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BCM210 > Topic 14 - Electron Transport Chain > Flashcards

Topic 14 - Electron Transport Chain Flashcards

1
Q

In the ETC, electrons are transferred from …../….. to …….. forming …….

A

In the ETC, electrons are transferred from NADH/FADH2 to O2 forming H2O

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2
Q

Where is the ETC located?

What kind of gradient does it create?

What is this gradient used for?

A
  • Located in the inner mitochondrial memberane (IMM)
  • Creates a proton gradient
  • Used to form ATP
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3
Q

When speaking of oxidative phosphorylation, what does this refer to in terms of the ETC?

A

NADH/FADH2 is oxidised back to NAD+/FAD

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4
Q

Introduction

Give a brief overview of the ETC

A
  • Occurs in IMM
  • e from NADH/FADH2 transferred along chain to O2
  • Exergonic transfer of e is coupled w/ endergonic pumping of p to intermembrane space (IMS)
  • P move down their gradient back to matrix. This exergonic process is coupled w/ endergonic synthesis of ATP from ADP and Pi
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5
Q

_*Describe the range of electron carriers present in_ mitochondria and how they are organised into complexes

Describe complex I

A

Catalyses e transfer from NADH => Q

  • Contains FMN & Fe-S centers (non-haem iron protein) => transfer e
  • Catalyses 2 simultaneous & coupled processes:
  • -Exergonic* transfer of 2 e from ***NADH=>CoQ
  • Endergonictransfer of4 p*** out of matrix => IMS
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6
Q

_*Describe the range of electron carriers present in mitochondria and how they are organised into complexes_

Describe complex II

A

FADH2=>CoQ

  • Complex II = succinate DH complex
  • Catalyses rxn 6 of CA cycle (succinate=>fumarate, which generates FADH2)
  • Catalyses oxidation of succinate=>fumarate, e transferred to FAD (reduced to FADH2)
  • e then passed to CoQ
  • DOES NOT PUMP PROTONS
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7
Q

_*Describe the range of electron carriers present in mitochondria and how they are organised into complexes_

Descrine complex III

A
  • Couples transfer of 2 e from CoQ to Cyt.C (exergonic) w/ transport of 4 p from matrix=>IMS (endergonic)
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8
Q

_*Describe the range of electron carriers present in mitochondria and how they are organised into complexes_

Describe complex IV

A
  • 2 coupled processes
  • transfer of e from Cyt.C=>Oxygen, reducing it to water (exergonic) :: aerobic respo!
  • transport of 2 H+ ions to IMS (endergonic)
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9
Q

_*Describe the range of electron carriers present in mitochondria and how they are organised into complexes_

Name the e carriers w/in and b/w complexes

A
  • NAD+
  • FAD & FMN
  • Non-haem iron proteins
  • Coenzyme Q
  • Cytochromes
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10
Q

*Describe the range of electron carriers present in mitochondria and how they are organised into complexes

Describe the e carrier:
non-haem iron protein

A
  • Normally associated w/ FAD & FMN. Iron carries e by cycling b/w Fe2+ and Fe3+ oxidation states
  • Unlike cytochromes, iron bound directly to protein through cysteine side chains
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11
Q

_*Describe the range of electron carriers present in mitochondria and how they are organised into complexes_

Describe the e carrier:
Coenzyme Q

A
  • Accepts e from:
  • NADH (CI), FADH2 (CII)
  • Glycerol 3P
  • Fatty acyl-CoA
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12
Q

_*Describe the range of electron carriers present in mitochondria and how they are organised into complexes_

Describe the e carrier: Cytochromes (cytochrome C)

A
  • Iron contained in haem group is e carrier
  • Cycles b/w Fe2+ and Fe3+
  • 5 diff. cytochromes, mitochondria have a, b, c
  • Haem group 4x 5 membered nitrogen-containing rings in cyclic structure =>prophyrin
  • 4 N atoms bind to Fe atom
  • Cytochrome C
  • soluble protein of IM space
  • transfers e from CII=>CIV
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13
Q

*Outline the sequence of e carriers

Draw the diagram of e carriers as shown in lecture with labels!!
Dont forget: IMS, p and n, matrix, succinate, fumarate, Cyt C, NADH, NAD+ etc

A
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14
Q

*Describe the effect of e transport inhibitors, uncouplers of e transport & inhibitors of phosphorylation on net ATP synthesis

Describe the effects of Cyanide

A
  • Inhibitor of ETC
  • Binds tightly to FE atom of CIV
  • Blocks e transfer =>oxygen
  • Will block all other complexes as they will all be fully reduced
  • Thus, ATP production stops & important muscle tissue ceases to function
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15
Q

_*Describe the effect of e transport inhibitors, uncouplers of e transport & inhibitors of phosphorylation on net ATP synthesis_

Describe the effects of Oligomycin

A
  • Inhibits ATP synthase
  • Binds to Fo domain
  • Prevents flow of P through domain
  • :: ATP synthesis blocked
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16
Q

_*Describe the effect of e transport inhibitors, uncouplers of e transport & inhibitors of phosphorylation on net ATP synthesis_

Describe the effects of DNP (2,4-Dintrophenol)

A
  • Uncoupling agent
  • Binds to a p in IMS, then diffuses across IMM into matrix, where it releases the p
  • DNP:: disrupts p gradient required for ATP synthesis. Little ATP produced
  • death by overheating!
17
Q

_*Describe the effect of e transport inhibitors, uncouplers of e transport & inhibitors of phosphorylation on net ATP synthesis_

Describe the effects of Thermogenin

A
  • Uncoupling agent (natural)
  • Dissipates p gradient. Inserts itself in membrane & allows flow of H+ that is not coupled to ATP synthesis
  • Allows e transfer to occur but not ATP synthesis
  • Energy dissipated as heat
  • Brown fat! Newborn mammals
18
Q

*Appreciate the role of ‘coupling’ of e transport to phosphorylation of ATP in control of energy yielding processes

*Account for the production of ATP during e transport according to chemiosmotic theory

A
  • e transport results in H transport -pumping of H ions out of matrix
  • Creates proton gradient -protons pass back through IMM through H+ pore in ATP synthase
  • Flow of H+ down [] leads to ATP synthesis -passage of h+ down proton-motive gradient causes a conformational change in 3D structure of ATP synthase, causing synthesus & release of ATP
19
Q

Describe ATP synthase

A
  • Complex V
  • Catalyses formation of ATP
  • attached to IMM
  • two functional domains F0 and F1; both required for ATP synthesis in cell
20
Q

Calculate ATP yields for various substrates, given the stoichiometry of the reactions of these substrates in terms of yields of NADH & FADH2

A
  • 10 protons are pumped per pair electrons from NADH
  • 4 at CI
    -4 at CIII
    -2 at CIV
  • 6 protons are pumped per pair electrons from FADH2
    -4 at CIII
    ​-2 at CIV
  • ~ 4 protons are required to drive synthesis of one ATP molecule ::
    -2.5 ATP are formed from one pair of electrons from NADH
    -1.5 ATP are formed from one pair of electrons from FADH2
21
Q

The chemiosmotic theory

Flow of 2 electrons from NADH through ETC to O2 can be written as?
This net reaction is highly ……
?? kJ/mol?
How many H+ ions are pumped?

A
  • NADH + H+ + 1/2O2 => NAD+ + H2O
  • Highly exergonic
  • -220kJ/mol
  • For each 2 electrons transferred from NADH to O2 through ETC, 10 H+ ions are pumped from matrix to IMS
22
Q

*Describe the role of the malate-aspartate & glycerol 3P shuttles in transport of NADH from the cytoplasm

Describe the process of the malate-aspartate shuttle

A
  • NADH transferred as NADH
  • Generates 2.5 ATP
  • Oxaloacetate on cytoplasmic side is reduced to NADH, creating malate & NAD+
  • Malate & e are transported into mitochondria across IMM, in exchange for a-ketoglutarate, which is transported out of mitochondria
  • Once inside, energy in malate extracted by reducing NAD+ to make NADH, regenerating oxaloacetate
  • This NADH is then free to transfer its high energy e to ETC
23
Q

_*Describe the role of the malate-aspartate & glycerol 3P shuttles in transport of NADH from the cytoplasm_

Describe the process of the glycerol-3P shuttle

A
  • https://www.youtube.com/watchv=ZSS1wsrk5X4
  • NADH entered as FADH2
  • Bypasses CI; generates 1.5 ATP
  • G3P DH converts DHAP to G3P by oxidising 1 molecule of NADH to NAD+
  • G3P gets converted back to DHAP by G3P DH2, this time by reducing 1 molecule of FAD to FADH2
  • FADH2 then reduces CoQ, which enters oxidative phosphorylation
  • Rxn irreversible
24
Q

Regulation of Oxidative Phosphorylation

ADP is major regulator
High ADP=?
Low ADP=?

A
  • High ADP =
  • low energy levels
  • accelerated flow of e through ETC
  • Low ADP =
  • high energy levels
  • reduced flow of e through ETC
25
Q

Regulation points

Energy (ATP) producing pathways are reciprocally regulated.
When ATP high/ADP low=?
When ATP low/ADP high=?

A
  • High ATP/Low ADP
  • glycolysis inhibited
  • CAC inhibited
  • Oxidative phosphorylation inhibited
  • Low ATP/High ADP
  • Glycolysis activated
  • CAC activated
  • Oxidative phosphorylation activated
26
Q
A
  1. 1 and 4 are correct
27
Q
A
  1. Coenzyme A
28
Q
A
  1. Complex II
29
Q

BCM210 (18 decks)

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