Cell Cell RespirationRespiration

Topics 3.7 & 8.1Topics 3.7 & 8.1

Definition of cell respirationDefinition of cell respiration

Cell respiration is the controlled Cell respiration is the controlled release of energy from organic release of energy from organic compounds in cells to form ATP.compounds in cells to form ATP.

It takes place in ALL cells – It takes place in ALL cells – prokaryotic and eukaryotic.prokaryotic and eukaryotic.

It can be It can be aerobicaerobic (involving oxygen) (involving oxygen) or or anaerobicanaerobic (no oxygen). (no oxygen).

Anaerobic RespirationAnaerobic Respiration

The process of respiration takes places The process of respiration takes places in several steps (metabolic pathway).in several steps (metabolic pathway).

Anaerobic respiration occurs in the Anaerobic respiration occurs in the CYTOPLASM.CYTOPLASM.

Glucose is broken down into a simpler Glucose is broken down into a simpler substance called PYRUVATE. (pyruvic substance called PYRUVATE. (pyruvic acid)acid)

A small amount of ATP is produced in A small amount of ATP is produced in this reaction.this reaction.

Anaerobic respiration contd.Anaerobic respiration contd.

If no OIf no O22 is available, the pyruvate is is available, the pyruvate is converted into waste products that converted into waste products that are later removed from the cell.are later removed from the cell.

In humans the waste product is In humans the waste product is LACTATE (lactic acid).LACTATE (lactic acid).

In yeast the waste products are In yeast the waste products are ETHANOL and CARBON DIOXIDE.ETHANOL and CARBON DIOXIDE.

No further ATP is made.No further ATP is made.

Anaerobic respiration contd.Anaerobic respiration contd.

Glucose Pyruvate LactateIn humans

Small yield of ATP

Glucose Pyruvate Ethanol + CO2

In yeast

Small yield of ATP

GLYCOLYSIS

GLYCOLYSIS

Aerobic respirationAerobic respiration

If OIf O22 is available, the pyruvate enters is available, the pyruvate enters the mitochondria where it is broken the mitochondria where it is broken down into COdown into CO22 and water. and water.

A large amount of ATP is produced in A large amount of ATP is produced in these reactions.these reactions.

Pyruvate

COCO2 2 + H+ H22OO

Large Large yield of yield of ATPATP

Oxidation & ReductionOxidation & Reduction

OxidationOxidation ReductionReduction

Involves Involves lossloss of of electronselectrons

Involves Involves gaingain of of electronselectrons

Addition of oxygenAddition of oxygen Removal of oxygenRemoval of oxygen

Removal of hydrogenRemoval of hydrogen Addition of hydrogenAddition of hydrogen

Oxidation & Reduction in Cell Oxidation & Reduction in Cell RespirationRespiration

Cell respiration involves several Cell respiration involves several redox reactions.redox reactions.

Hydrogen carriers accept hydrogen Hydrogen carriers accept hydrogen atoms removed from substrates.atoms removed from substrates.

NADNAD++ + 2H NADH + + 2H NADH + HH++

GlycolysisGlycolysis

First step in both aerobic and First step in both aerobic and anaerobic respiration.anaerobic respiration.

Occurs in cytoplasm.Occurs in cytoplasm. Four steps:-Four steps:-1.1. PhosphorylationPhosphorylation – 2 phosphates are – 2 phosphates are

added to glucose to form hexose added to glucose to form hexose biphosphate. 2ATPs provide the biphosphate. 2ATPs provide the phosphates and the resulting phosphates and the resulting molecule now has a higher energy molecule now has a higher energy level.level.

Glycolysis contd.Glycolysis contd.

2.2. LysisLysis – hexose biphosphate splits – hexose biphosphate splits into 2 molecules of triose phosphate.into 2 molecules of triose phosphate.

3.3. OxidationOxidation – 2 hydrogen atoms – 2 hydrogen atoms removed from each triose phosphate removed from each triose phosphate and collected by NADand collected by NAD++..

4.4. ATP formationATP formation – Pyruvate is formed – Pyruvate is formed by removal of 2 phosphates that are by removal of 2 phosphates that are joined to ADP to make ATP.joined to ADP to make ATP.

Glycolysis diagramGlycolysis diagramGlucoseGlucose

SummarySummary One glucose is One glucose is

converted into 2 converted into 2 pyruvatespyruvates

2 NAD2 NAD++ are are converted into 2 converted into 2 NADH + HNADH + H++

2 ATP molecules 2 ATP molecules used per glucose but used per glucose but 4 are produced 4 are produced giving a net yield of giving a net yield of 2 ATP.2 ATP.

Hexose Hexose biphosphatebiphosphate

2 triose 2 triose phosphatesphosphates

2 pyruvates2 pyruvates

PHOSPHORYLATION

LYSIS

OXIDATION

ATP FORMATION

2 ATP

2 ADP

2 NAD+

2 NADH + H+

4 ADP

4 ATP

Structure of mitochondriaStructure of mitochondria

Aerobic respiration – link Aerobic respiration – link reactionreaction

Pyruvate from glycolysis is absorbed by Pyruvate from glycolysis is absorbed by the mitochondrion.the mitochondrion.

The pyruvate is both OXIDIZED and The pyruvate is both OXIDIZED and DECARBOXYLATED.DECARBOXYLATED.

Enzymes in the matrix of the Enzymes in the matrix of the mitochondrion are responsible for each mitochondrion are responsible for each process.process.

The hydrogen that is removed is accepted The hydrogen that is removed is accepted by NADby NAD++ to form NADH + H to form NADH + H++..

The decarboxylated pyruvate is a 2-carbon The decarboxylated pyruvate is a 2-carbon compound (acetyl group) that reacts with compound (acetyl group) that reacts with coenzyme A.coenzyme A.

Summary of the link Summary of the link reactionreaction

PyruvatePyruvate acetyl acetyl CoACoA

Coenzyme A CO2

DECARBOXYLATION

OXIDATION

NAD+ NADH + H+

Aerobic respiration – Kreb’s Aerobic respiration – Kreb’s CycleCycle

An acetyl group (CHAn acetyl group (CH33CO) is CO) is transferred from acetyl CoA to a 4-transferred from acetyl CoA to a 4-carbon compound (oxaloacetate).carbon compound (oxaloacetate).

This results in the production of a 6-This results in the production of a 6-carbon compound (citrate).carbon compound (citrate).

Citrate is converted back into Citrate is converted back into oxaloacetate by a series of reactions oxaloacetate by a series of reactions involving involving DECARBOXYLATION, DECARBOXYLATION, OXIDATION OXIDATION andand PHOSPHORYLATION. PHOSPHORYLATION.

Kreb’s cycle contd.Kreb’s cycle contd. COCO22 is removed in 2 of the reactions as a is removed in 2 of the reactions as a

waste product and excreted together with waste product and excreted together with COCO22 from the link reaction. from the link reaction.

Hydrogen is removed in 4 of the reactions. Hydrogen is removed in 4 of the reactions. The hydrogens are picked up by carriers The hydrogens are picked up by carriers (NAD+ and FAD). (NAD+ and FAD).

These oxidations release energy which is These oxidations release energy which is stored by the carriers when they accept stored by the carriers when they accept hydrogen.hydrogen.

This energy is later released by the electron This energy is later released by the electron transport chain and used to make ATP.transport chain and used to make ATP.

ATP is produced directly in one of the ATP is produced directly in one of the reactions.reactions.

Summary of the Kreb’s Summary of the Kreb’s cyclecycle

oxaloacetate (C4)

citrate (C6)

C4

C5

CoAacetyl CoA

NAD+

NADH + H+

CO2

NAD+

NADH + H +

CO2

NADH + H+

NAD+

FADH2

FAD

ATP ADP

The electron transport chainThe electron transport chain

The electron transport chain (ETC) is The electron transport chain (ETC) is a series of electron carriers, located a series of electron carriers, located in the inner membrane of the in the inner membrane of the mitochondrion.mitochondrion.

NADH supplies 2 electrons (e-) to the NADH supplies 2 electrons (e-) to the first carrier.first carrier.

These e- pass along the chain, giving These e- pass along the chain, giving up energy at each stage.up energy at each stage.

The electron transport chain The electron transport chain contd.contd.

At 3 points along the chain enough At 3 points along the chain enough energy is given up for ATP to be made energy is given up for ATP to be made by the enzyme ATP synthetase.by the enzyme ATP synthetase.

This process is called OXIDATIVE This process is called OXIDATIVE PHOSPHORYLATION.PHOSPHORYLATION.

FADHFADH22 also feeds e- into the ETC, but also feeds e- into the ETC, but at a later stage than NADH, resulting at a later stage than NADH, resulting in 2 ATP molecules instead of 3.in 2 ATP molecules instead of 3.

ADPADP ATPATP

ADPADP ATPATP

ADPADP ATPATP

Summary of ETCSummary of ETC

The final recipient The final recipient of these e- is of these e- is oxygen.oxygen.

Oxygen is reduced Oxygen is reduced to form water.to form water.

This is the only This is the only stage of cellular stage of cellular respiration that respiration that uses oxygen.uses oxygen.

FADH FAD

NADNADH

Reduced cytochromes

Oxidized cytochromes

Oxidized cytochrome oxidase

Reduced cytochrome oxidase

O2H2O

ChemiosmosisChemiosmosis

The energy released as e- pass along the The energy released as e- pass along the ETC is used to pump protons (HETC is used to pump protons (H++ ions) ions) from the matrix into the intermembrane from the matrix into the intermembrane space.space.

Due to the small volume of this space, it Due to the small volume of this space, it quickly becomes concentrated with quickly becomes concentrated with protons. protons.

This creates 2 areas with different proton This creates 2 areas with different proton concentrations – LOW in matrix, HIGH in concentrations – LOW in matrix, HIGH in intermembrane space.intermembrane space.

Chemiosmosis contd.Chemiosmosis contd.

Protons move down the concentration Protons move down the concentration gradient by passing through channels gradient by passing through channels provided by the enzyme ATP synthase, provided by the enzyme ATP synthase, found in the inner membrane.found in the inner membrane.

When the ATP synthase enzyme is When the ATP synthase enzyme is activated, ADP is phosphorylated into activated, ADP is phosphorylated into ATP.ATP.

The coupling of ATP synthesis to electron The coupling of ATP synthesis to electron transport is called CHEMIOSMOSIS.transport is called CHEMIOSMOSIS.

Relationship between structure Relationship between structure & function of mitochondria& function of mitochondria

CristaeCristae – foldings of the inner membrane – foldings of the inner membrane that increase the surface area for the that increase the surface area for the electron transport chain and oxidative electron transport chain and oxidative phosphorylation.phosphorylation.

Fluid matrixFluid matrix – contains enzymes for link – contains enzymes for link reaction and Kreb’s cycle.reaction and Kreb’s cycle.

Intermembrane spaceIntermembrane space – the space – the space between inner and outer membranes is between inner and outer membranes is small to allow for accumulation of protons small to allow for accumulation of protons for chemiosmosis.for chemiosmosis.

The EndThe End

Now all you have to do is…..Now all you have to do is…..

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