AP Biology: Ch. 9AP Biology: Ch. 9

Cellular RespirationCellular Respiration

Principles of Energy ConservationPrinciples of Energy Conservation

As open systems, As open systems, cells require outside cells require outside energy sources to energy sources to perform cellular work.perform cellular work.

Energy flows into Energy flows into most ecosystems as most ecosystems as sunlight, which is sunlight, which is used by producers to used by producers to make food.make food.

FermentationFermentation

Fermentation is an ATP-producing Fermentation is an ATP-producing catabolic pathway in which both electron catabolic pathway in which both electron donors and acceptors are organic donors and acceptors are organic compounds.compounds.

Anaerobic process (does not require Anaerobic process (does not require oxygen)oxygen)

Results in the partial degradation of Results in the partial degradation of sugarssugars

Large-scale fermentation at a winery

Cellular RespirationCellular Respiration

ATP-producing catabolic process in which ATP-producing catabolic process in which the ultimate electron acceptor is an the ultimate electron acceptor is an inorganic molecule, such as oxygen.inorganic molecule, such as oxygen.

Most prevalent and efficient catabolic Most prevalent and efficient catabolic pathway. Begins with glycolysis, includes pathway. Begins with glycolysis, includes the Kreb cycle and electron transport the Kreb cycle and electron transport chain (ETC).chain (ETC).

Exergonic process (releases energy).Exergonic process (releases energy).

Cellular Respiration: EquationCellular Respiration: Equation

Summarized as:Summarized as:

ReactantsReactants: C: C66HH1212OO66 + 6 O + 6 O22 ProductsProducts: 6 CO: 6 CO22 + H + H22O + energyO + energy

(ATP + heat)(ATP + heat)

ATP: Adenosine

triphosphate

Oxidation/Reduction Reaction Oxidation/Reduction Reaction (Redox)(Redox)

Reactions that involve the partial or Reactions that involve the partial or complete transfer of one or more electrons complete transfer of one or more electrons from one reactant to another.from one reactant to another.

Because an electron transfer requires both Because an electron transfer requires both a donor and an acceptor, oxidation and a donor and an acceptor, oxidation and reduction always go together.reduction always go together.

Oxidation/Reduction, cont.Oxidation/Reduction, cont.

A A reducing agentreducing agent loses electrons loses electrons (becomes more positive) and is (becomes more positive) and is oxidizedoxidized..

In In oxidationoxidation, there is a , there is a lossloss of electrons of electrons from a substance.from a substance.

An An oxidizing agentoxidizing agent gains electrons gains electrons (becomes more negative) and is (becomes more negative) and is reducedreduced..

ReductionReduction is the is the additionaddition of electrons to a of electrons to a substance.substance.

Oxidation/Reduction, cont.Oxidation/Reduction, cont.

Oxygen strongly attracts electrons and is a Oxygen strongly attracts electrons and is a powerful oxidizing agent.powerful oxidizing agent.

Chemical energy is released in a redox Chemical energy is released in a redox reaction that relocates electrons closer to reaction that relocates electrons closer to oxygen.oxygen.

Methane combustion as an energy-yielding redox reaction

GlycolysisGlycolysis

Glycolysis occurs in the cytosol Glycolysis occurs in the cytosol (cytoplasm) of the cell.(cytoplasm) of the cell.Produces 4 ATP, but requires 2 ATP to Produces 4 ATP, but requires 2 ATP to convert glucose to 2 glyceraldehyde convert glucose to 2 glyceraldehyde phosphate molecules, which are then phosphate molecules, which are then converted to pyruvate.converted to pyruvate.For each molecule of glucose, glycolysis For each molecule of glucose, glycolysis results in a results in a net gainnet gain of 2 ATP and 2 of 2 ATP and 2 NADH.NADH.

Kreb CycleKreb CycleOccurs in the mitochondrial matrix.Occurs in the mitochondrial matrix.

For every turn of the Kreb cycle:For every turn of the Kreb cycle:

1)1) 2 C enter in the acetyl fragment of Acetyl CoA2 C enter in the acetyl fragment of Acetyl CoA

2)2) 2 different C are oxidized and leave as CO2 different C are oxidized and leave as CO22

3)3) 3 NADH and 1 FADH3 NADH and 1 FADH22 are produced. are produced.

4)4) 1 ATP is produced by substrate-level 1 ATP is produced by substrate-level phosphorylationphosphorylation

5)5) Oxaloacetate is regenerated.Oxaloacetate is regenerated.

**It takes TWO complete turns of the Kreb cycle to **It takes TWO complete turns of the Kreb cycle to completely oxidize one glucose molecule.completely oxidize one glucose molecule.

Electron Transport ChainElectron Transport Chain

Glycolysis and the Krebs cycle produce Glycolysis and the Krebs cycle produce only 4 molecules of ATP per glucose.only 4 molecules of ATP per glucose.

NADH and FADHNADH and FADH22 produced will provide produced will provide the energy to begin the electron transport the energy to begin the electron transport chain.chain.

Oxidative phosphorylation uses energy Oxidative phosphorylation uses energy released from the electron transport chain released from the electron transport chain to power ATP synthesis.to power ATP synthesis.

Pathway of Electron TransportPathway of Electron Transport

ETC is a series of proteins embedded in ETC is a series of proteins embedded in the inner mitochondrial membrane. the inner mitochondrial membrane. Proteins have groups bound to them.Proteins have groups bound to them.During electron transport, the groups During electron transport, the groups alternate between oxidized and reduced alternate between oxidized and reduced states as they accept and donate states as they accept and donate electrons.electrons.Free energy drops as electrons move Free energy drops as electrons move down the chain.down the chain.

ChemiosmosisChemiosmosis

ETC makes no ATP directly, but releases ETC makes no ATP directly, but releases energy used for ATP synthesis.energy used for ATP synthesis.Chemiosmosis is the energy-coupling Chemiosmosis is the energy-coupling mechanism that uses energy stored in the mechanism that uses energy stored in the form of an H+ gradient (proton-motive form of an H+ gradient (proton-motive force) across the membrane to drive force) across the membrane to drive cellular work.cellular work.ATP synthase uses this energy to make ATP synthase uses this energy to make ATP from ADP + PATP from ADP + Pii

Maintaining the H+ GradientMaintaining the H+ Gradient

The ETC pumps H+ from the mitochondrial The ETC pumps H+ from the mitochondrial matrix, across the inner membrane, to the matrix, across the inner membrane, to the intermembrane space.intermembrane space.

The phospholipid bilayer is impermeable to H+, The phospholipid bilayer is impermeable to H+, so ions are not allowed to diffuse back in.so ions are not allowed to diffuse back in.

ATP synthase uses potential energy stored in ATP synthase uses potential energy stored in the proton gradient to make ATP. H+ is allowed the proton gradient to make ATP. H+ is allowed to diffuse through the ATP synthase complex, to diffuse through the ATP synthase complex, causing the phosphorylation of ADP.causing the phosphorylation of ADP.

Versatility of CatabolismVersatility of Catabolism

Respiration can oxidize organic molecules Respiration can oxidize organic molecules other than glucose to form ATP.other than glucose to form ATP.

Carbohydrates, proteins, and fats in the Carbohydrates, proteins, and fats in the diet are hydrolyzed to form intermediate diet are hydrolyzed to form intermediate compounds that enter glycolysis or the compounds that enter glycolysis or the Kreb cycle.Kreb cycle.

Fats provide twice the energy per gram as Fats provide twice the energy per gram as carbohydrates.carbohydrates.