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Understanding Oxidative Phosphorylation: The Role of Electron Transport and ATP Synthesis, Lecture notes of Biochemistry

An outline of oxidative phosphorylation, focusing on the function of the electron transport chain in making water and synthesizing ATP in mitochondria. It includes discussions on the energy of reduced cofactors, the structure of mitochondria, and the importance of proton motive force. Calculations are included to determine the energy available from NADH and FADH2 for ATP synthesis.

What you will learn

  • How does the electron transport chain contribute to the synthesis of ATP during oxidative phosphorylation?
  • What is the role of the proton motive force in ATP synthesis?
  • How much energy is available from NADH and FADH2 for ATP synthesis?

Typology: Lecture notes

2021/2022

Uploaded on 09/12/2022

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BI/CH 422/622 on 2/22/22
OUTLINE:
Glycogenolysis
Glycolysis
Other sugars
Paste ur: Anae robic vs Aerob ic
Fermentations
Pyruvate
pyruvate dehydrogenase (ox-decarbox; S-ester)
Krebs’ Cycle
How did he figure it out?
Overview
8 Steps
Citrate Synthase (CC)
Aconitase (=, -OH)
Isocitrate dehydrogenase (ox-decarbox; =O)
Ketoglutarate dehydrogenase (ox-decarbox; S-ester)
Succinyl-CoA synthetase (sub-level phos)
Succinate dehydrogenase (=)
Fumarase ( -OH)
Malate dehydrogenase (=O)
Energetics
Regulation
Summary
Oxidative Phosphorylation
Energetics
Mitochondria
Tran sp or t
Electron transport
Discovery
Fou r Com plexes
Exam-1 material
Exam-2 material
Oxidative
Phosphorylation
pf3
pf4
pf5
pf8
pf9

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Download Understanding Oxidative Phosphorylation: The Role of Electron Transport and ATP Synthesis and more Lecture notes Biochemistry in PDF only on Docsity!

BI/CH 422/622 on 2/22/

OUTLINE:

GlycogenolysisGlycolysis Other sugarsPasteur: Anaerobic vs Aerobic Fermentations Pyruvate (^) pyruvate dehydrogenase (ox-decarbox; S-ester) Krebs’ CycleHow did he figure it out? Overview8 Steps Citrate Synthase (C–C)Aconitase ( = , -OH) Isocitrate dehydrogenase (ox-decarbox; =O)Ketoglutarate dehydrogenase (ox-decarbox; S-ester) Succinyl-CoA synthetaseSuccinate dehydrogenase (sub-level phos)( = ) FumaraseMalate dehydrogenase ( -OH) (=O) EnergeticsRegulation Summary Oxidative Phosphorylation EnergeticsMitochondria TransportElectron transport Discovery Four Complexes

Exam-1 material Exam-2 material

Oxidative

Phosphorylation

Oxidative Phosphorylation

  • Function of electron-transport chain in mitochondria…... make water (finish the reaction: C 6 H 12 O 6 + 6O 2 à 6CO 2 + 6H 2 O )
  • Building up the proton-motive force
  • Synthesis of ATP in mitochondria, chloroplasts, & bacteria

Learning goals:

  • Fuels for the cell, in the form of reduced carbon

compounds (sugars), have been burned to carbon

dioxide.

  • Electrons from reduced fuels are transferred to

cofactors, which get reduced as NADH or FADH 2.

  • In oxidative phosphorylation, energy from NADH

and FADH 2 is used to make ATP. …... But how?

6O 2 6H 2 O

Glycogenolysis

Glycolysis

Pyruvate Oxidation

Krebs' Cycle

Oxidative

Phosphorylation

Oxidative Phosphorylation

Energy of the reduced cofactors

Oxidative Phosphorylation

Is there enough energy in NADH & FADH 2 to drive the synthesis of ATP? Each ATP synthesis is about +7.3 kcal/mol (opposite of hydrolysis) We can do this calculation two ways:

  1. Calculate the D E °’^ needed to get 1 ATP made: compare to D E °’^ of NADHàO (^2)
  2. Calculate the D G °^ ^ for the NADHàO 2 : compare to the D G °^ ^ for ATP synthesis

D G °^ ^ = –n F D E °^

D E °’^ = E °’^ ( reduction ) – E °’^ ( oxidation )

= +0.82 V – (–0.32 V)
= +1.14 V

7.2 times more energy in 2e– going from NADH to oxygen than needed to drive the synthesis of ATP

D G °’^ of NADHà ½ O 2 DG °’^ of ATP

D G °^ ^ = –52.6 kcal/mol D G °^ ^ = +7.3 kcal/mol

= –(2)(23.06V-1kcalmol -1)(+1.14V)

6.5 times more energy in 2egoing from FADH – than needed to drive the^2 to oxygen synthesis of ATP

Structure of Mitochondria

Oxidative Phosphorylation

Double membrane leads to fourdistinct compartments:

  1. Outer membrane:– relatively porous membrane; allows passage of metabolites
  2. Intermembrane space (IMS):– similar environment to cytosol
    • higher proton concentration(lower pH)
  3. Inner membrane– relatively impermeable, with
    • proton gradient across itlocation of electron transport
    • chain complexesConvolutions called cristae serve to increase the surface area.
  4. Matrix– location of the citric acid cycle and parts of lipid and amino-acidmetabolism
    • lower proton concentration(higher pH)

+++++


cow artery endothelial cell

cow heart muscle

cow liver

D! ≈ –0.06 V

  • These translocases cost the membrane potential, which must be restored; costs 25% of Electron Transport.
  • These translocases require energy from both the electrochemical gradient across inner mitochondrial membrane plus the proton gradient. Together they are called the Proton Motive Force.
  • What generates this gradient?
  • How much energy does it take to pump H +^ out?

Oxidative Phosphorylation

D! ≈ –0.06 V

This antiporter works muchlike GLUT1. The import of ADP and export of ATP isfavored by 1) the [ATP] concentrations, and 2) thecharge difference.

0

This symporter has to combatthe charge difference of P to a more negative space, but its i^ going favored by the overwhelminghigh [H +] and [P i ] on the outside.

14% of protein in theinner membrane is the ADP/ATP translocase

Energy required to pump a single proton against a pH gradient

[H +in]

[H +out ] H +in ⇌ H +out

D

So, if its more negative And, if its more positive

As a consequence, it will take ~3 protons per ATP.

Oxidative Phosphorylation

D G^ ’^ = RT ln ____[H^ + z F D"

  • (^) ]out [H +^ ]in

pHin ≈ 7.

pHout ≈ 6.

ln[H +]out = 2.3log[H +]out = -2.3 pH (^) out ln(1/[H +]in) = 2.3-log[H +]in = +2.3 pH (^) in

= RT2.3(pH (^) in – pH (^) out ) = 5.9(7.5 – 6.75) = 5.9(0.75) = 4.4 kJ/mol = 1.0 kcal/mol

= z F D" = (+1)(96480) D" = (+1)(96480)(+0.06) = 5.8 kJ/mol = 1.4 kcal/mol

Switch the sign herebecause reaction is opposite that of transport

D G^ ’^ = 1.0 + 1.4 = 2.4 kcal/mol

+++++


Top

Bottom

D" ≈ –0.06 V

  • When it was realized that isolated mitochondria are capable of respiration (oxygen consumption when provided fuels), biochemists began purifying them and their components.
  • The first things purified were redox compounds and small stable proteins: - – NADHflavin mononucleotide (FMN) - flavin adenine dinucleotide (FAD)(bound to protein; flavoproteins) - iron-sulfur clusters - – Coenzyme Q (Ubiquinol)cytochromes a , b , or c
  • Once purified, they were analyzed by mea-

suring their E °’.

  • Order of transfer of electrons is dependent

on E °’^ :

Electron Transport Electron-Transport Chain Complexes Contain a Series of Electron Carriers

Big Drop! FAD-E + 2 H^ +^ + 2e– à^ FADH^2 -E^ FeS –0. Big Drop!

Big Drop!

  • NAD+^ , FMN, and FAD accept electrons. The flavin nucleotides can accept one or two electrons, and can also donate one electron at a time to acceptors that can only accept single electrons
  • Ubiquinone, also called Coenzyme Q, is an isoprene lipid that readily accepts electrons. Upon accepting two electrons, it picks up two protons to give an alcohol, ubiquinol (CoQH 2 ). Its found IN the inner membrane.
  • Iron-sulfur complexes (Fe-S) that can only carry one electron at a time (role is different than in aconitase).

Electron Transport

Cytochromes

  • Small one-electron carrier proteins
  • Iron-coordinating porphyrin-ring derivatives
  • b / b 1 , c, or a/a 3 differ by ring additions

Electron Transport Cytochromes

  • Mobile electron carrier; a peripheral membrane protein - Cytochromeintermembrane space (IMS). c moves through the
  • A soluble heme-containing protein
  • Heme iron can be either ferrous (Fe 2+^ , reduced) or ferric (Fe 3+^ , oxidized).
  • Cytochrome c carries a single electron.
  • The two redox forms have different spectra:

Electron Transport

Cytochrome c

  • Intense Soret band near 400 nm absorbs blue light and gives cytochrome c an intense red color.