Inroduction to Cellular Respiration
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Transcript of Inroduction to Cellular Respiration
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Inroduction to Cellular Respiration
• Open systems need energy from outside sources.
• Living organisms are open systems
• Photoautotrophs(plants) capture the suns energy and convert it to chemical energy in the form of organic molecules through anabolic reactions.
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Organic Molecules• Organic molecules are
burned in the presence of O2.
• Some of the chemical energy is used to make ATP which is utilized for cellular work.
• For example, the oxidation of glucose (a catabolic reaction) provides the energy to produce ATP.
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Cellular Respiration
• The the break down of glucose to CO2 and H2O
• The energy released is trapped in the form of ATP for use in all energy consuming activities of the cell
• This process occurs in two phases
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Glycolysis • The first phase is called
glycolysis• Occurs in the cytoplasm• Is an anaerobic
process• Involves the breakdown
of glucose to pyruvic acid.
• The intermediates are oxidized.
• Two ATPs produced by substrate level phosphorylation
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Krebs Cycle
• Occurs in the mitochondrial matrix• Intermediate step between glycolysis and Krebs
cycle removes a carboxyl group from pyruvic acid to produce aceytl CoA.
• Acetyl CoA then enters the Krebs cycle to be oxidized to CO2 and H2O.
• The electrons transferred from the intermediates in the Krebs cycle go the the ETC to make most of the ATP in cellular rerspiration.
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Fermentation• Pyruvic acid will only be
converted to acetyl CoA if oxygen is present.
• I f there is no oxygen pyruvate does not enter the mitochondria.
• Fermemtation occurs and pyruvate is either reduced to lactic acid or ethanol.
• The function of fermentation is restore the oxidized form of NAD+.
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ATP• Energy yielded from
hydrolysis of ATP is used to transfer phosphates from one molecule to another through enzymes.
• The phosphorylated molecule does work for the cell.
• ATP is replenished through cellular respiration.
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ATP Made in Two Ways• Oxidative
Phosphorylation• Uses electron
transport chain to create a proton gradient across the inner mitochondrial membrane.
• Substrate Level Phosphorylation
• Transfer of a phosphate group from an intermediate to ADP to make ATP
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Complexes function in cellular respiration
• NADH Dehydrogenase pumps protons into the inner membrane space to create a gradient.
• Succinate Dehydrogenase oxidizes succinate.
• Cytochrome c redcutase transfers electrons to cytochrome c oxidase.
• Cytochrome c oxidase transfers electrons to 1/2O2 to form H2O.
• ATP Synthase phosphorylates ADP to ATP as protons diffuse back across the inner mitochondrial membrane
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Chemiosomosis• The coupling of the
exorgonic flow of electrons from the oxidation of food to endergonic ATP production.
• Proton gradient is created across the inner mitochondrial membrane
• As protons diffuse back across the membrane ADP is phosphorylated to ATP
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Oxidative Phosphorylation a Closer Look• Highly
electronegative O2 pulls e- down the ETC towards a lower energy state.
• The e- are harvested from glycolysis and the Krebs cycle.
• This exorgonic slide of e- is coupled to ATP synthesis
• For each molecule of glucose oxidized to CO2 and H2O, 36-38 ATPs are made.
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REDOX REACTIONS• Oxidation-reduction
reactions invovle the partial or complete transfer of e- from one reactant to another.
• Oxidation is the complete or partial loss of e-.
• Reduction is the partial or complete gain of e-
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Redox Reactions
• Electron transfer requires both a donor and and an acceptor.
• Not all redox reactions involve the complete transfer of e-, but instead , may change the degree of sharing.
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Respiration and redox Reactions
• Valence e- of carbon and hydrogen lsoe potential energy as they shift toward electronegative oxygen.
• Released energy is used to make ATP• Organic molecules rich in carbon-
hydrogen bonds are excellent fuels.• A mole of glucose yields 686 Kcal when
burned• In cellular respiration, glucose is
graduallly oxidized in a series of enzyme controlled steps during glycolysis and the Krebs cycle.
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NAD+and FAD• Hydrogens stripped from glucose are not passed directly to
oxygen.• They are first passed to NAD+ or FAD.• NAD+ and FAD act as odidizing agents trapping energy rich e-
from food molecules.• These reactions are catalyzed by dehydrogenases.• XH2 + NAD+ --------------X + NADH + H+ • Dehydrogenases take 2 hydrogen atoms molecule being
oxidized.• Two e- and 1 proton are delivered to NAD+ to produce NADH.
The extra proton is released into the sourounding solution.
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NAD+ and the ETC• NADH then drops off
electrons to the ETC which regenerates NAD+.
• FAD picks up 2 hydrogen atoms to become FADH2.
• For every NADH that makes a trip to the ETC 3 ATP’s are made through chemiosomosis.
• For every FADH2 that makes a trip to the ETC 2 ATP’s are made through chemiosomosis