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Cellular Respiration
The role of ATP
~
~
~ high energy bonds
~
How is ATP formed?
Energy released from respiration converts ADP and an
inorganic phosphate into ATP.
ADP + Pi  ATP
The energy is used to build up an additional high energy
bond in the ATP molecule.
How is the energy in ATP
molecule made available for
metabolic process?
The ATP molecule is hydrolyzed by enzyme ATPase to ADP
and inorganic phosphate molecules. The energy of the high
energy bond is released coupling with endogonic biochemical
reaction.
ATP  ADP + Pi + energy
Energy is used in an endogonic biochemical reaction.
Use of Energy
The three main stages of aerobic respiration
Glycolysis
It takes place in cytoplasm.
The first step is the activation of
glucose by phosphorylating it into a
hexose phosphate.
Hexose phosphate splits up into two
molecules of triose phosphate.
Triose phosphate is dehydrogenated
and further metabolized to form
pyruvate. ATP molecules are formed.
The products formed in glycolysis are
reduced NAD, pyruvate and ATP
molecules.
Krebs cycle
There is a bridge between glycolysis
and Krebs cycle. It is decarboxylation
and dehydrogenation of the pyruvate
to Acetyl coenzyme A.
The Acetyl Coenzyme A then enters
the Krebs cycle as shown. In the
Krebs cycle, there are:
1. Decarboxylation
2. Dehydrogenation
3. Formation of ATP.
All the above processes take place in the matrix of mitochondrion.
Oxidative phosphorylation
All dehydrogenation is coupled with transference of hydrogen or
electron through a series of enzymes, coenzymes and prosthetic
groups located at the mitochondrial cristae. The final acceptor for
the hydrogen is oxygen molecules resulting in formation of water.
The above transference of hydrogen and electron is a series of redox
reaction in a stepwise and controlled manner. Energy is released step
by step. The energy release is coupled with phosphorylation of ADP
into ATP.
Therefore the whole process is called Oxidative phosphorylation.
Alternative respiratory substrates for aerobic respiration
Alternative respiratory substrates for aerobic respiration
Aerobic Respiration using lipid as the substrate
Lipid is hydrolysed into fatty acid and glycerol.
Glycerol is converted to triose phosphate which
enters glycolysis and then Krebs cycle.
Fatty acid is converted into Acetyl Coenzyme A
which enters the Krebs cycle.
Oxidative phosphorylation follows the above two
pathways.
Alternative respiratory substrates for aerobic respiration
Aerobic respiration using protein as the substrate
Protein is hydrolyzed into amino acids.
The various kinds of amino acids are converted into three special
kinds of amino acids called alanine, aspartic acid and Glutamic acid
by transamination.
These three amino acids are converted into three alpha keto acids:
Alanine  pyruvate
Aspartic acid  Oxaloacetic acid
Glutamic acid  alpha keto-glutaric acid
These three compounds are the intermediates of glycolysis and
Krebs cycle.
Oxidative phosphorylation follows the above processes.
Differences between photophosphorylation
and oxidative phosphorylation
Photophosphorylation
Takes place in the grana and
intergrana of chloroplast
Sunlight is the energy source.
Oxidative phosphorylation
It takes place at the
mitochondrial cristae.
Energy source is from food.
Enzymes are required for
It is photochemical reaction
and does not require enzymes. ALL steps.
NADP is the carrier of H.
NAD is the carrier for H.
Anaerobic Respiration
What are the two main products of glycolysis?
NADH2 and pyruvate
What is the fate of these products under aerobic condition?
Both enter the mitochondrion to undergo Krebs cycle and
oxidative phosphorylation.
What is the fate of the products of glycolysis under anaerobic
condition?
See the next page.
Anaerobic Respiration
Anaerobic Respiration
In animal cell, the pyruvate is reduced by the NADH2 to lactic
acid.
It is called lactic acid fermentation.
Pyruvate + NADH2  Lactic acid + NAD
The above pathway takes place in cytoplasmic matrix.
Anaerobic Respiration
In plant cell, the pyruvate is reduced by the NADH2 to ethanol
and carbon dioxide.
It is called alcoholic fermentation
Pyruvate + NADH2  ethanol + carbon dioxide + NAD
The above pathway takes place in cytoplasmic matrix.
Application of alcoholic fermentation:
Manufacturing of wine, beer, bread and cake
Anaerobic Respiration
No Krebs cycle and oxidative phosphorylation
Only glycolysis is involved.
Anaerobic Respiration
Obligate anaerobes: They can respire only in the absence
of oxygen. Oxygen is a poison to these organisms. E.g.
denitrifying bacteria.
Facultative anaerobes: They can respire aerobically in the
presence of oxygen. They can respire anaerobically in the
absence of oxygen. E.g. yeast
Comparison between aerobic and anaerobic respiration
Aerobic respiration Anaerobic
respiration
Yield of ATP
Higher
Lower
Energy in the
products
Products have
lower energy
Products have
higher energy
What process
involve?
Glycolysis, Krebs
cycle, oxidative
phosphorylation
Where does it take Cytoplasmic
place?
matrix and
Glycolysis only
Cytoplasmic
matrix only
Comparison between aerobic and anaerobic respiration
Do you have any other points?
Oxygen Debt
Oxygen Debt
Oxygen consumption
rate
Time
A
B
C
D
A: Exercise starts
B: Anaerobic respiration starts and oxygen debt is built up.
C: Exercise stops. The person pants for paying off the oxygen debt.
D: Oxygen debt is paid off.
Mitochondrion
Mitochondrion
The outermembrane of the mitochondrial envelop is to establish an
isolated environment for the mitochondrion. This membrane also
adjusts the metabolites entering and leaving the mitochondrion.
The inner membrane is folded up a lot to increase the surface area
for attachment of ETC. These infolds are called cristae.
Attaching to the cristae are many stalked particles which contain the
various enzymes, coenzymes and prosthetic groups of ETC.
Glycolysis takes place in the cytoplasmic matrix outside the
mitochondrion.
Pyruvate enters the mitochondrial matrix to undergo
decarboxylation and Krebs cycle.
Oxidative phosphorylation takes place along the ETC of the stalked
particles of the cristae.
Compare and contrast chloroplast and Mitochondrion
Similarities
Both have envelop of double membranes.
Both involves formation of ATP.
Both contains DNA and are self-replicated.
Compare and contrast chloroplast and Mitochondrion
Differences
Mitochondrion is found in all living cells; chloroplast can be found in
photosynthetic cell of plant only.
Mitochondrion is for aerobic respiration; chloroplast is for
photosynthesis.
The inner membrane of mitochondrion has a lot of infolds; the inner
membrane of chloroplast is smooth.
Compare the differences between photosynthesis
and aerobic respiration
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