5. Cellular Respiration

7/27/2019 5. Cellular Respiration

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Lesson Objective: Describe aerobic and anaerobic respiration

and the requirement for such conditions.

TOPIC 5: CELLULAR RESPIRATION

There are 2 types of cell respiration, namely

a) Aerobic Respiration

Which requires O2, summarized by the

following equation:

C6H12O6 + 6O2 6CO2 + 6H2O + Energy

b) Anaerobic Respirationwhich does not require O2; the equations of

the reaction are different in plants & animals.

5.1 TYPES OF RESPIRATION


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In Plants

C6H12O6 2C2H2OH + 2CO2 + 2ATP

(ethanol)

In Animals

C6H1206 2CH3CH(OH)COOH + 2ATP

(lactic acid)


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Adenosinetriphosphate (ATP)is a nucleotide

molecule. It consists of a base

adenine, a pentosesugar ribose,

combined with threephosphate groups.

Adenosine triphosphate (ATP)


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Cellular respiration refers to a seriesof biochemical reactions that takeplace in the cells. This processinvolves the breakdown of organicmolecules to liberate energy (ATP).

DEFINITION


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Lesson Objective: Describe the importance of aerobic respiration

during oxidation of glucose which involve

glycolysis, Krebs cycle & electron transport chain.


There are 4 main stages in aerobic respiration;

i) Glycolysis

ii) Link Reaction

iii) The Krebs Cycle

iv) Electron Transport Chain

In eukaryotes, glycolysis occurs in the cytoplasm

The other processes take place in themitochondria.

5.2:Aerobic Respiration


8/58TOPIC 5: CELLULAR RESPIRATION


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Lesson Objective: Outline glycolysis from glucose to

pyruvate with the yield of ATP & reduced NAD+.


Glycolysis is the breakdown of the glucose

(6C) molecule in a number of enzyme-

controlled steps into 2 molecules of

pyruvate (3C).

The process takes place in the cytoplasm

of cells & does not require O2.

There is a net production of 2 ATP

molecules per molecule of glucose.

GLYCOLYSIS


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Lesson Objective: Show the steps where the energy,

ATP and NADH are produced.


STAGE 1

STAGE 2

STAGE 3(X 2)



An outline of the main stages of glycolysis

: Phosphorylation of Glucose

The glucose molecule is phosphorylated,

receives a high energy phosphate from ATP toincrease its energy level to become glucose-6-

phosphate.

Glucose glucose-6-phosphate

Stage 1

ATP ADP + Pi



2. Glucose-6-phosphate is rearranged to

become the isomer fructose-6-phosphate.

3. The frutose-6-phosphate is further

activated by the addition of another

phosphate group from ATP.

Fructose-6-phosphate fructose-1,6-

diphosphate

ATP ADP + Pi



:Breakdown of fructose diphosphate

The fructose-1,6-diphosphate produced is split(lysis) into gluceraldehyde-3-phosphate & itsisomer dihydroxyacetone phosphate.

Fructose-1,6-diphosphate G3P + DHAP

G3P DHAP

(3C) (3C)

DHAP rearranges into another molecule of G3P(2 molecules of G3P produced go throughidentical reaction).

Stage

2

Isomerase



:Oxidation of G3P

G3P is oxidised, hydrogen atoms are removed,

NAD+ is reduced to become NADH.

An inorganic phosphate (Pi) attached to

increase the energy of glycerate-1,3-

diphosphate.

One phosphate from each glycerate-1,3-diphosphate is transferred to ADP to form ATP.

Stage3



The 3-phosphoglycerate is rearranged to form 2-

phosphoglycerate. Removal of water produces phosphoenol-

pyruvate (PEP).

The 2nd phosphate is transferred to ADP form

ATP. Phosphoenol pyruvate is converted topyruvate (pyruvic acid).

A summary of ATP & NADH production duringglycolysis of a glucose molecule is

2 molecules of ATP (4-2 molecule

is that were used in stage 1.

2 molecules of NADH.


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Lesson Objective: Out line the link reaction to explain the

conversion of pyruvate to acetyl coenzyme A

(2C), before entering the Krebs cycle.


Aerobic respiration takes place when O2 isavailable.

Pyruvate easily enters the matrix of themitochondria.

Pyruvate (3C) formed at the end of glycolysis isdecarboxylated (removal of CO2) & is oxidised(the removal of hydrogen atoms) to form 2-carbon acetate (2C).

The acetate combines with coenzyme A (Co A)to form 2-carbon acetyl coenzyme A (Acetyl-Co

A) which then enters into the Krebs Cycle.

2. LINK REACTION



Link reaction



The process is called oxidativedecarboxylation or the link reaction as

it links glycolysis to Krebs Cycle.

There are 2 acetyl Co A molecules formedsince one glucose molecule produces 2

pyruvate molecules.

(The link reaction is sometimes includedas part of the Krebs Cycle).


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Lesson Objective: Outline the Krebs cycle occuring in the

mitochondrion, explaining that citrate is

reconverted to oxaloacetate in a series of reactions.


Acetyl Co A (2C) combines withoxaloacetate (4C) in acondensation reaction to formcitrate (6C). A coenzyme (Co A)

is released. Citrate rearranges by the

removal of a water molecule &the addition of water to form itsisomerisocitrate (6C).

Isocitrate is oxidised, yeilding apair of electrons that reduce amolecule of NAD+ to NADH.

3. KREBS CYCLE



Then the oxidised intermediate is

decarboxylated, yielding a five carbon molecule

called -ketoglutarate (5C).

Second oxidative-decarboxylation of-

ketoglutarate takes place. This producessuccinyl coenzyme A (4C), C02 & NADH.

Substrate level phosphorylation take place.

Succinyl Co A is converted to succinate (4C).

The energy released is used for phosphorylation

of GDP forming GTP. GTP transfer its

phosphate group to ADP forming ATP.

Lesson Objective: State the steps where the energy

and ATP, NADH and FADH2 are produced.



Succinate is oxidised to fumarate (4C), 2H

atoms are transferred to FAD to formFADH2.

Fumarate becomes hydrated by addition

of water is converted to malate (4C). Malate is oxidised regenerating

oxaloacetate (4C) & NAD+ is reduced toNADH.

Oxaloacetate can be used to combine withacetyl Co A & the cycle is repeated.


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Co A

(6C)

(6C)

(5C)

(4C)(4C)

(4C)

(4C)

(4C)

KREB

CYCLE


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Lesson Objective: Explain the processes involved in decarboxylation

and dehydrogenation and describe the role of

NAD+ and FAD.


In this cyclic process, decarboxylation takes

place twice, dehydrogenation takes place 4times & formation of GTP from ADP &phosphate once.

During the dehydrogenation process, 3 timesNAD+ & one time FAD are used as H acceptors

forming NADH + H+ & FADH2 respectively. From one Krebs Cycle; 3 NADH, one FADH2 &

one GTP are produced.

One glucose molecule produces 2 molecules of

acetyl coenzyme. The cycle is turned twice for each glucose

molecule broken down.


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Lesson Objective: Describe oxidative phosphorylation

occurring in the mitochondrion including the

role of oxygen.


The electron transport system is a chain of electronacceptor embedded in the inner membrane of themitochondrion.

High energy electron removed from respiratory

intermediates are carried by NADH & FADH2 to innermitochondrial membrane.

The folding of the inner membrane to form cristaeincreases its surface area, providing space forthousands of copies of the chain in each mitochondrion.

During electron transport along the chain, electroncarriers alternate between reduced and oxidized statesas they accept and donate electrons.

4. THE ELECTRON TRANSPORT CHAIN


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Complex I: NADH Dehydrogenase

( Flavoprotein).Complex I is responsible

for removing two electrons from NADH

and transferring them to the electron

carrier, ubiquinone (Coenzyme Q).

NADH dehydrogenase also moves four

protons from the mitochondrial matrix to

the intermembrane space, beginning theproduction of a proton gradient.


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Complex II: Succinate Dehydrogenase:Complex II removes electrons from succinateand transfers them to ubiquinone via FAD.Succinate dehydrogenase does not contribute tothe proton gradient.

Complex III: Cytochrome b-c Complex:Complex III removes two electrons formubiquinone and transfers them to two moleculesof the electron carrier, cytochrome c. The

cytochrome b-c complex also moves fourprotons across the inner mitochondrialmembrane, further contributing to the protongradient.


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Complex IV: Cytochrome Oxidase complex:

Complex IV removes two electrons from the twomolecules of cytochrome c and transfers them to

molecular oxygen (The final electron acceptor)

which combined with H+ ions to form water.

O2 + 2e- + 2H+ H2O

Cytochrome c oxidase also moves two electrons

across the inner mitochondrial membrane,

adding to the proton gradient.


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As they pass along the electron transport

chain, they lose much of their energy & theenergy released is used to synthesise

ATP.

Another source of electron for electrontransport chain is FADH2, the other

reduced product of the Krebs cycle.

FADH2 adds its electron to the electrontransport chain at a lower energy level

than NADH does (at ubiquinone).


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Consequently, the electron transport chain

provides less energy for ATP synthesis

when the electron donor is FADH2.

3 ATP molecules are produced for

every NADH that enters the electron

transport chain.

2 ATP molecules for every FADH2 that

enters the electron transport chain.


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Lesson Objective: Explain the chemiosmosis theory.


Electrons released by the oxidation ofsubstrate in the matrix flows down theelectron transport chain.

The energy released by the electrontransport chain is used to pump hydrogenions (H+) from the matrix into theintermembrane space. This builds up atransmembrane electro-chemical protons(H+) gradient.

Chemiosmosis Hyphothesis


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The inner mitochondrial membrane ispermeable to hydrogen ions.

The gradient forces hydrogen ions to

diffuse through the ATP synthetase (ATPsynthase) complex down itselectrochemical gradient. Their potentialenergy is used to synthesise ATP from

ADP & Pi. The process is calledchemiosmosis.


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Energy yield from the complete oxidation of glucose by

aerobic respiration


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The inner motochondrial membrane is not

permeable to NADH.

Therefore the NADH molecules produced in the

cytosol during glycolysis cannot diffuse into themitochondria to transfer their electrons to the

electron transport chain.

Unlike ATP & ADP, NADH does not have a

carrier protein to transport it across the

membrane.

Mitochondrial shuttle system


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In liver, kidney, & heart cells, a specialshuttle system transfers the electrons fromNADH through the inner mitochondrialmembrane to the NAD+ molecule in the

matrix. These electrons are transferred to the

electron transport chain in the innermitochondrial membrane, and up to threemolecules of ATP are produced per pair ofelectron.


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In skeletal muscle, brain & some other types ofcells, another type of shuttle operates.

Because this shuttle requires more energy thanthe shuttle in liver, kidney & heart cell, theelectron are at a lower energy level when they

enter the electron transport chain. They are accepted by ubiquinone rather than by

NAD+ & so generate a maximum of 2 ATPmolecules per pair of electrons.

This is why the number of ATPs produced byaerobic respiration of 1 molecule of glucose inskeletal muscle cells is 36 rather than 38.


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In the absence of O2, anaerobic

respiration occurs, for e.g:

a) in the several types of fungi, bacteria &earthworms living in muddy & O2

deficient conditions.

b) in skeletal muscles of vertebrates that

are contracting actively.

5.3: Anaerobic Respiration : Fermentation &

Application


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Organisms that obtain energy from the

breakdown of sugar through anaerobicrespiration are known as anaerobes.

During anaerobic respiration, glucose only

breaks down into pyruvic acid when undergoingglycolysis. The pyruvic acid formed is not

converted into acetyl Co A for entry into Krebs

cycle as in aerobic respiration.

Instead, the pyruvic acid is converted intoethanol or lactic acid.


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Lesson Objective: Explain what is meant by fermentation

Describe alcohol and lactate fermentation


Anaerobic mechanisms of energy production

which do not involved the respiratory chain or

cytochromes are called fermentation

Fermentation coverts glucose into lactic acid(lactate) in animal cells (Lactate fermentation)

Fermentation converts glucose into ethanol &

CO2 in plant cells, fungi cells (eg; yeast ) &

bacteria (Alcohol fermentation).

Fermentation


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Occurs in certain fungi, bacteria &

during strenuous activity in

muscle cells of humans & other

complex animal. In this alternative pathway, NADH

produced during glycolysis

transfers hydrogen atoms to

pyruvate, reducing it to formlactate & NAD+ is regenerated.

Lactate (lactic acid ) Fermentation


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If the amount of O2 delivered to muscle cells is

insufficient to support aerobic respiration, the

cells shift briefly to lactate fermentation.

Lactate accumulation in the muscle causesfatigue & muscle cramps. The O2 that is required

to break down the lactate is known as the

oxygen debt & is repaid by deep & rapid

breathing at the end of strenuous activity.


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The lactate formed is removed to other tissues

and dealt with by one of two mechanisms : it is converted back to pyruvate The pyruvate then

proceeds to be further oxidised, finally producing alarge amount of ATP.

it is converted back to glucose in the liver

The process of conversion of lactate to glucoseis called gluconeogenesis, uses some of the

reactions of glycolysis (but in the reversedirection) and some reactions unique to thispathway to re-synthesise glucose.


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Lesson Objective:



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E.g: Yeast carried out alcohol fermentationwhen deprived of O2.

They have enzymes that decarboxylate

pyruvate, releasing CO2& forming a two-carbon compound called acetaldehyde.

NADH produced during glycolysis

transfers hydrogen atoms to acetaldehyde,reducing it to form ethyl alcohol (ethanol)& NAD+ regenerated to be reused.

Alcohol Fermentation


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Both alcohol fermentation & lactatefermentation are highly inefficient becausethe fuel is only partially oxidised.

This is because a considerable quantity of

energy still remains trapped in the ethanolor lactic acid molecules.

A net profit of only 2ATPs is produced by

the fermentation of one molecules ofglucose, compared with up to 36-38ATPswhen O2 is available.

L Obj i Di h i f


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Lesson Objective: Discuss the importance of

fermentation in industry.


a) In the process of baking cakes &bread

In this process, the flour dough ismixed with yeast.

The CO2 gas produced from thefermentation process causes the

dough to rise & give soft cake orbread texture when it is baked inthe oven.

Importance of Fermentation in

Industry. Yeast


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b) In the process of beer & wine manufacture

During the manufacture ofbeer, the enzyme(diastase) in the malt, rice or corn convertthe starch in the cereal into maltose.

The yeast mixture is then added to allowfermentation to take place.

During fermentation, the enzyme maltaseconverts maltose into glucose.

Glucose is then converted by the enzyme

zymase into ethanol & CO2.Wine is made by the fermentation of yeaston grape or other fruit sugars.


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c) In the process of making Cheese &

Yoghurt (Dairy Industry).

Cheese is made from milk.

Several type of bacteria &fungi are used to form

different type of cheese

through lactatefermentation.
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Yoghurt is made of concentrated milk.

Lactose in the milk is fermented to lactic acid by

lactic acid bacteria,

e.g; Lactobacillus bulgaricus.

Lactic acid gives the yoghurt its flavour (sourtaste).

Lactobacillus


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Tempeis one of the most

popular fermented foods

in Indonesia, Malaysia and

Singapore. It is traditionally prepared with soy beans or a

certain variety of peanut fermented with mold,Rhizopus spp.

The cultured soybeans or nuts are boundtogether by a thick white mycelium of new mold-growth, to form a cake.

Local fermented foods


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Another examples of local fermented

foods are tapai, dadih, budu and cincalok.

Ragi(yeast cake) is used by crushing it,

and then mixing the powder with cooked,

cooled ingredients such as glutinous rice(fortapai making).

The mixture is fermented for a particular

length of time, depending on the productbeing prepared.


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Lesson Objective: Briefly describe how protein is

oxidised through transamination


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oxidised through transamination

and deamination.


Each gram of lipid contains 9 kcal (38kJ), morethan twice as much energy as 1 g of glucose oramino acid, which have about 4kcal (17kJ) pergram.

The oxidation of amino acidWhen carbohydrate & lipid reserve have beenexhausted, amino acid derived from proteindigestion are also can used as fuel molecules.

Amino acids are transformed into one of themetabolic intermediates that are fed intoglycolysis or the Krebs cycle.


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Proteins first hydrolysed into their monomers amino

acids & deaminated (their amino group{-NH2} are removed).

The amino group is converted to urea & excreted.

The carbon chain is metabolised & eventually is used as

a reactant in one of the steps of respiration. The aminoacid alanine, for eg., undergoes deamination to becomepyruvate, the amino acid glutamate is converted to -ketoglutarate & the amino acid aspartate yieldsoxaloacetate.

Pyruvate enters aerobic respiration as the end product ofglycolysis, & -ketoglutarate & oxaloacetate both enteraerobic respiration as intermediates in the Krebs Cycle.


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5. Cellular Respiration