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.

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.

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

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

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.

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+.

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.

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

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

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

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.

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-

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.

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.

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.

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