CHAPTER 5: CELLULAR RESPIRATION AND FERMENTATION

Biology Students’ Companion Resources SB025

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CHAPTER 5: CELLULAR RESPIRATION AND

FERMENTATION

SUBTOPIC : 5.1 Aerobic respiration

LEARNING OUTCOMES: (a) State the needs for energy and the role of respiration in living organisms.

(b) Outline the complete oxidation of glucose which involves glycolysis, Krebs

cycle and oxidative phosphorylation.

MAIN IDEAS

/KEY POINT EXPLANATION NOTES

Cellular

Respiration

• The catabolic pathway of aerobic and anaerobic respiration,

which break down organic molecules and use an electron

transport chain for the production of ATP.

Aerobic

respiration

• A catabolic pathway for organic molecules (glucose)

• Using oxygen as the final electron acceptor in an electron

transport chain and producing ATP.

Needs for energy

and the role of

respiration in

living organisms

• Most of the processes taking place in cells need energy to

make them happen.

• Examples of energy consuming processes in living

organisms are:

a) The contraction of muscle cells – to create movement

of the organism, or peristalsis.

b) Building up proteins from amino acids

c) The process of cell division to create more cells, or

replace damaged or worn out cells, or to make

reproductive cells

d) The process of active transport, involving the

movement of molecules across a cell membrane against

a concentration gradient

e) The conduction of electrical impulses by nerve cells


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MAIN IDEAS


• The Adenosine triphosphate (ATP) molecule is the "molecular

currency" of intracellular energy transfer.

• ATP is produced by:

a) Substrate-level phosphorylation

b) Oxidative phosphorylation

Substrate-level phosphorylation

• The enzyme-catalyzed formation of ATP

• By direct transfer of a phosphate group to ADP from an

intermediate substrate in catabolism

Oxidative phosphorylation

• The production of ATP using energy derived from the redox

reactions of electron transport chain.

• Generates most of ATP (90%).

Complete oxidation of glucose involves:

1. Glycolysis (in cytoplasm)

2. Krebs Cycle (in the matrix of mitochondrion)

3. Oxidative Phosphorylation : electron transport chain and

chemiosmosis (at cristae/inner membrane of

mitochondrion)

Complete

oxidation of

glucose

Complete oxidation of glucose

Complete oxidation of glucose

Link

reaction Kreb

cycle


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SUBTOPIC : 5.1.1 Glycolysis

LEARNING OUTCOMES: (a) Ilustrate to explain glycolysis pathway: (from glucose to pyruvate).

(b) Describe link reaction: (conversion of pyruvate to acetyl coenzyme A).

MAIN IDEAS


Glycolysis

• In the cytoplasm

• Glycolysis means “sugar splitting”. Break down glucose

(6C) into TWO molecules of pyruvate (3C).

• Occurs with or without O2 .

• Has two major phases:

a) Energy investment phase

o 2 ATP used

o Phosphorylate Sugar

b) Energy payoff phase

o 4 ATP yielded

• Net ATP yield : 2 ATP

• Produces : 2 NADH + 2H+

• No carbon is released as CO2

Glycolysis

pathway

Energy investment phase

- 2 ATP used

- involves 5 steps which are:

1. Glucose undergoes phosphorylation to become glucose-

6-phosphate • Catalysed by Hexokinase. • ATP is used.

2. Glucose 6-phosphate is converted to its isomer, fructose

6-phosphate

3. Fructose 6-phosphate undergoes phosphorylation to

become fructose 1,6-bisphosphate.

• Catalysed by Phosphofructokinase.

• ATP is used.

4. Fructose 1,6-bisphosphate split into dihydroxyacetone

phosphate (DHAP) & glyceraldehyde 3-phosphate (G3P)

5. Dihydroxyacetone phosphate (DHAP) is converted into

glyceraldehyde 3-phosphate (G3P).


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MAIN IDEAS


GLYCOLYSIS


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MAIN

IDEAS /KEY

POINT

EXPLANATION NOTES

Glycolysis

pathway

Energy payoff phase

- 4 ATP yield

- involves 5 steps:

6. Glyceraldehyde 3-phosphate is oxidized and undergoes

phosphorylation to become 1,3-bisphosphoglycerate.

• NADH is produced.

7. Phosphate group of 1,3-bisphosphoglycerate is removed to

become 3-phosphoglycerate.

• ATP is produced by substrate-level phosphorylation.

8. Phosphate group of 3-phosphoglycerate is relocated to

become 2-phosphoglycerate.

9. Water is removed from 2-phosphoglycerate to become

phosphoenolpyruvate (PEP).

10. Phosphate group of phosphoenolpyruvate is removed to

become pyruvate.

• ATP is produced by substrate-level phosphorylation.

Summary of

glycolysis


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MAIN IDEAS


LINK

REACTION

• In the presence of O2.

• Pyruvate enters the mitochondrion by active transport.

• Occur TWICE per glucose molecule.

• Because 2 pyruvate produced from one molecule of glucose

(Glycolysis).

• This step, linking the glycolysis and the citric acid cycle

catalyses three reactions:

1. Oxidative decarboxylation

• Pyruvate (3C) undergoes oxidative decarboxylation to

produce 2C sugar

• CO2 is released

2. NADH is produced

3. Coenzyme A (CoA) attaches on 2C sugar to form Acetyl

CoA.


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SUBTOPIC : 5.1.2 Krebs cycle

LEARNING OUTCOMES: (a) Illustrate to explain Krebs cycle: (oxaloacetate – citrate - isocitrate – α-

ketoglutarate - succinyl CoA -succinate - fumarate - malate).

MAIN IDEAS


Stage 2:

Krebs cycle

- Also known as Citric acid cycle

- Oxidize acetyl CoA to carbon dioxide

- Occur in mitochondrial matrix of eukaryotic cells or in the cytosol

of prokaryotes.

- Every acetyl CoA generate 1 ATP, 3 NADH and 1 FADH2

- NADH and FADH2 produced relay electrons to the electron

transport chain.

Explanation : 8 steps of the Kreb cycle :

1. Acetyl CoA (from oxidation of pyruvate) adds its two-carbon

acetyl group (2C) to oxaloacetate (4C), producing citrate (6C).

2. Citrate (6C) is converted to its isomer, isocitrate (6C), by removal

of one water molecule and addition of another.

3. Process : Oxidative decarboxylation

- Isocitrate (6C) is oxidized and undergoes decarboxylation to

become α-ketoglutarate (5C).

- NADH + H+ and CO2 are produced.

4. Process : Oxidative decarboxylation

- α-ketoglutarate (5C) is oxidized, undergoes decarboxylation and

attached to coenzyme A(CoA) to become succinyl CoA.

- NADH + H+ is produced.

- CO2 is produced.

5. CoA of succinyl CoA is displaced by a phosphate group, which is

then transferred to GDP forming GTP then transferred to ADP

forming ATP. Succinate (4C) is produced.

- ATP is produced by substrate-level phosphorylation

6. Succinate (4C) is oxidized to become fumarate (4C).

- FADH2 is produced.

7. Water is added to fumarate (4C), to produce malate (4C).

8. Malate (4C) is oxidized to produce oxaloacetate (4C).

- NADH + H+ is produced.

- Summary of products:

One turn of cycle

(1 molecule of pyruvate)

Twice turn of cycle

(1 molecule of glucose)

❖ 2 CO2.

❖ 3 (NADH + H+)

❖ 1 FADH2

❖ 1 ATP by Substrate Level

Phosphorylation

❖ 4 CO2.

❖ 6 (NADH + H+)

❖ 2 FADH2

❖ 2 ATP by Substrate Level

Phosphorylation


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MAIN IDEAS


1

8

7

6

5

4

3

2

KREB CYCLE

H2O


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SUBTOPIC : 5.1.3 Oxidative Phosphorylation: Electron Transport Chain and Chemiosmosis

LEARNING OUTCOMES: (a) Illustrate to explain electron transport chain: The pathway of electron transport is

NADH dehydrogenase, Ubiquinone /CoQ, cyt c reductase, cyt c, cyt c oxidase.

(b) explain chemiosmosis : proton motive force.

(c) explain complete oxidation of one molecule of glucose in active cells to produce

38 ATP

MAIN IDEAS


Oxidative

Phosphorylation

▪ The formation of ATP using energy derived from redox

reactions of an electron transport chain.

▪ Involve the electron transport chain and chemiosmosis

The component of electron transport chain and chemiosmosis

Electron

Transport Chain

(ETC)

▪ A sequence of electron carrier molecules (membrane proteins)

that shuttle electrons down a series of redox reactions that

release energy used to make ATP.

▪ The NADH and FADH2 molecules formed during the first three

stages of aerobic respiration each contain a pair of electrons that

were gained when the electron carrier NAD+ and FAD were

reduced.

▪ The NADH molecules carry their electrons to the inner

mitochondrial membrane, where they transfer the electrons to a

series of membrane-associated proteins collectively called the

electron transport chain.


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MAIN IDEAS


▪ NADH and FADH2 donate electrons to the electron transport

chain, which powers ATP synthesis via oxidative

phosphorylation.

▪ The electron transport chain is at the cristae of the

mitochondrion. The components are proteins complexes.

▪ The carriers are reduced (accept electrons) and oxidized

(donate electrons).

▪ Oxygen atom is the last electron acceptor, reacts with proton, to

form water.

Electron carrier in Electron Transport Chain:

Electron Carrier Function

NADH

dehydrogenase

Transfer electron from NADH to

coenzyme Q.

Pump proton into the intermembrane space

Succinate

dehydrogenase

Transfer electron from FADH2 to

ubiquinone (coenzyme Q).

Coenzyme Q/Co Q

(ubiquinone)

Transfer electrons to cytochrome c

reductase.

Cytochrome c

reductase

Transfer electrons to cytochrome c.


Cytochrome c Transfer electrons to cytochrome oxidase.

Cytochrome c

oxidase

Transfer electrons to O2, forming H2O.


What would happen when NADH reaches electron transport

chain?

1. NADH is oxidized to form NAD+. Electrons are transferred

to NADH dehydrogenase.

2. As high energy electron is transferred some of the energy is

harnessed to pump proton out from the matrix of

mitochondria into the intermembrane space of

mitochondria

3. NADH dehydrogenase passes electrons to ubiquinone.

Ubiquinone molecule that receives electron is reduced,

NADH dehydrogenase molecule which donated electron is

oxidized

4. Ubiquinone (a mobile electron carrier) passes electrons to

Cytochrome c reductase

5. Ubiquinone is oxidized, Cyt. c reductase is reduced.

6. Cytochrome c reductase passes electrons to Cytochrome c.

7. Cyt. c reductase is oxidized, Cyt. c is reduced. As electron

is transferred, proton is pumped into the intermembrane

space of mitochondria


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MAIN IDEAS


8. Cytochrome c (a mobile electron carrier) passes electrons

to Cytochrome c oxidase.

9. Cytochrome c oxidase is oxidised, Cyt c oxidase is

reduced.

10. Cytochrome c oxidase passes electrons to oxygen (last

electron acceptor). Water is produced.

11. As electron is transferred, proton is pumped into the

intermembrane space of mitochondria

What would happen when FADH2 reaches electron transport

chain?

1. FADH2 passes electrons to succinate dehydrogenase

2. Succinate dehydrogenase passes electrons to ubiquinone

3. Ubiquinone passes electrons to cytochrome c reductase

4. Cytochrome c reductase passes electrons to cytochrome c

5. Cytochrome c passes electrons to cytochrome c oxidase

6. Cytochrome c oxidase passes electrons to oxygen atom

(final electron acceptor)

7. Oxygen ion reacts with hydrogen ions in mitochondrial

matrix, forming water

Chemiosmosis

Definition: The production of ATP via proton movement, through

ATP synthase across a membrane, driven by proton gradient.

How does the mitochondrion couple this electron transport and

energy release to ATP synthesis?

- The chain uses the energy flow of electron to pump H+ from

the mitochondrial matrix to the intermembrane space of

mitochondrion.

- Results higher concentration of H+ in the intermembrane space

- Proton gradient across the inner membrane creates proton-

motive force

- H+ in the intermembrane space flow back to mitochondrial

matrix.

- Protons enter the mitochondrial matrix via ATP synthase,

which powers the production of ATP.

- ATP synthase uses the energy of the proton gradient to

catalyze the synthesis of ATP.


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MAIN IDEAS


What is ATP Synthase?

A membrane-bound enzyme in chloroplasts and mitochondria that

uses the energy of protons flowing through it to synthesize ATP.

Utilization of

NADH &

FADH2

1 NADH transfer a pair of electrons generates 3 ATP.

1 FADH2 , transfer a pair of electrons generates 2 ATP.

Complete

oxidation of one

molecule of

glucose

During cellular respiration, most energy flows in this sequence:

Process ATP produce

Glycolysis: Glucose into pyruvate 2 ATP (Substrate Level

Phosphorylation)

Glycolysis: 2 (NADH + H+)

(Glycerol shuttle = 4 ATP) eg:

muscle, brain

(Malate shuttle = 6 ATP) In active

cells eg liver, kidney and heart

4 ATP

or

6 ATP

Link Reaction: Pyruvate (2) to

acetyl CoA yield 2 (NADH + H+)

6 ATP

Krebs Cycle:

2 GTP = 2 ATP

6 (NADH + H+) = 18 ATP

2 (FADH2) = 4 ATP

24 ATP

TOTAL 36 or 38 ATP


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SUBTOPIC : 5.2 Fermentation and its application

LEARNING OUTCOMES: (a) Explain lactate and alcohol fermentation

(b) State the importance of fermentation in industry

MAIN IDEAS


Fermentation

A catabolic process that makes a limited amount of ATP from

glucose (or other organic molecules) without an electron

transport chain and that produces a characteristic end product,

such as ethyl alcohol or lactic acid.

(Campbell, 11th edition)


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MAIN IDEAS


Types of

fermentation

Lactate Fermentation

• This type of fermentation is used routinely in mammalian

red blood cells and in skeletal muscle that has an

insufficient oxygen supply to allow aerobic respiration to

continue (that is, in muscles used to the point of fatigue).

• Pyruvate is reduced by NADH.

• Forming lactate as an end product.

• No release of CO2.

• Some fungi and bacteria - to make cheese and yogurt.

• Human muscle - to generate ATP when O2 is scarce. In

muscles, lactic acid accumulation must be removed by the

blood circulation and the lactate brought to the liver for

further metabolism. Such lactic acid accumulation was once

believed to cause muscle stiffness, fatigue, and soreness,


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MAIN IDEAS


Types of

fermentation

Alcohol Fermentation

• Pyruvate is converted into acetaldehyde.

o The first reaction is catalyzed by pyruvate

decarboxylase. A carboxyl group is removed from

pyruvic acid, releasing carbon dioxide as a gas.

• Acetaldehyde is reduced by NADH to become ethanol.

o The second reaction is catalyzed by alcohol

dehydrogenase to oxidize NADH to NAD+ and

reduce acetaldehyde to ethanol.

Compare the lactate fermentation and alcohol

fermentation.

Similarities

- Both are in anaerobic condition/ absence of oxygen.

- Both undergo glycolysis.

- Both used 2 pyruvates formed from glycolysis.

- Both used NADH (+ H+) as reducing agent.

- Both produce Net 2 ATP.


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MAIN IDEAS


Differences

Lactate Fermentation Alcohol Fermentation

Produce lactate/ lactic acid Produce ethanol

No intermediate substrate Produce intermediate

substrate which

acetaldehyde

No CO2 released/ no

decarboxylation occur

CO2 released/

decarboxylation occur

Occur in mammal muscle

cell// animal cell

Occur in yeast// plant cell

Importance of

fermentation in

industry

• Bakery for production of bread to improve the taste, pH and texture of the product

• In brewing, for production of alcohol/ wine / vinegar. Turn starch in malt/rice/ corn

into maltose, dextrin and water

• In dairy industry, for production of cheese & yogurt

• In local / tradisional products,eg: tempe/ budu/ tapai /thosai

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CHAPTER 5: CELLULAR RESPIRATION AND FERMENTATION