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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
/KEY POINT EXPLANATION NOTES
• 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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
▪ 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.
Pump proton into the intermembrane space
Cytochrome c Transfer electrons to cytochrome oxidase.
Cytochrome c
oxidase
Transfer electrons to O2, forming H2O.
Pump proton into the intermembrane space
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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
/KEY POINT EXPLANATION NOTES
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