46554804 IB Chem Biochemistry Energy and Respiration 6

7/29/2019 46554804 IB Chem Biochemistry Energy and Respiration 6

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Energy and Respiration

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Energy and foodThe amount of energy available from acertain food is sometimes called itscalorific value

The average adult requires about 8400Kilojoules (2000 kcal) of energy per day

An adult male undertaking heavy physicallabor may require as much as 14,700kilojoules (3500 kcal)

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Carbohydrates, proteins and fats make up most of the human diet. The idea ratio should be approximately 60% to 30% to 10%

respectively

Carbohydrates are the most readily available source of energy

Fats which are non-oxidized provide the most energy per mass


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Energy and food

The body does not burn food but

nevertheless it is converted to the

same set of products (CO2 and H2O)

through a series of oxidationreactions.

Since Hess law shows that the

energy change is independent of the

pathway, the same amount of energyis released through burningfood.

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The Bomb Calorimeter

The calorific value of acandy bar is about 250Dieticians Calories or 250kilocalories)

This means that if it were

burned in a calorimeter, theenergy produced oncombustion would raise thetemperature of 2.5 kg waterby 100C assuming that thecalorimeter itself does not

absorb any energy.In most cases the energyabsorbed by the calorimetercannot be ignored and mustbe included in the

calculations.

A diagram of a bomb calorimeter

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A bomb calorimeter is oftenused to measure theenergy content of food.

The calorific value of foodcan be measured by heating

a pre-measured mass offood and igniting it in anoxygen atmosphere.

The heat is transferred to awater system and the heatevolved is computed fromthe temperature change andthe mass of water


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The Bomb CalorimeterA large candy bar

weighs 50 g. If a 5.00 gsample of the candybar, on completecombustion raises thetemperature of 500 g

water in a glasscontainer by 59.6C.

Calculate the calorificvalue of the candy bar.

The heat capacity ofthe glass calorimeter is20.9 cal C-1


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A large candy bar weighs 50 g. If a 5.00 g sample of thecandy bar, on complete combustion raises thetemperature of 500 g water in a glass container by 59.6C,calculate the calorific value of the candy bar. The heatcapacity of the glass calorimeter is 20.9 cal C-1

Heat produced = heat absorbed by water + heat

absorbed by calorimeter

= (m x C x T)water+ (m x C. x T)calorimeter

= (500 g x 1.00 cal g-1

C-1

x 59.6 C) +(20.9 cal C-1 x 59.6C)

= 25086 calories

= 25.09 kcal (produced by 5.0 g of candy bar)

= 5.02 kcal g-1

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Respiration

Respiration is crucialfunction for all livingorganisms.

In general theprocess ofrespiration servestwo basic purposes1. The disposal of

electrons generatedduring catabolism

2. The production ofATP.

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Cellular Respiration

Cellular respiration

involves a set of metabolic

processes that occur in the

cell to convert biochemical

energy from nutrients intoadenosine triphosphate

(ATP) and waste products

Respiration involves

catabolic redoxreactions. One molecule

is oxidized and another is

reduced.

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Adenosine Triphosphate

The structure of ATP includes an adenine group, a

ribose sugar, and three phosphate groups


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Adenosine Triphosphate

Energy released from the catabolic destruction of

carbon containing molecules is stored in ATP.


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ATP and ADP

Energy is releasedwhen a phosphategroup is releasedfrom ATP resultingin the formation of

ADP. Thereversible reactionbetween ATP and

ADP acts much likea battery allowingthe cell to store andrelease energy

The conversion of ATP to ADP releases about 30.5 kJ mol-1


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Aerobic and Anaerobic Respiration

Respiration may be eitheraerobic or

anaerobic

Aerobic respiration uses oxygen as its

terminal electron acceptor,

Anaerobic respiration uses terminal

electron acceptors other than oxygen

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Aerobic Respiration

Aerobic respiration requires oxygen

A. It involves the break down of glucose, amino

acids and fatty acids to release energy

B. Oxygen is the terminal electron acceptor.

C. The overall process of aerobic respiration can

be described as:

Glucose + Oxygen Energy + Carbon dioxide +

Water

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Aerobic Respiration

The aerobic respiration is a high energy yieldingprocess.

Up to 38 molecules of ATP are produced for

every molecule of glucose that is utilized.Aerobic respiration takes place in almost allliving things.

It is easy to get rid of the Carbon Dioxide and

excess water; this is excretion (the removal ofthe toxic waste products of metabolism), andmaximum energy is released from the glucose.

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Anaerobic Respiration

Some organisms can respire in the absence of air: this isanaerobic respiration. This does not release so muchenergy and it produces more toxic waste products.

When Oxygen is not available, anaerobic respiration also

occurs in humans.Anaerobic respiration can take place during vigorousexercise, building up lactic acid in muscle tissue. Thisresults in muscle pain and cramping.

The bacteria in milk also produce lactic acid but is an opticalisomer of that produced in muscle cramping.

Yeasts produce alcohol which is also toxic. Eventually therewill be so much alcohol that the yeast cannot survive.

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Anaerobic respiration is a special type of respiration, whichtakes place without oxygen to produce energy in the form of

ATP or adenosine tri-phosphate.

The process of anaerobic respiration for production of

energy can occur in either of the ways represented below:

Glucose Energy (ATP) + Ethanol + Carbon dioxide (CO2)

Glucose Energy (ATP) + Lactic acid

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The process of anaerobic respiration isrelatively less energy yielding than aerobicrespiration

During the alcoholic fermentation or the

anaerobic respiration two molecules of ATP(energy) are produced. for every molecule ofglucose used in the reaction.

Likewise for lactate fermentation 2 molecules of

ATP are produced for every molecule ofglucose used.

Thus anaerobic respiration breaks down oneglucose molecule to obtain two units of the

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Hemoglobin and Oxygen Transport

The ability of iron to form complexes plays an important inthe transport of oxygen and carbon dioxide in thehemoglobin of the blood

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Hemoglobin is a complex protein. At certain sites within theprotein are structures known as porphyrin rings. A Fe2+ ionat the center of the ring attracts and transports oxygen

O2

At high oxygen

concentrations

(as in the lungs)

hemoglobin

binds to the

oxygen

molecules whichis then carried to

the cells.

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At high carbon dioxide concentrations as arefound at the cell level hemoglobin

CO2

binds to the

carbon dioxide

moleculeswhich are then

transported

back to the

lungs where the

carbon dioxide

is exhaled

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They attach to

the iron more orless

permanently,

rendering the

hemoglobinuseless

Species such as carbon monoxide and Cyanidepoison hemoglobin

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Electron Transport

The oxidation of food at thecellular level involves aseries of redox reactionsinvolving electron transport

These reactions take placein the mitochondria foundinside the cell

The enzymes that catalyzethese oxidation processes

are called cytochromesCytochromes incorporateporphyrin rings with either aCu2+ or Fe2+ at the center

+

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Electron Transport

The cytochrome structure heme group from cytochromeoxidase

+

Cytochromes contain Cu2+

or Fe3+ ions. The porphyrin

ligand contains 4 nitrogenatoms, each of which

donates 2 electrons.

During each step of theoxidation of glucose:

Fe3+ Fe2+ + e-

or

Cu2+ Cu+ + e-

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Electron Transport

The cytochrome structure heme group fromcytochrome oxidase.

+

Oxidation stage of glucose

C6H

12O

6+ 6H

2O 6CO

2+24H

++24e-

Fe3+ + e- Fe2+ (Metal ion is reduced)

Reduction stage

O2

+ 4H+ +4e- 2H2O

Fe2+ Fe3+ + e- (Metal ion is oxidized)

Cu+ Cu2+ + e-

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46554804 IB Chem Biochemistry Energy and Respiration 6

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