2006-2007
Cellular RespirationStage 4:
Electron Transport Chain
Cellular respiration
2006-2007
What’s thepoint?
The pointis to make
ATP!
ATP
ATP accounting so far… Glycolysis 2 ATP Kreb’s cycle 2 ATP Life takes a lot of energy to run, need to
extract more energy than 4 ATP!
A working muscle recycles over 10 million ATPs per second
There’s got to be a better way!
I need a lotmore ATP!
There is a better way! Electron Transport Chain
series of proteins built into inner mitochondrial membrane along cristae transport proteins & enzymes
transport of electrons down ETC linked to pumping of H+ to create H+ gradient
yields ~36 ATP from 1 glucose! only in presence of O2 (aerobic respiration)
O2That
sounds morelike it!
Mitochondria Double membrane
outer membrane inner membrane
highly folded cristae enzymes & transport
proteins intermembrane space
fluid-filled space between membranes
Oooooh!Form fits function!
Electron Transport Chain
Intermembrane space
Mitochondrial matrix
Q
C
NADH dehydrogenase
cytochromebc complex
cytochrome coxidase complex
Innermitochondrialmembrane
G3PGlycolysis Krebs cycle
8 NADH2 FADH2
Remember the Electron Carriers?
2 NADH
Time tobreak open
the piggybank!
glucose
Electron Transport Chain
intermembranespace
mitochondrialmatrix
innermitochondrialmembrane
NAD+
Q
C
NADH H2O
H+
e–
2H+ + O2
H+H+
e–
FADH2
12
NADH dehydrogenase
cytochromebc complex
cytochrome coxidase complex
FAD
e–
H
H e- + H+
NADH NAD+ + H
H
pe
Building proton gradient!
What powers the proton (H+) pumps?…
H+
H+H+
H+
H+ H+
H+H+H+
ATP
NAD+
Q
C
NADH H2O
H+
e–
2H+ + O2
H+H+
e–FADH2
12
NADH dehydrogenase
cytochrome bc complex
cytochrome coxidase complex
FAD
e–
Stripping H from Electron Carriers Electron carriers pass electrons & H+ to ETC
H cleaved off NADH & FADH2
electrons stripped from H atoms H+ (protons) electrons passed from one electron carrier to next in
mitochondrial membrane (ETC) flowing electrons = energy to do work
transport proteins in membrane pump H+ (protons) across inner membrane to intermembrane space
ADP+ Pi
TA-DA!!Moving electrons
do the work!
H+ H+ H+
But what “pulls” the electrons down the ETC?
electronsflow downhill
to O2 oxidative phosphorylation
O2
H2O
Electrons flow downhill Electrons move in steps from
carrier to carrier downhill to oxygen each carrier more electronegative controlled oxidation controlled release of energy
make ATPinstead of
fire!
H+
ADP + Pi
H+H+
H+
H+ H+
H+H+H+We did it!
ATP
Set up a H+
gradient Allow the protons
to flow through ATP synthase
Synthesizes ATP
ADP + Pi ATP
Are wethere yet?
“proton-motive” force
The diffusion of ions across a membrane build up of proton gradient just so H+ could flow
through ATP synthase enzyme to build ATP
Chemiosmosis
Chemiosmosis links the Electron Transport Chain to ATP synthesis
Chemiosmosis links the Electron Transport Chain to ATP synthesis
So that’sthe point!
Peter Mitchell Proposed chemiosmotic hypothesis
revolutionary idea at the time
1961 | 1978
1920-1992
proton motive force
H+
H+
O2+
Q C
ATP
Pyruvate fromcytoplasm
Electrontransportsystem
ATPsynthase
H2O
CO2
Krebscycle
Intermembranespace
Innermitochondrialmembrane
1. Electrons are harvested and carried to the transport system.
2. Electrons provide energy
to pump protons across the membrane.
3. Oxygen joins with protons to form water.
2H+
NADH
NADH
Acetyl-CoA
FADH2
ATP
4. Protons diffuse back indown their concentrationgradient, driving the synthesis of ATP.
Mitochondrial matrix
21
H+
H+
O2
H+
e-
e-
e-
e-
ATP
Cellular respiration
2 ATP 2 ATP ~36 ATP+ +
~40 ATP
Summary of cellular respiration
Where did the glucose come from? Where did the O2 come from? Where did the CO2 come from? Where did the CO2 go? Where did the H2O come from? Where did the ATP come from? What else is produced that is not listed
in this equation? Why do we breathe?
C6H12O6 6O2 6CO2 6H2O ~40 ATP+ + +
ETC backs up nothing to pull electrons down chain NADH & FADH2 can’t unload H
ATP production ceases cells run out of energy and you die!
Taking it beyond… What is the final electron acceptor in
Electron Transport Chain?
O2
So what happens if O2 unavailable?
NAD+
Q
C
NADH H2O
H+
e–
2H+ + O2
H+H+
e–FADH2
12
NADH dehydrogenase
cytochrome bc complex
cytochrome coxidase complex
FAD
e–
2006-2007
What’s thepoint?
The pointis to make
ATP!
ATP
Respiratory substrates Glucose – primary substrate Lipids & amino acids also can be used Energy values of substrates
Carbohydrates - 15.8 kJ/g Lipids - 39.4 kJ/g Protiens - 17.0 kJ/g
So then why don’t we use fats for energy, they have the greatest value?
THE RESPIRATORY QUOTIENT Animal cells obtain energy in the form
of ATP by oxidizing food molecules through the process of respiration.
Respiration in animal cells depends on oxygen.
Electrons from the chemical bonds of the fuel source combine with oxygen and hydrogen ions to form water and carbon dioxide.
Questions How can we quantify metabolism? How does the energy source affect the
volume of O2 consumed and volume of CO2 produced?
How do they differ among animals and how are they affected by environmental conditions?
THE RESPIRATORY QUOTIENT One ratio that is particularly useful for
understanding animal metabolism is the respiratory quotient.
The respiratory quotient (RQ) measures the ratio of the volume of carbon
dioxide (Vc) produced by an organism
to the volume of oxygen consumed (Vo).
RQ = Vc/Vo This quotient is useful because the
volumes of CO2 and O2 produced depends on which fuel source is being metabolized. Measuring RQ is a convenient way to gain information about the source of energy an animal is using. We can then compare the metabolism of animals under different environmental conditions by simply comparing RQ.
RQ Carbohydrates, such as glucose, are an
important source of fuel. The general formula for a carbohydrate is CnH2nOn. For example, if we take n = 6 we have the formula for glucose, C6H12O6.
We can describe the metabolic reaction of a carbohydrate by the following equation:
CnH2nOn + nO2 --> nCO2 + nH2O
RQ n=6
CnH2nOn + nO2 --> nCO2 + nH2O
C6H12O6 + 6O2 --> 6CO2 + 6H2O
Now compare the number of molecules of O2 to the molecules of CO2. We have a ratio of 1 to 1, since there are 6 O2 and 6 CO2 molecules.
RQ = Vc/Vo = 6/6 = 1
RQ In humans, the use of fats as a fuel
source is quantitatively more important than glucose. The general formula for a saturated fat is (CH2O)3(CH2)3n(CO2H)3 . For example, if we take n = 17 we have the formula for the fat glycerol tristearate.
C3n+6H6n+9O9 + (4.5n + 3.75)O2 --> (3n + 6)CO2 + (3n + 4.5)H2O
RQ C57H111O9 + 80.25 O2 57 CO2 + 55.5 H2O
RQ = Vc/Vo = 57/80.25 = 0.7 the metabolism of fat consumes a great
deal more oxygen RQ for proteins = 0.9
RQ The respiratory quotient for some
animals can change depending on their activity. At rest, a Desert Locust has an RQ of about 1.0. During flight, however, the RQ decreases to about 0.7. How would you interpret this?
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