Download AP Biology Ch. 9 Cellular Respiration

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

Organisms must take in
energy from outside
sources.
Energy is incorporated
into organic molecules
such as glucose in the
process of
photosynthesis.
Glucose is then broken
down in cellular
respiration. The energy
is stored in ATP.
Fig. 9-2
The
Flow of
Energy
from
Sunlight
to ATP
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O
Cellular respiration
in mitochondria
Organic
+
molecules
O2
ATP
ATP powers most cellular work
Heat
energy

Energy in food is stored as carbohydrates
(such as glucose), proteins & fats. Before
that energy can be used by cells, it must be
released and transferred to ATP.

Aerobic Cellular Respiration: the process that
releases energy by breaking down food
(glucose) molecules in the presence of oxygen.

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Formula: C6H12O6 + 6O2 → 6CO2 + 6H2O +~ 36 ATP
Fermentation: the partial breakdown of glucose
without oxygen. It only releases a small
amount of ATP.
Glycolysis: the first step of breaking down
glucose—it splits glucose (6C) into 2 pyruvic
acid molecules (3C each)
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
Adenosine triphosphate (ATP) “stores” energy
in the bonds between its’ 3 phosphates.
ATP has the sugar ribose, the nitrogen base
adenine, and 3 phosphoric acids.


The transfer of electrons during chemical
reactions releases energy stored in organic
compounds such as glucose.
Oxidation-reduction reactions are those that
involve the transfer of an electron from one
substance to another.
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•
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Chemical reactions that transfer electrons between
reactants are called oxidation-reduction reactions,
or redox reactions
In oxidation, one substance loses electrons, or is
oxidized
In reduction, a substance gains electrons, or is
reduced (the amount of positive charge is reduced)
Na will easily lose its outer
electron to Cl . Why?
In this reaction, which atom is
oxidized?
Which is reduced?
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Redox Reactions of Cellular Respiration
In cellular respiration, glucose is broken down and
loses its electrons in the process.
The glucose becomes oxidized and the Oxygen is
reduced.
becomes oxidized
becomes reduced
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
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In cellular respiration, glucose is broken down
in a series of steps.
As it is broken down, electrons from glucose
are transferred to NAD+, a coenzyme
When it receives the electrons, it is converted to
NADH.
NADH
represents
stored energy
that can be
used to make
ATP


NADH passes the electrons to the electron
transport chain, a series of proteins embedded
in the inner membrane of the mitochondria.
The electrons (and the energy they carry) are
transferred from one protein to the next in a
series of steps.
Energy is released a little at a time, rather than one big explosive reaction:
H2 + 1/2 O2
2H
(from food via NADH)
Controlled
release of
+
–
2H + 2e
energy for
synthesis of
ATP
1/
2 O2
Explosive
release of
heat and light
energy
1/
(a) Uncontrolled reaction
(b) Cellular respiration
2 O2
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Cellular respiration has three stages:



Glycolysis (breaks down glucose into two molecules of
pyruvate)
The Citric Acid cycle/Kreb’s Cycle (completes the
breakdown of glucose)
Electron Transport Chain and Oxidative
phosphorylation (accounts for most of the ATP
synthesis)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
An Overview of Cellular Respiration–Part 1
Electrons
carried
via NADH
Glycolysis
Pyruvate
Glucose
Cytosol
ATP
Substrate-level
phosphorylation
An Overview of Cellular Respiration—Part 2
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Mitochondrion
Cytosol
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
An Overview of Cellular Respiration—Part 3
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolysis
Pyruvate
Glucose
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
Mitochondrion
Cytosol
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation


Substrate-level
phosphorylation:
Phosphate is added to
ADP to make ATP by
using an enzyme:


Oxidative
phosphorylation:
Phosphate is added to
ADP to make ATP by
ATP Synthase—a
protein embedded in
the mitochondria
membrane (requires
O2)
WAY MORE
EFFICIENT!!
PRODUCES LOTS
MORE ATP!
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“Glyco”=sugar; “lysis”=to split
In this first series of reactions, glucose (C6) is
split into two molecules of pyruvic acid (C3).
This occurs in the cytoplasm of cells and does
not require oxygen.
This releases only 2 ATP molecules, not enough
for most living organisms.
http://highered.mcgrawhill.com/sites/0072507470/student_view0/cha
pter25/animation__how_glycolysis_works.htm
l
Energy investment phase
Glycolysis
Glucose
2 ADP + 2 P
2 ATP
used
4 ATP
formed
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Net
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H+
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
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
The Citric Acid Cycle (also called the Kreb’s
Cycle) completes the breakdown of pyruvate
and the release of energy from glucose.
It occurs in the matrix of the mitochondria.
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
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In the presence of oxygen, pyruvate enters the
mitochondria.
Before the pyruvate can enter the Citric Acid
Cycle, however, it must be converted to Acetyl
Co-A.
Some energy is released and NADH is formed.
Converting Pyruvate to Acetyl CoA:
MITOCHONDRION
CYTOSOL
NAD+
NADH + H+
2
1
Pyruvate
Transport protein
3
CO2
Coenzyme A
Acetyl CoA



The Acetyl Co-A enters the Citric Acid Cycle in
the matrix of the mitochondria.
The Citric Acid cycle breaks down the Acetyl
Co-A in a series of steps, releasing CO2
It produces 1 ATP, 3 NADH, and 1 FADH2 per
turn.
The Citric Acid Cycle
•
•
•
The Citric Acid cycle (also called the Krebs Cycle)
has eight steps, each catalyzed by a specific
enzyme
The acetyl group of acetyl CoA joins the cycle by
combining with oxaloacetate, forming citrate
(Citric Acid).
The next seven steps decompose the citrate
(Citric Acid) back to oxaloacetate, making the
process a cycle
Oxaloacetate + Acetyl CoA
Citric Acid
The
Citric
Acid
Cycle:
Acetyl CoA
CoA—SH
NADH
+H+
H2O
1
NAD+
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
Citric
acid
cycle
7
H2O
NADH
+ H+
3
CO2
Fumarate
CoA—SH
6
-Ketoglutarate
4
CoA—SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2

http://highered.mcgrawhill.com/sites/0072507470/student_view0/cha
pter25/animation__how_the_krebs_cycle_wor
ks__quiz_1_.html
•
•
Each Citric Acid Cycle only produces 1 ATP
molecule. The rest of the energy from pyruvate
is in the NADH and FADH2.
The NADH and FADH2 produced by the Citric
Acid cycle relay electrons extracted from food
to the electron transport chain.
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The electron transport chain is in the cristae of
the mitochondrion
Most of the chain’s components are proteins,
which exist in multiprotein complexes
The carriers alternate reduced and oxidized
states as they accept and donate electrons
Electrons drop in free energy as they go down
the chain and are finally passed to O2, forming
H2O
Oxygen is the final electron acceptor.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The
Electron
Transport
Chain
NADH
50
2 e–
NAD+
FADH2
2 e–
40

FMN
FAD
Multiprotein
complexes
FAD
Fe•S 
Fe•S
Q

Cyt b
30
Fe•S
Cyt c1
I
V
Cyt c
Cyt a
Cyt a3
20
10
2 e–
(from NADH
or FADH2)
0
2 H+ + 1/2 O2
H2O
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Electrons are transferred from NADH or
FADH2 to the electron transport chain
Electrons are passed through a number of
proteins to O2
The chain’s function is to break the large freeenergy drop from food to O2 into smaller steps
that release energy in manageable amounts

http://www.youtube.com/watch?v=xbJ0nbzt
5Kw
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Electron transfer in the electron transport chain
causes proteins to pump H+ from the
mitochondrial matrix to the intermembrane
space
H+ then moves back across the membrane,
passing through channels in ATP synthase
Animation:
http://sp.uconn.edu/~terry/images/anim/ETS.
html
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
ATP synthase uses the exergonic flow of H+ to
drive phosphorylation of ATP
This is an example of chemiosmosis, the use of
energy in a H+ gradient to drive cellular work
INTERMEMBRANE SPACE
ATP
Synthase
H+
Stator
Rotor
Internal
rod
Catalytic
knob
ADP
+
P
i
ATP
MITOCHONDRIAL MATRIX
Chemiosmosis couples the electron transport chain to ATP
synthesis
H+
H+
H+
H+
Protein complex
of electron
carriers
Cyt c
V
Q


ATP
synthase

FADH2
NADH
2 H+ + 1/2O2
H2O
FAD
NAD+
ADP + P i
(carrying electrons
from food)
ATP
H+
1 Electron transport chain
Oxidative phosphorylation
2 Chemiosmosis


During cellular respiration, most energy flows
in this sequence:
glucose  NADH  electron transport chain
 proton-motive force  ATP
About 40% of the energy in a glucose molecule
is transferred to ATP during cellular
respiration, making about 38 ATP
+ 6 O2
6CO2 + 6H2O + 38 ATP
ATP Yield per molecule of glucose at each stage of cellular
respiration:
Electron shuttles
span membrane
CYTOSOL
2 NADH
Glycolysis
Glucose
2
Pyruvate
MITOCHONDRION
2 NADH
or
2 FADH2
6 NADH
2 NADH
2
Acetyl
CoA
+ 2 ATP
Citric
acid
cycle
+ 2 ATP
Maximum per glucose:
About
36 or 38 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP