CHAPTER 5: CELLULAR RESPIRATION

CHAPTER 5: CELLULAR RESPIRATION SES SEMESTER II: DB024
CHAPTER 5: CELLULAR RESPIRATION

5.1 IMPORTANCE OF ENERGY

Needs for energy in living organisms
▪ Living things require a continual supply of energy in order to carry out life processes such as movement,

active transport, cell division and others.
▪ Cellular respiration is a catabolic process that converts chemical energy stored in organic molecules

(glucose) into energy (ATP)
✓ ATP is a form of chemical energy that is readily to be used by the cell
✓ The sources of energy in cellular respiration are glucose (major), fat & protein.

ATP as the main source of chemical energy

▪ ATP is common energy currency of the cell.
▪ ATP is a nucleotide in which adenosine (ribose sugar + adenine base) molecule bonded to three phosphates

molecules. ATP release free energy when bond within phosphate group is hydrolyzed (phosphoanhydride

bond).

▪ ATP has unstable phosphate bonds. The energy is trapped in these two high energy bonds.

✓ When energy is needed, ATP is broken down/ hydrolyzed into ADP and Pi.

✓ Equation: ATP ADP + Pi + energy

✓ These yields about 7.3 kcal mol-1 of energy.

✓ Energy will be transferred to cell which requires energy to carry out cellular activities

▪ ATP can be re-synthesized from an ADP by re-attaching a phosphate group to ADP, through

phosphorylation process.

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CHAPTER 5: CELLULAR RESPIRATION SES SEMESTER II: DB024

TYPES OF RESPIRATION: AEROBIC, ANAEROBIC AND FERMENTATION

CELLULAR RESPIRATION

Glycolysis
(Oxidation of glucose in cytoplasm)

Aerobic (O2 present) Anaerobic (O2 absent) Fermentation
- (O2 absent and no
Link Reaction
Link Reaction final electron
Krebs Cycle acceptor)
Krebs Cycle
Oxidative Ethanol/ Alcoholic
Phosphorylation; Oxidative fermentation
Electron Transport Phosphorylation; (Yeast)
Electron Transport
Chain Chain & Chemiosmosis Lactic Acid
Use O2 as final Use other than O2 as fermentation
electron acceptor final electron acceptor
(CO2, NO3-, SO2-4) (Muscle)
Chemiosmosis
Chemiosmosis

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CHAPTER 5: CELLULAR RESPIRATION SES SEMESTER II: DB024
5.2 AEROBIC RESPIRATION

I. AEROBIC RESPIRATION
▪ Definition: The complete oxidation of glucose to produce CO2, H2O and ATP in the presence of

oxygen
▪ Catabolic pathway for organic molecules using oxygen as final electron acceptor in ETC and produce

ATP.
▪ Equation: C6H12O6 (glucose) + 6O2 ➔ 6CO2 + 6H2O + Energy (38 ATP+ heat)
▪ In eukaryotic cells, this process occurs in the cytoplasm and mitochondria
▪ STAGES OF AEROBIC RESPIRATION:

Stages Location
Glycolysis Cytosol / cytoplasm
Link reaction Mitochondrial matrix
Krebs cycle Mitochondrial matrix
Electron transport chain and Chemiosmosis Inner mitochondrial membrane/ cristae

TYPE OF ATP PRODUCTION
Phosphorylation

A process of adding phosphate to an organic molecule. i.e.: ADP is phosphorylated to ATP

i. Substrate level phosphorylation ii. Oxidative phosphorylation
▪ The formation of ATP when an enzyme directly ▪ The production of ATP via chemiosmosis using

transferring a phosphate group from substrate energy derived from the redox reactions during

to ADP. electron transport chain (involving transfer of
▪ Smaller amount of ATP produced, which is 4
electron)
ATPs via glycolysis & the Krebs cycle (2 ATPs). ▪ Large amount of ATP (34 ATP) are produced per
▪ Does NOT involve ATP synthase
▪ Occur in glycolysis and Krebs cycle molecule of glucose.
▪ Involve ATP synthase
▪ Occur during electron transport chain and

chemiosmosis

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CHAPTER 5: CELLULAR RESPIRATION SES SEMESTER II: DB024
PROCESSES INVOLVED IN CELLULAR RESPIRATION

Redox Reaction (involve oxidation and reduction) Other process involved

Reduction Oxidation

A reaction that: A reaction that: Decarboxylation:
▪ gain electron and ▪ loss electron and hydrogen A reaction in which a molecule of CO2
is removed from a molecule/ substrate
hydrogen atoms atoms E.g.: Pyruvate is converted to acetyl
▪ loss oxygen ▪ gain oxygen CoA
▪ acts as oxidizing agent ▪ acts as reducing agent Dehydrogenation:
▪ E.g. NAD+ reduced to ▪ E.g. Malate is oxidized to form A reaction in which a molecule of
hydrogen is removed from a molecule
form NADH + H+ oxaloacetate

E. g.: Malate is oxidized (transfer 2H + 2e-) to form oxaloacetate
thus NAD+ reduced (accept 2H+ + 2e-) forming NADH +H+

Extra
Information

FIGURE: NAD+ as an electron shuttle

The enzymatic transfer of 2 electrons and 2 protons (H+) from organic molecule to NAD+, thus NAD+
reduce forming NADH + H+.

EQUATION: NAD+ + 2H+ + 2e- NADH + H+

SUMMARY:

NAD+

→ A type of coenzyme consists of two nucleotide join together at their phosphate group.

→ Acts as oxidizing agent
→ NAD+ is reduced to form NADH + H+

NADH
→ Reduced coenzyme
→ Acts as reducing agent
→ NADH is oxidized to form NAD+

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CHAPTER 5: CELLULAR RESPIRATION SES SEMESTER II: DB024

THREE STAGES IN AEROBIC RESPIRATION

I. GLYCOLYSIS

▪ Glycolysis means ‘splitting of sugar’

▪ Splitting of sugar = Splitting of ONE glucose (6C) to TWO pyruvate (3C) molecules

▪ The breakdown of one molecule of glucose in a series of enzyme-catalysed reactions to form two

molecules of pyruvate, accompanied by the production of 2 ATP and 2 NADH

▪ First stage of cellular respiration that occurs in the cytoplasm / cytosol

▪ Glycolysis can occur with or without oxygen

▪ Glycolysis pathway:

✓ Consists of 10 steps

✓ Each step is catalyzed by a specific enzyme

✓ ATP is generated by substrate-level phosphorylation

✓ Can be divided these ten steps into TWO phases:

✓

Energy investment phase (Step 1-5) Energy payoff phase (Step 6-10)

- Phase that use energy (ATP) in - Phase that produce energy (ATP) and

phosphorylation process repaid energy use in step 1-5.

- Convert ONE molecule of glucose (6C) - Convert the TWO molecules of

into TWO molecules of glyceraldehyde-3- Glyceraldehyde-3-phosphate (3C) into

phosphate (G3P) TWO molecules of pyruvate (3C)

✓ Products of glycolysis for ONE molecule of glucose:
→ 2 pyruvate (3C)
→ 2 NADH + 2H+
→ 4 ATP / 2 ATP nett

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CHAPTER 5: CELLULAR RESPIRATION SES SEMESTER II: DB024

I. GLYCOLYSIS PATHWAY :( FROM 1 GLUCOSE TO 2 PYRUVATE)

Hexokinase i. ENERGY INVESTMENT (ATP USE):
Phosphofructokinase 1. Phosphorylation: Phosphorylation of glucose by

ATP, forming glucose-6-phosphate, catalyzed by
hexokinase.

2. Isomerization: Rearrangement of glucose-6-
phosphate to its isomer fructose-6-phosphate

3. Phosphorylation: Phosphorylation of fructose -6-
phosphate by using ATP to form fructose-1,6-
bisphosphate, catalyzed by phosphofructokinase.

4. Cleavage: The unstable 6C molecule is split into
two molecules of 3C, which is:
✓ Dihydroxyacetone phosphate (DHAP)
✓ Glyceraldehyde-3-phosphate (G3P).

5. Isomerization: DHAP converts to its isomer G3P.
Thus, the result is 2 molecules of G3P (3C).

2 NAD + 2 H+ ii. ENERGY PAYOFF (ATP PRODUCED):

HOW TO REMEMBER THE GLYCOLYSIS? 10 words 6. Oxidation and phosphorylation: G3P is oxidized
‘Gross Guys Favor Forest, Gorgeous Boys Prefer Pretty Punk by transfer electron to NAD+. NAD+ is reduced to
NADH + H+. Energy released (from redox
Phone’ reaction) is used to for phosphorylation of oxidized
substrate forming 1, 3-bisphosphoglycerate (3C).
Products of glycolysis for ONE glucose:
▪ 2 pyruvate 7. Substrate-level phosphorylation:
▪ 2 NADH + 2H+ One phosphate group from 1, 3-
▪ Nett are 2 ATP bisphosphoglycerate is transferred to ADP forming
ATP. Thus the remaining substrate is called 3-
phosphoglycerate. (3C)

8. Isomerization: Next, the 3-phosphoglycerate is
rearranged to form 2-phosphoglycerate (3C).

9. Dehydration: Removal of H2O produces
phosphoenolpyruvate (PEP, 3C)

10. Substrate-level phosphorylation: Finally, each
PEP molecule transfers its phosphate group to
ADP forming ATP. PEP is converted to
pyruvate.(3C).

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CHAPTER 5: CELLULAR RESPIRATION SES SEMESTER II: DB024

LINK REACTION (OXIDATION OF PYRUVATE TO ACETYL COENZYME A)

• Step that link glycolysis to the Krebs Cycle
• Steps in which 2 pyruvates from glycolysis (in

cytosol of cell) enters mitochondria as Acetyl-
CoA
• Also known as oxidative decarboxylation
• 3 major steps;
i. Pyruvate is decarboxylated (remove CO2)
ii. The remaining 2 carbon fragments is

oxidised to form acetate, while NAD+ is
reduced to NADH+ + H+
iii.Finally, coenzyme A attached to the
acetate to form Acetyl-CoA.

▪ The products for ONE glucose molecules (2 pyruvate) = 2 Acetyl-CoA, 2 CO2 and 2 NADH + 2H+

II. KREBS CYCLE

What is Krebs Cycle?

▪ Also known as Citric acid cycle or Tricarboxylic acid (TCA) cycle. Occurs in the matrix of mitochondria
▪ To provide electron in the form of NADH and FADH2 that used in the ETC. Eight steps of Krebs

cycle:

1. Condensation: Acetyl-coA removes CoA group,

remaining acetyl (2C) combines with oxaloacetate,

OAA (4C) to form citrate (6C).

2. Isomerization:

Citrate then rearranged to its isomer isocitrate by

removal and addition of one water molecule.

3. Oxidation and decarboxylation:

Isocitrate oxidize, reducing NAD+ to NADH + H+.
The resulting compound loses a molecule of CO2
forming α-ketoglutarate (5C).

4. Decarboxylation and oxidation:
α-ketoglutarate loses a molecule of CO2 forming a

4C molecule. The 4C compound is oxidized,
reducing NAD+ to NADH + H+. The remaining

molecule is attached to coenzyme A to form

succinyl CoA (4C).

5. Substrate level phosphorylation:

Succinyl CoA releases the CoA and displaced by

Pi. The Pi is transferred to GDP, forming GTP.

Then, GTP transfer its phosphate to ADP to form

ATP. Succinyl CoA changed to succinate (4C).

6. Oxidation:

Succinate is oxidized to fumarate (4C) while FAD

is reduced to FADH2

7. Addition of water:

Addition of water rearrange bond in fumarate to

form malate (4C).

HOW TO REMEMBER THE KREBS CYCLE? 8. Oxidation.
8 words Malate is oxidized, reducing NAD+ to NADH + H+,

Orang Cakap I Kuat Sangat Study Fullaa Mak!! regenerating oxaloacetate(4C).

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CHAPTER 5: CELLULAR RESPIRATION SES SEMESTER II: DB024

States the products of Krebs Cycle for each glucose molecule (1 glucose = 2 pyruvate =2 Acetyl CoA)
▪ 6 NADH, 2 FADH2, 2 ATP, 4 CO2

Describe how many ATP is produced via substrate-level phosphorylation in Krebs cycle?
▪ 2 ATP are produced in step 5 (when succinyl CoA converted to succinate)

III. OXIDATIVE PHOSPHORYLATION: ELECTRON TRANSPORT CHAIN (ETC) AND

CHEMIOSMOSIS

What happen during oxidative phosphorylation?
▪ So far, glycolysis and Krebs cycle produce only 4 ATP molecules per glucose through substrate-level

phosphorylation
▪ NADH and FADH2 from glycolysis, link reaction and Krebs cycle are responsible for most of the

energy extracted from the glucose.
▪ So, those NADH and FADH2 act as electron donor/reducing agent/ electron carrier in electron

transport chain (ETC).
▪ The electrons (with high energy) in NADH and FADH2 are transported along the ETC and energy

released by the ETC is used to synthesize ATP by chemiosmosis.
▪ Production of ATP by these processes is called oxidative phosphorylation.

i. Electron Transport Chain (ETC) ii. Chemiosmosis

▪ ETC is a collection of protein molecules that act as electron carriers. ▪ Chemiosmosis is a process

✓ Embedded in the inner membrane (cristae) of the mitochondria. that use energy stored in

✓ It used to transfer electron from NADH and FADH2 to last electron the form of proton (H+)

acceptor, oxygen through series of redox reactions to synthesize gradient across the inner

ATP mitochondrial membrane, to
▪ Components of ETC:
produce ATP from ADP
✓ 4 protein complexes
and Pi.
(i) NADH dehydrogenase (complex I) ▪ Proton (H+) gradient across

(ii) Succinate dehydrogenase (complex II) membrane is also known as

(iii)Cytochrome c reductase (complex III) proton motive force.
▪ Chemiosmosis use protein
(iv)Cytochrome c oxidase (complex IV)
✓ 2 mobile electron carriers complex, ATP synthase,

(i) Ubiquinone/Coenzyme Q (Q) the enzyme that produce

(i) Cytochrome c (Cyt c) ATP from ADP and Pi.

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CHAPTER 5: CELLULAR RESPIRATION SES SEMESTER II: DB024

THE ELECTRON PATHWAY IN ELECTRON TRANSPORT CHAIN;
▪ NADH and FADH2 was produced during glycolysis, link reaction and Krebs cycle.
▪ Electrons carried by NADH are transferred to the NADH dehydrogenase (complex I). Complex I is

reduced while NADH oxidized to NAD+. Complex I passes the electrons to ubiquinone.
▪ While, FADH2 transfer its electrons to succinate dehydrogenase (complex II). Complex II is reduced

while FADH2 oxidized to FAD. Complex II will also passes the electrons to ubiquinone.
▪ Ubiquinone will pass the electron to series of electron carrier complex such as cytochrome c reductase,

cytochrome c and cytochrome c oxidase.
▪ Series of redox reaction occur.
▪ Finally, the electron from complex IV is passed to the last electron acceptor, oxygen to form water.

(2e- + 2H+ + ½ O2 H2O)

▪ As protein complexes accept and donate electrons, energy release is use to pump protons (H+ ion)

from mitochondrial matrix into the intermembrane space by using the energy from series of redox

reaction
▪ For every 1 molecule of NADH, 3 protons are pump out by proton pump at complex I, III and IV.
▪ For every 1 molecule of FADH2, 2 protons are pump out at complex III and IV only. So, it results in

fewer protons being pumped. So, we consider that FADH2 enter the ETC at a lower energy level than

NADH.
▪ This proton pump results in the accumulation of high concentration of protons (H+) in the inter

membrane space also known as proton motive forces.

CHEMIOSMOSIS;
▪ The inner mitochondrial membrane is impermeable to protons (H+).
▪ Accumulation of proton (H+ ion) at intermembrane space, creates proton motive force.
▪ Proton motive force will cause proton (H+ ion) to flow back from intermembrane space into matrix

through ATP synthase.
▪ This exergonic reaction cause ADP to be phosphorylated become ATP.
▪ Each NADH generates 3 ATP (activates three proton pump) but FADH2 generates only 2 ATP

(activates only two proton pump).

PRODUCTION OF ATP, NADH AND FADH2 FOR EACH STAGE OF AEROBIC RESPIRATION.

Complete oxidation of one molecule of glucose in active cells will produce total 38 ATP

(e.g. liver cell, heart cell, kidney cells)

Pathway Substrate-Level Phosphorylation Oxidative Phosphorylation Total
ATP

Glycolysis 2 ATP 2 NADH X 3 = 6 ATP 8

Link Reaction 0 ATP 2 NADH X 3 = 6 ATP 6

Krebs Cycle 2 ATP 6 NADH X 3 = 18 ATP 24
TOTAL 4 ATP 2 FADH X 2 = 4 ATP 38 ATP

2

34 ATP

END OF TOPIC

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