etc (electron transport chain)

8/13/2019 Etc (Electron Transport Chain)

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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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AP Biology

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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AP Biology

But what pulls theelectrons down the ETC?

electronsflow downhill

to O 2 oxidative phosphorylation

O 2


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AP Biology

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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AP Biology

Complex I

Complex III

Complex IV


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AP Biology

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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AP Biology

Complex I

Complex III

Complex IV


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AP Biology

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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AP Biology

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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AP Biology

Complex I

Complex III

Complex IV


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AP Biology

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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AP Biology

Complex I

Complex III

Complex IV


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AP Biology

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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AP Biology

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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AP Biology

Video


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AP Biology

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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AP Biology

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

etc (electron transport chain)

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