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CELLULAR RESPIRATION: CELLULAR RESPIRATION: HARVESTING CHEMICAL HARVESTING CHEMICAL

ENERGYENERGY

Oxidative Phosphorylation and the Oxidative Phosphorylation and the Electron Transport ChainElectron Transport Chain

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ObjectivesObjectives

• The events of the electron transport chain The events of the electron transport chain and chemiosmosis.and chemiosmosis.

• Fermentation (Anaerobic respiration) Fermentation (Anaerobic respiration) enables some cells to produce ATP without enables some cells to produce ATP without the help of oxygen the help of oxygen

3- Electron transport chain:3- Electron transport chain: oxidative phosphorelationoxidative phosphorelation

• Thousands of copies of the electron Thousands of copies of the electron

transport chain are found in the extensive transport chain are found in the extensive

surface of the surface of the cristaecristae ( (the inner membrane of the

mitochondrion).).

• Electrons drop in free energy as they pass Electrons drop in free energy as they pass

down the electron transport chain.down the electron transport chain.

• Only 4 of 38 ATP ultimately produced by respiration of glucose are Only 4 of 38 ATP ultimately produced by respiration of glucose are

derived from substrate-level phosphorylation (derived from substrate-level phosphorylation (2 from glycolysis and 2 2 from glycolysis and 2

from Krebs Cyclefrom Krebs Cycle).).

• The vast majority of the ATP (The vast majority of the ATP (90%90%) comes from the energy in the ) comes from the energy in the

electrons carried by NADH and FADHelectrons carried by NADH and FADH22..

• The energy in these electrons is used in the electron transport The energy in these electrons is used in the electron transport

chain to power chain to power لتدعملتدعم ATP synthesis.ATP synthesis.

The inner mitochondrial membrane couples electron transport to ATP synthesis (90% of The inner mitochondrial membrane couples electron transport to ATP synthesis (90% of ATP)ATP)

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Fig. 9.13

• Electrons from NADNADHH or FADFADHH22 ultimately pass to oxygen.

• The electron transport chain generates no ATP directly. Rather, its function is to breakbreak the largelarge free energy drop from food to oxygen into a seriesa series of smallersmaller steps that release energy in manageable amounts مناسبة .كميات

• Electrons carried by Electrons carried by NADNADHH are transferred to the first molecule in are transferred to the first molecule in the electron transport chain (the electron transport chain (the flavoprotein; FMN).).

• The electrons continue along the chain which includes several The electrons continue along the chain which includes several CytochromeCytochrome proteins and one lipid carrier. proteins and one lipid carrier.

• The electrons carried by The electrons carried by FADFADHH22 have have

lower free energy and are added to lower free energy and are added to a later point in the chain.a later point in the chain.

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• Chemiosmosis:Chemiosmosis: ((osmos = puchosmos = puch)) It is the It is the oxidative phosphorelationoxidative phosphorelation that that

results in ATP production in the inner results in ATP production in the inner membrane of mitochondria.membrane of mitochondria.

• The ATP synthase molecules are the only The ATP synthase molecules are the only place that will allow place that will allow HH++ to diffuse back to to diffuse back to

the matrix the matrix (exergonic flow of H+).• This flow of This flow of HH++ is used by the enzyme to is used by the enzyme to

generate ATP a process called generate ATP a process called chemiosmosis.chemiosmosis.

• ATP-synthaseATP-synthase,, in the cristae actually makes in the cristae actually makes ATPATP from from ADPADP and and PPii..

• ATP used the energy of an existing proton gradient to power ATP ATP used the energy of an existing proton gradient to power ATP synthesis.synthesis.– This This proton gradientproton gradient develops between develops between

the intermembrane space and the matrix. the intermembrane space and the matrix.

– This concentration of This concentration of HH++ is the is the proton-motive forceproton-motive force..

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Fig. 9.15, Page 168

Energy of NADH and FADHEnergy of NADH and FADH22 give a maximum yield give a maximum yield

of of 34 ATP34 ATP is produced by is produced by oxidative phosphorylationoxidative phosphorylation..

• During respiration, most energy flows from During respiration, most energy flows from glucose NADHglucose NADH electron transport chain electron transport chain proton-motive force ATP. proton-motive force ATP.

• Some ATPSome ATP is produced by is produced by substrate-level phosphorylationsubstrate-level phosphorylation during glycolysis and the Krebs cycle, but during glycolysis and the Krebs cycle, but most ATPmost ATP comes comes from from oxidative phosphorylation oxidative phosphorylation (through electron transport chain)(through electron transport chain)..

• Energy produced in Glycolysis and Krebs cycle gives a Energy produced in Glycolysis and Krebs cycle gives a maximum yield of maximum yield of 4 ATP4 ATP by substrate-level phosphorylation. by substrate-level phosphorylation.

• Energy produced in electron transport chain gives a maximum Energy produced in electron transport chain gives a maximum yield of yield of 34 ATP34 ATP by oxidative phosphorylation via ATP-synthase. by oxidative phosphorylation via ATP-synthase.

• Substrate-level phosphorylation and Substrate-level phosphorylation and oxidative phosphorylationoxidative phosphorylation give a bottom line of give a bottom line of 38 ATP.38 ATP.

Cellular respiration generates many ATP molecules for Cellular respiration generates many ATP molecules for each sugar molecule it oxidizeseach sugar molecule it oxidizes

1.1. General electron pathway food→NADH→ETC→oxygen.General electron pathway food→NADH→ETC→oxygen.2.2. ETC is a series of electron carriers located in the inner membrane of the ETC is a series of electron carriers located in the inner membrane of the

mitochondriamitochondria3.3. NADH supplies two electrons to the ETC NADH supplies two electrons to the ETC NADNAD++ + 2H→ NADH + H + 2H→ NADH + H+.+.

4.4. In the ETC electrons move through the chain reducing and oxidizing the In the ETC electrons move through the chain reducing and oxidizing the molecules as they pass.molecules as they pass.

5.5. The ETC is made mostly of proteins.The ETC is made mostly of proteins.6.6. The NADH molecules transport the electrons to the ETC -FADHThe NADH molecules transport the electrons to the ETC -FADH22 is added is added

at a lower energy level.at a lower energy level.7.7. The electrons move down the mitochondrial membrane through the The electrons move down the mitochondrial membrane through the

electron carrierselectron carriers8.8. A concentration gradient is generated -positive in the intermembrane A concentration gradient is generated -positive in the intermembrane

space.space.9.9. At the end of the ETC oxygen accepts hydrogen and one electron to At the end of the ETC oxygen accepts hydrogen and one electron to

form water.form water.10.10. The HThe H++ ions that passed through the proteins into the cytoplasm flow ions that passed through the proteins into the cytoplasm flow

through ATP synthase into the mitochondrial matrix.through ATP synthase into the mitochondrial matrix.11.11. The energy generated by the proton movement creates ATP by joining The energy generated by the proton movement creates ATP by joining

ADP and PADP and Pi.i.

12.12. NADH produces 3 ATP per molecule.NADH produces 3 ATP per molecule.13.13. FADHFADH22 produces 2 ATP per molecule produces 2 ATP per molecule

Summary of Electron Transport Chain (ETC)Summary of Electron Transport Chain (ETC)

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Summary ofSummary of Cellular Cellular Respiration Respiration

- Glycolysis- Glycolysis occurs in the cytosol and breaks glucose into two occurs in the cytosol and breaks glucose into two pyruvatespyruvates

- Krebs Cycle- Krebs Cycle takes place within the mitochondrial matrix, and breaks takes place within the mitochondrial matrix, and breaks

a pyruvate into a pyruvate into COCO2 2 and produce some ATP and NADand produce some ATP and NADHH. .

- Some steps of Glycolysis and Krebs Cycle are Redox in which- Some steps of Glycolysis and Krebs Cycle are Redox in which

dehydrogenase enzyme reduces NAD dehydrogenase enzyme reduces NAD++ into NAD into NADHH..

- - Electron Transport ChainElectron Transport Chain accepts accepts ee-- from from NADNADHH and passes these and passes these ee--

from one protein molecule to another.from one protein molecule to another.

- At the end of the chain, - At the end of the chain, ee-- combine with both combine with both HH++ and and OO22 to form to form HH22OO

and and release energyrelease energy..- These energy are used by mitochondria to synthesis 90% of the - These energy are used by mitochondria to synthesis 90% of the cellularcellular ATP ATP via via ATP-synthaseATP-synthase, a process called , a process called Oxidative PhosphorylationOxidative Phosphorylation, in, in the inner membrane of mitochondria. the inner membrane of mitochondria.

- Some of ATP is produced at these tow steps via (- Some of ATP is produced at these tow steps via (substrate-level-substrate-level- phosphorylation phosphorylation).).

Summary of cell respirationSummary of cell respiration

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DefinitionsDefinitions:: تعريفات

Chemiosmosis:Chemiosmosis: a process via which oxidative phosphorylationoxidative phosphorylation takes place at the end of the Electron Transport Chain to produce 90% of ATP via ATP-synthase.

Or, is the process in which ATP synthesis powered by the flow of H+ back across ATP synthase.

ATP-synthase:ATP-synthase: an enzyme presents in the inner mitochondrial

membrane and used in making ATP by using H+ (protons).

NADNAD++:: Nicotinamide adenine dinucleotide, which is a co-enzyme that helps electron transfer during redox reactions in cellular respiration.

FAD:FAD: Flavin adenine dinucleotide, which is an electron acceptor that helps electron transfer during Krebs Cycle and Electron Transport Chain in cellular respiration.

• Oxidation refers to the Oxidation refers to the loss of electronsloss of electrons to any electron acceptor, not to any electron acceptor, not just to oxygen.just to oxygen.– In glycolysis, glucose is oxidized to 2 pyruvate molecules with NADIn glycolysis, glucose is oxidized to 2 pyruvate molecules with NAD++ as as

the oxidizing agent (not Othe oxidizing agent (not O22).).– Some energy from this oxidation produce 2 ATP.Some energy from this oxidation produce 2 ATP.– If oxygen is present, additional ATP can be generated when NADH If oxygen is present, additional ATP can be generated when NADH

delivers its electrons to the electron transport chain.delivers its electrons to the electron transport chain.

• Glycolysis generates 2 ATP when oxygen is absent (anaerobic Glycolysis generates 2 ATP when oxygen is absent (anaerobic يالهوائ ).).

• Anaerobic catabolism of sugars can occur by Anaerobic catabolism of sugars can occur by fermentationfermentation..• FermentationFermentation can generate ATP from glucose by substrate-level can generate ATP from glucose by substrate-level

phosphorylation as long as there is a supply of NADphosphorylation as long as there is a supply of NAD++ ( (the oxidizing agent) to accept electrons.) to accept electrons.– If the NADIf the NAD++ pool is exhausted pool is exhausted إسـتُـنفِـذإسـتُـنفِـذ, glycolysis shuts down., glycolysis shuts down.– Under aerobic Under aerobic هوائىهوائى conditions, NADH transfers its electrons to the conditions, NADH transfers its electrons to the

electron transfer chain, recycling NADelectron transfer chain, recycling NAD++..

• Under anaerobic conditions, various fermentation pathways generate Under anaerobic conditions, various fermentation pathways generate ATP by glycolysis and recycle NADATP by glycolysis and recycle NAD++ by transferring electrons from by transferring electrons from NADH to pyruvate.NADH to pyruvate.

Fermentation: Fermentation: Enables م#ِك!ن$ some cells to يproduce ATP without the help of oxygen

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• Alcohol fermentation:Alcohol fermentation: the the pyruvatepyruvate is converted to is converted to ethanolethanol in two steps. in two steps.

– First, First, pyruvatepyruvate is converted to is converted to acetaldehydeacetaldehyde by the removal of CO by the removal of CO22. .

– Second, Second, acetaldehydeacetaldehyde is reduced by NADH is reduced by NADH to to ethanolethanol..

– Alcohol fermentation by Alcohol fermentation by yeastyeast is used in is used in winemaking.winemaking.

• Lactic acid fermentation:Lactic acid fermentation: the the pyruvatepyruvate is reduced directly by NADH to is reduced directly by NADH to form form lactatelactate (ionized form of lactic acid). (ionized form of lactic acid). – Lactic acid fermentation by some Lactic acid fermentation by some fungifungi and and

bacteriabacteria is used to is used to make make cheese and yogurtcheese and yogurt..

– Muscle cells switch from aerobic respiration Muscle cells switch from aerobic respiration to lactic acid to lactic acid fermentation to generate ATP fermentation to generate ATP when O when O22 is scarce is scarce نادرنادر..• The waste product, lactate, may cause The waste product, lactate, may cause

muscle fatigue, but ultimately it is muscle fatigue, but ultimately it is converted back to pyruvate in the liver.converted back to pyruvate in the liver.

ExamplesExamplesof of anaerobicanaerobic respiration respiration::

A)- During exercise our bodies require a lot of energyA)- During exercise our bodies require a lot of energy• The body can only supply a limited amount of oxygen for The body can only supply a limited amount of oxygen for

cellular respirationcellular respiration• Energy is not produced at the rate requiredEnergy is not produced at the rate required• Cells will use anaerobic respiration to release extra energyCells will use anaerobic respiration to release extra energy• This produces lactic acid (a waste product).This produces lactic acid (a waste product).

B)- We use yeast to make breadB)- We use yeast to make bread ●● COCO22 produced causes bread to rise by creating air pockets produced causes bread to rise by creating air pockets

●● The ethanol (alcohol) produced evaporated during bakingThe ethanol (alcohol) produced evaporated during baking

Summary of anaerobic respirationSummary of anaerobic respiration

Without oxygenWithout oxygen• Pyruvate remains in the cytoplasm (no link reaction, no Krebs Pyruvate remains in the cytoplasm (no link reaction, no Krebs

cycle).cycle).

• Pyruvate is converted into waste and removed from the cells.Pyruvate is converted into waste and removed from the cells.

• No ATP is produced (except from glycolysis).No ATP is produced (except from glycolysis).

• In humans the waste=lactate (lactic acid).In humans the waste=lactate (lactic acid).

• In yeast the waste=ethanol and COIn yeast the waste=ethanol and CO2.2.

• Once the pyruvate is converted into waste, the cells can go through Once the pyruvate is converted into waste, the cells can go through glycolysis again.glycolysis again.

• If pyruvate was not converted into waste the cells would not go If pyruvate was not converted into waste the cells would not go through glycolysis.through glycolysis.

• (Glycolysis produces pyruvate. If it is already present there is no (Glycolysis produces pyruvate. If it is already present there is no reason to make more.).reason to make more.).

Fat and Protein BreakdownFat and Protein Breakdown

A.A. FatsFats-have more energy per gram than carbohydrates or proteins (~2x as -have more energy per gram than carbohydrates or proteins (~2x as much)much)

-fatty acid chains are oxidized and broken into smaller 2 carbon -fatty acid chains are oxidized and broken into smaller 2 carbon chainschains

-the 2 carbon chains are converted into acetyl CoA to enter the -the 2 carbon chains are converted into acetyl CoA to enter the Kreb’s cycleKreb’s cycle

B. B. ProteinsProteins-must be converted into individual amino acids-must be converted into individual amino acids

-excess amino acids are converted by enzymes into intermediated -excess amino acids are converted by enzymes into intermediated of glycolysis and Krebs cycleof glycolysis and Krebs cycle

- amino acids go through deamination (amino groups are removed)- amino acids go through deamination (amino groups are removed)

-nitrogenous wastes from the amino groups are released as wastes-nitrogenous wastes from the amino groups are released as wastes

-new compounds enter glycolysis or Krebs-new compounds enter glycolysis or Krebs

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• Some organisms (Some organisms (facultative facultative anaerobes anaerobes اختياريا ,( ,(الالهوائيةincluding yeast and many bacteria, including yeast and many bacteria, can survive using either can survive using either fermentation or respiration.fermentation or respiration.

• At a cellular level, human muscle At a cellular level, human muscle cells can behave as facultative cells can behave as facultative anaerobes, but nerve cells cannot.anaerobes, but nerve cells cannot.

Proteins and fatsProteins and fats,, can also enter the can also enter the respiratory pathways, including respiratory pathways, including glycolysis and the Krebs cycle, like glycolysis and the Krebs cycle, like carbohydrates.carbohydrates.