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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
Lightenergy
ECOSYSTEM
Photosynthesis in chloroplasts
CO2 + H2O Cellular
respirationin mitochondria
Organicmolecule
s
+ O2
ATP powers most cellular work
Heatenergy
ATP
The Flow of Energy from Sunlight to ATP
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. 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)
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.
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)
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Na will easily lose its outer electron to Cl . Why?In this reaction, which atom is oxidized?Which is reduced?
becomes oxidized
becomes reduced
In cellular respiration, glucose is broken down and loses its electrons in the process. The glucose becomes oxidized and the Oxygen is reduced.
Redox Reactions of Cellular Respiration
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.
Fre
e en
erg
y, G
Fre
e en
erg
y, G
(a) Uncontrolled reaction
H2O
H2 + 1/2 O2
Explosiverelease of
heat and lightenergy
(b) Cellular respiration
Controlledrelease ofenergy for
synthesis ofATP
2 H+ + 2 e–
2 H + 1/2 O2
(from food via NADH)
ATP
ATP
ATP
1/2 O22 H+
2 e–E
lectron
transp
ort
chain
H2O
Energy is released a little at a time, rather than one big explosive reaction:
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
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electronscarried
via NADH
An Overview of Cellular Respiration–Part 1
Mitochondrion
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electronscarried
via NADH
Substrate-levelphosphorylation
ATP
Electrons carriedvia NADH and
FADH2
Citricacidcycle
An Overview of Cellular Respiration—Part 2
Mitochondrion
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electronscarried
via NADH
Substrate-levelphosphorylation
ATP
Electrons carriedvia NADH and
FADH2
Oxidativephosphorylation
ATP
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
An Overview of Cellular Respiration—Part 3
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!
“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.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_glycolysis_works.html
Energy investment phase
Glucose
2 ADP + 2 P 2 ATP used
formed4 ATP
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+
2 Pyruvate + 2 H2O
2 Pyruvate + 2 H2OGlucoseNet
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+
Glycolysis
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.
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.
CYTOSOL MITOCHONDRION
NAD+ NADH + H+
2
1 3
Pyruvate
Transport protein
CO2Coenzyme A
Acetyl CoA
Converting Pyruvate to 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 (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
The Citric Acid Cycle
Oxaloacetate + Acetyl CoA Citric Acid
Acetyl CoA
CoA—SH
Citrate
H2O
IsocitrateNAD+
NADH
+ H+
CO2
-Keto-glutarate
CoA—SH
CO2NAD+
NADH
+ H+SuccinylCoA
CoA—SH
P i
GTP GDP
ADP
ATP
Succinate
FAD
FADH2
Fumarate
CitricacidcycleH2O
Malate
Oxaloacetate
NADH
+H+
NAD+
1
2
3
4
5
6
7
8
The Citric Acid Cycle:
http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__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.
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
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Oxygen is the final electron acceptor.
NADH
NAD+2FADH2
2 FADMultiproteincomplexesFAD
Fe•S
FMN
Fe•S
Q
Fe•S
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
IV
Fre
e en
erg
y (G
) r e
lat i
ve t
o O
2 (
kcal
/mo
l)
50
40
30
20
10 2
(from NADHor FADH2)
0 2 H+ + 1/2 O2
H2O
e–
e–
e–
The Electron Transport Chain
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 free-energy drop from food to O2 into smaller steps that release energy in manageable amounts
http://www.youtube.com/watch?v=xbJ0nbzt5Kw
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
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
Rotor
H+
Stator
Internalrod
Cata-lyticknob
ADP+P ATP
i
MITOCHONDRIAL MATRIX
ATPSynthase
Protein complexof electroncarriers
H+
H+H+
Cyt c
Q
V
FADH2 FAD
NAD+NADH
(carrying electronsfrom food)
Electron transport chain
2 H+ + 1/2O2H2O
ADP + Pi
Chemiosmosis
Oxidative phosphorylation
H+
H+
ATP synthase
ATP
21
Chemiosmosis couples the electron transport chain to ATP synthesis
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
Maximum per glucose: About36 or 38 ATP
+ 2 ATP+ 2 ATP + about 32 or 34 ATP
Oxidativephosphorylation:electron transport
andchemiosmosis
Citricacidcycle
2AcetylCoA
Glycolysis
Glucose2
Pyruvate
2 NADH 2 NADH 6 NADH 2 FADH2
2 FADH2
2 NADHCYTOSOL Electron shuttles
span membrane
or
MITOCHONDRION
ATP Yield per molecule of glucose at each stage of cellular respiration: