Step 1: Complex I - NADH-Q reductase - 2 electrons from NADH (H+) are transferred to FMN - NADH is converted back to NAD+ - FMNH2 transfers 2 electrons to sets of Fe-S clusters - 2 electrons are transferred to coenzyme Q reducing it to QH2 - Process cause 4 H+ from matrix to move to inter membrane - H+ cannot diffuse back into matrix creating a proton gradient

Step 2: Complex II – Succinate dehydrogenase - FADH2 is oxidised and loses two electrons to coenzyme Q via Fe-S clusters - Does not pump H+ = less ATP from FADH2 compared to NADH

Step 4: Complex III – Q-cytochrome c oxidoreductase - Complex iii catalyses the transfer of four electrons from 2 QH2 - For each 2 electrons transferred from QH2, two H+ pass into the intermembrane space and one is donated to Q from the matrix and the other is donated to CytC.

Oxidative Phosphorylation: The Electron Transport Chain Flashcards by KJ Hall

Where does the reducing power/electrons go?

The two mitochondrial membranes are separated by the intermembrane compartment

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What is oxidative phosphorylation?

Process in which ATP is formed as a result of the transfer of electrons from NADH or FADH2 to oxygen (O2) by a series of electron carriers

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What is the electron transfer chain?

A specialised set of protein complexes and electron carriers

Where three protein complexes span the membrane, one is located on the matrix side only

Two highly mobile electron carriers shuttle electrons

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What shuttles electrons in oxidative phosphorylation?

Two highly mobile electron carries

Q and cyt c

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Does the electron transfer go up or down the free energy gradient?

Down

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Fill in the gap:

Each complex/carrier in the chain has a …… free energy than the preceeding member.

lower

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Do electrons flow spontaneously or on purpose along the electron transfer chain?

spontaneously

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How do electrons generate ATP energy?

Electron-motive force is converted into a proton motive force
Proton motive force is converted into phosphoryl transfer potential

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How many steps are there in the oxidative phosphorylation?

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What is step 1?

Step 1: Complex I - NADH-Q reductase

2 electrons from NADH (H+) are transferred to FMN
NADH is converted back to NAD+
FMNH2 transfers 2 electrons to sets of Fe-S clusters
2 electrons are transferred to coenzyme Q reducing it to QH2
Process cause 4 H+ from matrix to move to inter membrane
H+ cannot diffuse back into matrix creating a proton gradient

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Describe NADH-Q reductase:

Enzyme consisting of 34 polypeptides
Structure determined by EM at 22A resolution
Membrane spanning part and long arm extended into matrix

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What prothetic groups are in NADH-Q reductase?

Flavin mononucleotide (FMN)

- Iron-sulphur clusters (Fe-S)

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What is step 2?

Step 2: Complex II – Succinate dehydrogenase

FADH2 is oxidised and loses two electrons to coenzyme Q via Fe-S clusters
Does not pump H+ = less ATP from FADH2 compared to NADH

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What is Succinate dehydrogenase bound to?

the inner mitochondrial membrane

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What is step 3?

Step 3: Coenzyme Q

Q can accept 2 electrons from either Complex I (NADH) or Complex II (FADH2) to become QH2 and transfers them to complex III

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What is another name for Coenzyme Q?

ubiquinone

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What is coenzyme Q?

Q is hydrophobic and diffuses rapidly within the inner mitochondrial membrane

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What is step 4?

Step 4: Complex III – Q-cytochrome c oxidoreductase

Complex iii catalyses the transfer of four electrons from 2 QH2
For each 2 electrons transferred from QH2, two H+ pass into the intermembrane space and one is donated to Q from the matrix and the other is donated to CytC.

What is complex III?

-Homo-dimer with 11 distinct polypeptide chains.

Contains heme prosthetic groups (Fe3+—> Fe2+)

What are the 4 electrons which is catalysed for transfer by complex III?

Electron 1: CytC
Electron 2: Q
Electron 3: CytC
Electron 4: QH2

what is step 5?

Step 5: Cytochrome c

-Carries one electron from Q-cytochrome c oxidoreductase to cytochrome c oxidase (IV)

What is Cytochrome c?

present in all organisms
mitochondrial respiratory chains
has a highly conserved structure
Small soluble protein containing c-type heme

What is step 6?

Step 6: Complex IV - Cytochrome c oxidase

For every NADH molecule that enters the chain, 2 x cyt c transfer 2 electrons to oxygen
Splitting of O2 to generate 2H20 requires 4 protons and 4 electrons
Requires 2 x NADH
Results in 4H+ translocated into inter membrane space

What is complex IV?

13 polypeptide chains
Two heme groups (Fea3+ and Fea32+)
Contains two copper ions (CuB1+,CuA2+)
Contains redux centres

Overview of the oxidative phosphorylation:

Three of our complexes are proton pumps: using electrons to pump H+ into the intermembrane space

How does oxidative phosphorylation create a proton gradient?

- Protons pumped across this membrane as electron flow through respiratory chain - Generates a pH and electrical gradient

What route muse protons go through to get back into the matrix?

Through ATP synthase

What are oxidation and ATP synthesis coupled by?

Transmembrane proton movement

What is Complex V - ATP synthase?

A complex of many subunits forming a head, stalk and a transmembrane pore - F1 catalytic subunit - F0 proton-conducting subunit

What is the F1 catalytic subunit of Complex V - ATP synthase?

- Extends into the matrix - Five types of polypeptide chains: α3, β3, γ, δ and ε - The majority of F1 consists of α3, β3 subunits

What is F0 proton-conducting subunit f Complex V - ATP synthase?

- Hydrophobic - spans the inner mitochondrial membrane - Contains the proton channel of the complex - This channel consists of 10 c subunits forming a pore and an a subunit

Can ATP be formed without the flows of H+ through the ATP synthase complex?

Yes

What is the problem of ATP be formed without the flows of H+ through the ATP synthase complex?

ATP does not leave the catalytic site of the enzyme unless H+ flow through the pore

Fill in the gap: | H+ ..... the ATP

Releases

What is the final outcome of metabolism?

1 NADH = 10 H+ translocated = 2.5 ATP 1 FADH2 = 6 H+ translocated = 1.5 ATP Total yield = 30 to 32

What are the inhibitors of oxidative phosphorylation?

- Rotenone: Insecticide (made by plants) - Amytal: Barbiturate - Antimycin A: produced by Streptomyces

What inhibitors out of Rotenone, Amytal and Antimycin A act between Complex I and Q?

Rotenone and Amytal

What inhibitors out of Rotenone, Amytal and Antimycin A act between Complex Q and III?

Antimycin A

What are the inhibitor for Cytochrome c?

Cyanide | Carbon monoxide

What is are uncoupling proteins?

The tight coupling of electron transport and oxidative phosphorylation can be disrupted These allow protons to flow back across the membrane without going through ATP synthase. ‘Proton leak’

What do synthetic uncouples increase?

Permeability of the inner mitochondrial membrane to protons

What else uses proton motive force?

Bacteria

Where does bacterial electron transport chain take place?

Inner membrane

What does the proton gradient drive?

Rotation of flagella basal body