Ox Phos - Mitochondria Flashcards

1
Q

Where does oxidative phosphorylation take place?

A

In the inner mitochondrial membrane

- matrix above and inner membrane space underneath

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2
Q

What is the function of the mitochondrial respiratory chain?

A
  • to pump H+ across the inner mitochondrial membrane and generate a proton electrochemical gradient (Δp)
  • a substantial Δp is generated
  • enough Δp to drive H+ back across the membrane through ATP synthase, causing production of ATP
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3
Q

How many protons are picked up from the matrix for every 2 electrons?

A

every 2 electrons = 10 protons

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4
Q

What happens at complex I?

A
  1. NADH diffuses through the matrix until it encounters Complex I
  2. Oxidation of NADH by FMN.
    - Semiquinone state of FMN enables a change from 2e- to 1e- transfers
    - NADH -> NAD+ + H+
  3. Transfer of e- one at a time, down a “wire” consisting of ~7 FeS clusters
  4. The e- down the cluster reduces Quinone
    - made possible by semiquinone intermediate
    - 2H+ + UQ -> UQH2
  5. Fully reduced UQH2 dissociates from complex I, diffusing within the hydrophobic fatty acid side-chains of the phospholipid
    - creates a UQ pool
    - eventually will encounter Complex III
  6. E- transfer through complex I is coupled to translocation of 4H+ across the inner mitochondrial membrane, contributing to the Δp
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5
Q

What is the structure of complex I?

A

4 subunits
Another subunit potruding onto the matrix side which has Flavin (FMN) and also where NADH binds and UQ gets reduced
Long alpha helix
- repeating conformational changes in the first unit so that other protons can be diffused through easier
- positive induction

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6
Q

What happens at complex III/ during the Q cycle?

A
  1. Reduced quinone (UQH2) arrive at quinone binding site
    - Can give up one e at a time or both at once
    - 1 e transfers to iron sulfur cluster
    - Then goes to a cytochrome called Heme c1 and then to cytochrome c (inside the mitochondrial space)
    - 2nd e- transfers onto heme bl
    - Onto bh and then onto another Quinone
    - Reducing the Q (leaving radical, Q dot)
    Overall reduced cytochrome c & one reduced quinone close to matrix space
  2. A second UQH2 attaches to the quinone binding site
    - One e follows 1st path again & reduces cytochrome c
    - Another e follows the other pathway and reduces the other quinone near the matrix
    Overall reducing one Quinone, 2 cytochrome c’s and pulling 2 protons
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7
Q

What is the structure of complex III?

A

multi-polypeptide transmembrane protein

  • 3 Haems
  • 2 Iron sulphurs
  • 2UQ-binding sites per monomer
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8
Q

How many cyt c’s are reduced per UQH2 in complex III?

A

2

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9
Q

Why do the two electrons go to 2 different pathways when being donated by UQH2 in Complex III?

A

FeS behaves like a pendulum (swinging backwards and forwards) - picking up the first electron and then swinging to the second position
- As the e is being dropped off at the second position (cytochrome c1) the distance is larger and less competitive than the alternate pathway for the second e and so it goes on the alternate route

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10
Q

Why does the 1st electron go through that specific pathway in the Q cycle?

A

1st e goes through the pathway due to:

  • Distance of FeS, Cytochrome c1 and cytochrome c are shorter
  • Mid-point potentials give the blue path a more competitive rate
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11
Q

Why does the 2nd electron go through the alternate pathway in the Q cycle?

A

2nd e goes through alternate path due to:

- going from a lower Em to a higher Em

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12
Q

What is the other name for complex III?

A

cytochrome bc1

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13
Q

What is the other name for complex IV?

A

cytochrome aa3

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14
Q

What happens at complex IV?

A
  1. 4 cyt c delivering 4 e-
    complex has 2 copper atoms - bound to polypeptides in a binuclear copper site
  2. E’s arrive to copper one at a time
  3. Hop to Haem a3
  4. Then transfers onto CuB/Haema3 centre
  5. O2 binds next to the complex and is reduced to O2 2-
  6. Further reduced to 2H2O (by two more cyt c and 4H+ from matrix)
  7. Coupled to the O2 reduction, 2H+ are pumped across membrane per 1/2O2
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15
Q

Where does Oxygen bind in complex IV?

A

Between Haem a3 & CuB

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16
Q

What is the overall Oxidative Phosphorylation reaction?

A

2Cytc (red) + 1/2O2 + 4H+ -> 2Cytc (ox) +H2O + 2H+

17
Q

What is complex II used for?

A
  • links Krebs cycle with Ox.Phos - alternate pathway into the ETC
  • starts at a lower point in energy
  • provides an extra source of electrons into the respiratory chain
  • not a proton pump
18
Q

How are electrons introduced to the ETC from complex II?

A

mitochondrial succinate DH catalyses the step of turning succinate to fumarate

  • the 2e- go down a series of FeS clusters
  • can reduce Quinone
19
Q

What is the structure of Complex II?

A
  • flavin binding site
  • FeS clusters
  • Quinone Binding site in the membrane
20
Q

How can a bacteria respire on fumarate?

A

similar to complex II but operates in opposite way
- Electrons are going up the chain to fumarate
- Neighbour proteins produce the e’s that feed up to fumarate
Proton gradient is still made