Cell Respiration
Cellular Respiration
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To perform their many
tasks cells require
transfusions of energy
from outside sources
Energy enters ecosystems
as sunlight, the energy
source for plants and
other photosynthetic
organisms
Animals obtain energy by
eating plants or by eating
organisms that eat plants
Cellular Respiration

During cellular respiration organic
compounds are broken down using
oxygen as a reactant
Organic compounds + oxygen
carbon dioxide + water + energy
Cellular Respiration
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Respiration is a stepwise redox (reduction/oxidation) reaction
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Recall: a redox reaction is a transfer of one or more electrons from
one reactant to another
oxidation
Na + Cl2
NaCl
reduction
Cellular Respiration:
oxidation
C6H12O6 + 6O2
6CO2 + 6H2O + energy
reduction
Cellular Respiration
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Energy is not liberated all at once
(explosion!)
http://www.youtube.com/watch?v=pqi50s
jJVc0
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Glucose is broken down gradually
Hydrogen atoms and electrons are stripped from
glucose and are passed to a coenzyme called
nicotinamide adenine dinucleotide (NADH)
Eventually electrons are passed to oxygen in a
series of steps called the electron transport
chain
NAD+ is an oxidizing agent
C
OH + NAD+
Oxidized
form
C
O + NADH
Reduced
form
Four Stages of Respiration
1) Glycolysis (cytoplasm)
2) Pyruvate oxidation (mitochondria)
3) Krebs cycle (citric acid cycle)
4) Oxidative phosphorylation
Glycolysis
- Lysis of sugar
The first stage of respiration
Respiration
Glycolysis splits one molecule of glucose
into two smaller molecules of pyruvate
Glycolysis is the first stage of respiration!
Glycolysis splits one molecule of glucose
into two smaller molecules of pyruvate
Glucose is a hexose
(6-carbon) molecule
Glycolysis is the first stage of respiration!
Glycolysis splits one molecule of glucose
into two smaller molecules of pyruvate
Pyruvate is a triose
(3-carbon) molecule
Glucose is a hexose
(6-carbon) molecule
• Glycolysis takes place in the
cytoplasm of cells.
- it’s the first step for both aerobic and
anaerobic respiration
Glycolysis
2 ADP
2 ADP
Overall Reaction of Glycolysis
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Glucose

2 x pyruvate
There are TWO STAGES of GLYCOLYSIS –
Phosphorylation and Oxidation
Stage One – Phosphorylation:
Investment Phase
http://nhscience.lonestar.edu/biol/glylysis/glylysis
.html
http://programs.northlandcollege.edu/biology/Biology1111/
animations/glycolysis.html
Stage One - Phosphorylation
1-3. Glucose is phosphorylated by
adding 2 phosphates from 2
molecules of ATP to give first
glucose-6-phosphate and finally a
fructose 1,6-bisphosphate.
Stage One - Phosphorylation
4,5. The fructose 1,6-bisphosphate
is split using water (hydrolysis) to
glyceraldehyde-3-phosphate
(G3P)
Glyceraldehyde 3phosphate (G3P)
What’s the point?
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Glucose can now
no longer leave
the cell!!!!
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Molecules produced
are much more
reactive!
Glyceraldehyde 3phosphate
Stage Two – Oxidation (pay-off)
Stage Two - Oxidation
6-10. The G3P is oxidized (loses
electrons), and phosphorylated,
forming two molecules of
pyruvate.
Stage Two - Oxidation
6 cont... Coenzyme NAD+ collects
the hydrogen ions, forming 2
reduced NAD (NADH + H+)
Stage Two - Oxidation
6. Coenzyme NAD+ collects the hydrogen ions,
forming 2 reduced NAD (NADH + H+)
A coenzyme is a helper molecule
that carries chemical groups or ions,
e.g. NAD+ removes H+ and carries it
to other molecules.
The 2 molecules of reduced NADH go
to the electron transport chain
(ETC), part 4 of respiration.
Stage Two - Oxidation
• 4 ATP are produced, but 2 were
used up at the beginning, so
there’s a net gain of 2 ATP.
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Glucose

2 x pyruvate
CHOICES: aerobic or not?
- if aerobic, pyruvate will travel to
mitochondria
Mitochondria
Found in nearly all eukaryotic cells
In animal cells they are oval
Cristae increase surface area and are the
site of electron transport
The matrix is like the cytoplasm of cells
where enzymatic reactions take place
Reaction 2. Pyruvate Oxidation

Second reaction of cellular respiration
Aerobic = Occurs in the presence of
oxygen
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Pyruvate produced in the cytosol is
transported to the mitochondrial matrix
Pyruvate is converted to acetyl-CoA while
NAD+ is reduced to NADH
Link Reaction – 2nd stage of respiration
One carbon atom is
removed from pyruvate in
the form of CO2.
The remaining 2-carbon
molecule combines with
coenzyme A to produce
acetyl coenzyme A
(acetyl CoA).
Another oxidation reaction
happens when NAD+
collects more hydrogen
ions. This forms reduced
NAD (NADH + H+).
No ATP is produced in this
reaction.
The Link reaction happens Twice for
every Glucose Molecule
Link Reaction – 2nd stage of respiration
The Link reaction happens Twice for
every Glucose Molecule
So for every glucose molecule used in
glycolysis, two pyruvate and two acetyl
CoA molecules are made.
So for each glucose molecule:
So for each glucose molecule:
•Two molecules of acetyl CoA go into
Krebs cycle (part 3 of respiration)
So for each glucose molecule:
•Two molecules of acetyl CoA go into
Krebs cycle (part 3 of respiration)
So for each glucose molecule:
•Two molecules of acetyl CoA go into
Krebs cycle (part 3 of respiration)
•Two carbon dioxide molecules are
released as a waste product of respiration
So for each glucose molecule:
•Two molecules of acetyl CoA go into
Krebs cycle (part 3 of respiration)
•Two carbon dioxide molecules are
released as a waste product of respiration
•Two molecules of reduced NAD are
formed and go into the electron
transport chain (part 4 of respiration)
So for each glucose molecule:
•Two molecules of acetyl CoA go into
Krebs cycle (part 3 of respiration)
•Two carbon dioxide molecules are
released as a waste product of respiration
•Two molecules of reduced NAD are
formed and go into the electron
transport chain (part 4 of respiration)