as
  Fructose 6 phosphate
• Fats components
• glycerol enters as glyceraldehyde phosphate
• Fatty acids enter as Acetyl CoA

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Anabolic Synthesis of Key Molecules

• Intermediates of Carbohydrate metabolism generate
  the building blocks to manufacture
• Amino acids
• RNA
• DNA
• Phospholipids
• Carbohydrate storage products