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CBB 20303BIOCHEMISTRY
Cellular Respiration
(Electron Transport Chain)By
Muhammad Noor Azhre Shah B. Malek Razuan55202113051
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Introduction
All living organisms required energy for theactivities of life, for example, movement,maintenance of body temperature, growth andreproduction.
Cellular respiration can be defined as complexprocess in which food molecules or organicmolecules are broken down to harvest chemicalenergy which is then stored in the chemicalbonds of Adenosine triphosphate (ATP)
*ATP= the energy currency in cells any organism.
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Electron Transport Chain
ETC is under aerobic respiration in stages 4metabolic pathway in Oxidative phosphorilation.
Oxidative phosphorilation is electron produced
from glycolysis and the Kreb cycle are passedalong a series of enzymes embedded in theinner mitochondrial membrane, producing ATPvia oxidative phosphorilation and
Chemiosmosis. Most energy locked in theoriginal glucose molecule will be released by theelectron transport chain and chemiosmosis
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ETC is a network of electron carrying proteins located in the folds of the inner membrane(cristae) of the mitochondria.
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The electron carriers in the electron transportchain can be divided into two group:
A) Complexes consisting of integral membraneproteins which act carrier proteins as well asproton pumps.I. NADH dehydrogenase or NADH-Q reductase (complex 1)II.Cytochrome reductase or cytochrome b-c1 complex
(complex III)III.Cytochrome oxidase or cytochrome a-a3 complex
(complex IV)
B) Mobile carrier that shuttle the electronsbetween the three proton pumpsI. Ubiquinone or coenzyme Q (CoQ)II.Cytochrome c (cyt c)
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The electron carriers of the electrontransport chain are embedded in the innermitochondrial membrane and necessaryfor oxidative phosphorylation.
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Electron Transport Chain
intermembranespace
mitochondrialmatrix
inner
mitochondrialmembrane
NAD +
Q
C
NADH H2O
H+
e
2H + + O 2
H+ H+
e FADH 2
12
NADHdehydrogenase
cytochrome b c complex
cytochrome coxidase complex
FAD
e
H
H e- + H +
NADH NAD + + H
H
pe
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But what pulls theelectrons down the ETC?
electronsflow downhill
to O 2 oxidative phosphorylation
O 2
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Electrons flow downhill
Electrons move in steps fromcarrier to carrier downhill to O2
each carrier more electronegative
controlled oxidationcontrolled release of energy
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Complex I
Complex III
Complex IV
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Step 1
NADH from the Krebs Cycle will interactwith Complex I contains a coenzyme,Flavin mononucleotide( FMN ), and iron-sulphur ( Fe.S ) proteins. Electrons from
NADH will cause FMN to reduce to FMNH 2 and NADH is oxidise to NAD + by oxygenas the oxygen is reduce to water.This reaction release a great deal ofenergy and the energy is used to pumpprotons into the intermembrane space ofmitochondrion.
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Complex I
Complex III
Complex IV
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Step 2
Electrons from the reduced complex I arethen passed to coenzyme Q( CoQ ).This cause CoQ to be reduce to CoQH 2
and complex I oxidised.CoQ is small and lipid-soluble. It is mobile in the lipid bilayer and diffuses easily. Itshuttles the electrons to complex III.
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Step 3
CoQH 2 passes the electrons to complex IIIcausing the complex III to be reduce andCoQH 2 to be oxidised back to CoQ.
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Complex I
Complex III
Complex IV
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Step 4
Cytochrome c (cyt c) is another smallmobile protein. it accepts electrons fromcomplex III and become reduced. Cyt cthen shuttles the electrons to the lastelectron acceptor in the elcetron transportchain, complex IV
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Complex I
Complex III
Complex IV
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Step 5
Complex IV contains cytochrome a andcytochrome a 3. When it accepts electronsfrom cytochrome c, it is reduced andcytochrome c is oxidised. The electronsare eventually transferred to oxygen whichis reduced to water.
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AP Biology H+
ADP + P i
H+ H+
H+
H+ H+
H+ H+ H+
ATP Synthase Complex
ATP
Set up a H +gradientAllow the protons
to flow throughATP synthaseSynthesizes ATP
ADP + P i ATP
proton -motive force
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The ETC accomplishes the following:
Stepwise transfer of electron from NADH ( andFADH 2) to oxygen molecules to form watermolecules. Harnesses the energy released by this transfer topump protons (H +) from the matrix to theintermembrane space of mitochondrion.Formation of a proton gradient across theinner membrane. The protons will diffuse downthis gradient and re-enter the matrix throughanother complex consisting of integral proteins inthe inner space membrane. This complex isknown as the ATP synthase.
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Video
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The diffusion of ions across a membranebuild up of proton gradient just so H+ could flow
through ATP synthase enzyme to build ATP
Chemiosmosis
Chemiosmosis links the ElectronTransport Chainto ATP synthesis
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References
Murray, Robert K.; Daryl K. Granner,Peter A. Mayes, Victor W. Rodwell (2003).Harper's Illustrated Biochemistry. NewYork, NY: Lange Medical Books/ MgGrawHill. p. 96 Karp, Gerald (2008). Cell and MolecularBiology (5th ed.). Hoboken, NJ: JohnWiley & Sons. p. 194