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 If you need to take the quiz, see me.
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SCIENCE QUESTION OF THE DAY

Name the chief currency of the cells energy and
where in the cell it is made.
ANSWER
Chief energy currency of the cell is ATP.
 It is made in the mitochondria of the cell.

REVIEW TIME
Food
 Energy
 ATP
 Mitochondria
 Membrane bound organelles
 Permeability
 Investing and harvesting ATP
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
6.6 An Overview of
Cellular Respiration
Cellular respiration:
Harvesting of energy from breakdown of organic molecules
produced by plants
The overall process may be summarized as
C6H12O6
glucose
+
6 O2
6 CO2
oxygen
carbon
dioxide
+
6 H2O
water
+
energy
(heat or ATP)
Cellular respiration is carried out in two stages:
Occurs in the cytoplasm
1. Glycolysis
2. Oxidation
Occurs in the mitochondria
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Fig. 6.16 An overview of
aerobic respiration
Oxygen is the terminal
electron acceptor in
aerobic respiration
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6.7 Using Coupled Reactions
to Make ATP
Glycolysis is the first stage in cellular respiration
Takes place in the cytoplasm
Occurs in the presence or absence of oxygen
Involves ten enzyme-catalyzed reactions
These convert the 6-carbon glucose into two
3-carbon molecules of pyruvate
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Pyruvate
is oxidized
Pyruvate
is reduced
Occurs in animal
muscle cells
Occurs in
yeast cells
Fig. 6.19
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Fig. 6.17 How glycolysis works
Priming reactions
1
6-carbon glucose
(Starting material)
Cleavage reactions
2
Energy-harvesting reactions
3
2 ATP
P
P
6-carbon sugar diphosphate
P
P
6-carbon sugar diphosphate
P
P
P
P
3-carbon sugar 3-carbon sugar 3-carbon sugar 3-carbon sugar
phosphate
phosphate
phosphate
phosphate
NADH
NADH
2 ATP
2 ATP
3-carbon 3-carbon
pyruvate pyruvate
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Fig. 6.18 Glycolysis
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Fig. 6.18 Glycolysis
This coupled reaction is
called substrate-level
phosphorylation
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6.8 Harvesting Electrons
from Chemical Bonds
Fig. 6.20
The oxidative stage of
aerobic respiration
occurs in the
mitochondria
It begins with the
conversion of pyruvate
into acetyl coA
Depending
on needs
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6.8 Harvesting Electrons
from Chemical Bonds
Substrate is oxidized
NAD+ is reduced
Fig. 6.21 How NAD+ works
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The Krebs Cycle
Takes place in the mitochondria
It consists of nine enzyme-catalyzed reactions that
can be divided into three stages
Stage 1
Acetyl coA binds a four-carbon molecule
producing a six-carbon molecule
Stage 2
Two carbons are removed as CO2
Stage 3
The four-carbon starting material is regenerated
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Fig. 6.22 How the Krebs cycle works
1
3
2
CoA–
(Acetyl-CoA)
4-carbon molecule
(Starting material)
6-carbon
molecule
6-carbon molecule
NADH
CO2
4-carbon
molecule
ATP
5-carbon
molecule
4-carbon molecule
(Starting material)
NADH
FADH2
4-carbon molecule
NADH
CO2
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Fig. 6.23 The Krebs cycle
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Copyright ©The McGraw-Hill Companies, Inc. Permission required for reproduction or display
Fate of Glucose
Glucose is entirely consumed in the process of
cellular respiration
It is converted to six molecules of CO2
Its energy is preserved in
Four ATP molecules
Ten NADH electron carriers
Two FADH2 electron carriers
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6.9 Using the Electrons to Make ATP
The NADH and FADH2 carry their high-energy
electrons to the inner mitochondrial membrane
There they transfer them to a series of membraneassociated carriers – the electron transport chain
Three of these carriers are protein complexes
that pump protons out of the matrix
The electrons are finally donated to oxygen to form
water
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Fig. 6.24 The electron transport chain
Intermembrane space
H+
NADH activates
all three pumps
H+
H+
e–
e–
FADH2
NADH +H+
Inner
mitochondrial
membrane
NAD+
Protein
complex I
FADH2 activates
only two pumps
2H+ +
½ O2
Protein
complex II
Mitochondrial matrix
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Protein
complex III
H2O
The proton pumps lead to an increase in proton
concentration in the intermembrane space
The proton
gradient induces
the protons to
reenter the matrix
through ATP
synthase channels
The proton reentry
drives the
synthesis of ATP
by chemiosmosis
Fig. 6.25
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Fig. 6.26 An overview of the electron transport chain and chemiosmosis
Intermembrane space
Pyruvate from
cytoplasm
H+
H+
e–
NADH
H+
1. Electrons are harvested
and carried to the transport
system.
Acetyl-CoA
2. Electrons provide
energy to pump
protons across the
membrane.
e–
NADH
H2O
e–
Krebs
cycle
FADH2
3. Oxygen joins with
protons to form water.
1
2
+
O2
O2
2H+
CO2
32
2
ATP
H+
ATP
Mitochondrial matrix
4. Protons diffuse back
in, driving the synthesis
of ATP.
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ATP
synthase
Other Sources of Energy
Food sources, other than sugars, can be used in
cellular respiration
These complex molecules are first digested into
simpler subunits
These subunits are modified into intermediates
These intermediates enter cellular respiration
at different steps
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Fig. 6.27
How cells
obtain
energy
from foods
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Anaerobic Respiration
The use of inorganic terminal electron acceptors
other than oxygen
Organism
TEA
Reduced
Product
Methanogens
Archaea
CO2
CH4
Sulfur bacteria
Methane
SO4
H2S
Sulfate
Hydrogen
sulfide
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Fermentation
The use of organic terminal electron acceptors
The electrons carried by NADH are donated to a
derivative of pyruvate
This allows the regeneration of NAD+ that keeps
glycolysis running
Two types of fermentation are common among
eukaryotes
Lactic fermentation
Ethanolic fermentation
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