The Chemistry of The Chemistry of RespirationRespiration

The Chemistry of RespirationThe Chemistry of RespirationRespirationRespiration is the process by which is the process by which

chemical energy is released from food by chemical energy is released from food by oxidisationoxidisation. It occurs in every living cell . It occurs in every living cell and involves the regeneration of ATP by a and involves the regeneration of ATP by a series of reactions.series of reactions.

MetabolismMetabolism is the sum of all chemical is the sum of all chemical processes that occur in an organism. processes that occur in an organism. Respiration is an example of a metabolic Respiration is an example of a metabolic pathway.pathway.

GlycolysisGlycolysisThe process of cell respiration begins The process of cell respiration begins

with a with a 6-carbon6-carbon molecule of molecule of glucoseglucose being broken down by a being broken down by a series of enzyme-controlled steps to series of enzyme-controlled steps to form two form two 3-carbon 3-carbon molecules of molecules of pyruvic acidpyruvic acid

Glycolysis

GlycolysisThis process ofThis process of “glucose-splitting” “glucose-splitting”

requires energy from two molecules requires energy from two molecules of ATP to trigger it off but later in the of ATP to trigger it off but later in the process sufficient energy is released process sufficient energy is released to form 4 molecules of ATP giving a to form 4 molecules of ATP giving a net gainnet gain of two molecules of ATP of two molecules of ATP

Glycolysis occurs in the Glycolysis occurs in the cytoplasmcytoplasm

Glycolysis

The hydrogen acceptorThe hydrogen acceptorDuring glycolysis, hydrogen released During glycolysis, hydrogen released

becomes temporarily bound to a becomes temporarily bound to a coenzyme molecule coenzyme molecule which acts as which acts as a hydrogen acceptor and carrier.a hydrogen acceptor and carrier.

This coenzyme is called This coenzyme is called NADNAD(nicotinamide adenine dinucleotide).(nicotinamide adenine dinucleotide).

In its In its reducedreduced state the coenzyme is state the coenzyme is called called NADHNADH22

The fate of Pyruvic acidThe fate of Pyruvic acidPyruvic acid produced during glycolysis Pyruvic acid produced during glycolysis

diffuses into the central matrix of the diffuses into the central matrix of the mitochondrion where it is converted mitochondrion where it is converted into a into a 2-carbon compound 2-carbon compound called called Acetyl Co-AAcetyl Co-A..

This reaction is accompanied by the This reaction is accompanied by the release of hydrogen which again release of hydrogen which again becomes bound to becomes bound to NAD NAD to form to form NADHNADH22

Anaerobic respiration if oxygen absent

The Krebs’ CycleThe Krebs’ CycleThis is the This is the aerobicaerobic phase of respiration phase of respiration

and occurs in the and occurs in the matrixmatrix of the of the mitochondria. It is also known as the mitochondria. It is also known as the Citric Acid Cyle or the Tricarboxylic Citric Acid Cyle or the Tricarboxylic acid Cycle.acid Cycle.

Each molecule of Each molecule of Acetyl CoAAcetyl CoA resulting resulting from glycolysis reacts with a from glycolysis reacts with a 4-carbon4-carbon compound to form compound to form 6-carbon citric 6-carbon citric acidacid..

Citric acid is gradually converted back Citric acid is gradually converted back to the 4-carbon compound by a cyclic to the 4-carbon compound by a cyclic series of enzyme-controlled reactions series of enzyme-controlled reactions which result in the removal of carbon which result in the removal of carbon and hydrogen from the intermediate and hydrogen from the intermediate carbon compounds.carbon compounds.

Using page 25 of Torrance, draw out Using page 25 of Torrance, draw out a diagram combining glycolysis and a diagram combining glycolysis and the Krebs cycle showing the names the Krebs cycle showing the names and number of carbon atoms in each and number of carbon atoms in each intermediateintermediateAnswer “Testing Your Knowledge” Answer “Testing Your Knowledge” questions 1 and 2 on page 26questions 1 and 2 on page 26Answer “Testing Your Knowledge” Answer “Testing Your Knowledge” questions 1 and 2 on page 27questions 1 and 2 on page 27

The Cytochrome SystemThe Cytochrome System

In glycolysis and the Krebs’ cycle, In glycolysis and the Krebs’ cycle, there are six points at which there are six points at which hydrogen is released and bound to hydrogen is released and bound to NAD to form NADHNAD to form NADH22..

NADHNADH22 transfers the hydrogen to the transfers the hydrogen to the cytochrome systemcytochrome system in the in the christaechristae of the mitochondria of the mitochondria

Transfer of each molecule of hydrogen Transfer of each molecule of hydrogen along the cytochrome system by along the cytochrome system by NADHNADH22 releases sufficient energy to releases sufficient energy to produce three ATP.produce three ATP.

This process is called This process is called oxidative oxidative phosphorylationphosphorylation

The complete oxidation of one molecule of The complete oxidation of one molecule of glucose yields a total of glucose yields a total of

38 ATP38 ATP

i.e.i.e. 2 ATP 2 ATP from from glycolysisglycolysis,,36 ATP36 ATP from from oxidative phosphorylation oxidative phosphorylation

The cytochrome system, therefore, The cytochrome system, therefore, produces most ATP (requires produces most ATP (requires aerobicaerobic

conditions)conditions)

The final hydrogen acceptor in the The final hydrogen acceptor in the cytochrome system is cytochrome system is oxygenoxygen (forming (forming waterwater))

Alternative respiratory substratesAlternative respiratory substratesFatty acidsFatty acids are converted to Acetyl CoA in are converted to Acetyl CoA in

the matrix which enters the Krebs’ Cycle the matrix which enters the Krebs’ Cycle to produce ATP as above. Fat produces to produce ATP as above. Fat produces double the energy of the same mass of double the energy of the same mass of carbohydrate.carbohydrate.

Amino acidsAmino acids can also act as respiratory can also act as respiratory substrates and some of the body’s energy substrates and some of the body’s energy is always derived from excess dietary is always derived from excess dietary protein. Tissue protein may be broken protein. Tissue protein may be broken down during extreme and prolonged down during extreme and prolonged starvation.starvation.

SummarySummary

Copy and complete table 4.1 on page Copy and complete table 4.1 on page 30 of Torrance30 of Torrance

Measuring the rate of respirationMeasuring the rate of respirationMake notes on the set-up, design Make notes on the set-up, design features and precautions for a features and precautions for a respirometer from pages 28 and 29 respirometer from pages 28 and 29 of Torranceof TorranceUnder the heading “Applying your Under the heading “Applying your Knowledge” answer question 5 page Knowledge” answer question 5 page 31 Torrance31 Torrance

Anaerobic respirationAnaerobic respirationResults in a Results in a littlelittle energy from the energy from the

partial breakdownpartial breakdown of sugar in the of sugar in the absence of oxygen. Only glycolysis absence of oxygen. Only glycolysis can occur therefore only 2 molecules can occur therefore only 2 molecules of ATP are producedof ATP are produced

Anaerobic respiration in plants:Anaerobic respiration in plants:

Anaerobic respiration in animals:Anaerobic respiration in animals: