Mitochondrial respiratory chain Flashcards

1
Q

How permeable is the outer membrane of the mitochondria?

A

Freely permeable to small molecules and ions

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2
Q

How permeable is the inner membrane of the mitochondria?

A

Impermeable to small molecules and ions, including H+

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3
Q

Where is the electron transport chain located?

A

On the inner mitochondrial membrane

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4
Q

Describe what happens at complex 1

A

Initially electrons are passed to FMN to produce FMNH2
Subsequently transfer to a series of iron-sulphur clusters
Then transfer to Coenzyme Q, or ubiquinone
So, the enzyme catalyses the overall reaction:
NADH + H+ + Q = NAD+ + QH2
It is a proton pump, moving protons from the matrix into the intramitochondrial space

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5
Q

What is the overall function of complex 1?

A

Acceptor of electrons from NADH

Moves 4 H+ions from matric to space between the two membranes- proton pump

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6
Q

Describe what happens at complex 2

A

Succinate is converted to fumarate by succinate dehydrogenase
Electrons of FADH2 pass on their electrons to complex II
Complex II passes them to ubiquinone

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7
Q

How do other substrates for mitochondrial dehydrogenase pass their electrons to ubiquinone?

A

Straight to ubiquinone

No need for the complexes 1 or 2

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8
Q

Describe the action of complex 3

A

Ubiquinone: cytochrome c oxidoreductase
Second of three proton pumps in the respiratory chain
Carries 4 H+

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9
Q

Describe the action of complex 4

A

Cytochrome oxidase
Third and final proton pump- carries 2 H+
Carries electrons from cytochrome c to molecular oxygen
Produces water

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10
Q

Which complex is not a proton pump?

A

Complex 2

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11
Q

Why is oxygen important for the respiratory electron chain?

A

Acts as a final electron acceptor

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12
Q

How are the protons pumped?

A

From energy harnessed from the acceptance of electrons at various points
Conservation of energy- holding energy till the right time to make the ATP

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13
Q

What are the 3 specific systems in the inner mitochondrial membrane that allow movement across the membrane?

A

Transport ADP and Pi into the matrix
Synthesise ATP
Transport ATP into the cytosol

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14
Q

State the equation for the synthesis of ATP

Give the actual substrates

A

ADP3- + Pi2- + H+ ——–> ATP4- + H2O

Actual substrates are the Mg2+ complexes of ADP and ATP

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15
Q

Give the number of negative charges of ADP and ATP in the physiological pH range

A

ATP has 4 negative charges and ADP has 3 negative charges

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16
Q

Describe the Adenine nucleotide translocase

A

Integral protein of the inner mitochondrial membrane
Transports ADP3- from the intramitochondrial membrane space into the matrix
In exchange for an ATP4- molecule
transported in the other direction
(Favoured by the proton pump)
Known as an ‘antiporter’

17
Q

Give the name of a specific inhibitor of adenine nucleotide translocase

A

Atractyloside, a glycoside isolated from a thistle

18
Q

Describe phosphate translocase

A

A second membrane transport is essential for oxidative phosphorylation and synthesis of ATP
Transports both phosphate and hydrogen ions into the matrix: a ‘symporter’ - favoured by the transmembrane proton gradient

19
Q

What is a symporter?

A

2 things brought in via the same direction

20
Q

What is an antiporter?

A

One thing in and one thing out

21
Q

What are the two functional domains of ATP synthase?

A

Fo, an oligomycin-sensitive proton channel

F1, an ATP synthase

22
Q

Describe the subunit structure of F0

A

Fo comprises three different types of subunit: a, b, and c
Forms a complex of 13-15 subunits
Subunits c1-10 arranged in a circle

23
Q

Describe the subunit structure of F1

A

F1 comprises five different types of subunit: alpha3, beta3, gamma, delta, and epsilon

Forms a complex of 9 subunits

24
Q

What is special about the 3 beta subunits of F1?

A

The 3 beta subunits have catalytic sites for ATP synthesis

25
Describe the structure of ATP synthase
- beta subunits are arranged alternately with alpha subunits like segments of an orange - Form a knob-like structure held by a stalk of the gamma and epsilon subunits - delta subunit interacts with the two ‘b’ subunits of Fo
26
Describe the theory of rotational catalysis
3 beta subunits take it in turns catalysing the synthesis of ATP Any given beta subunit starts in a conformation for binding ADP and Pi Then changes conformation so the active site now binds the product ATP tightly Then changes conformation to give the active site a very low affinity for ATP (‘beta-empty’ conformation) so ATP is released
27
What happens when the gamma unit rotates?
The gamma-unit rotates, and the properties of the beta-catalytic units change
28
Is the reaction in the respiratory electron chain endergonic or exergonic?
Highly exergonic reaction
29
Give the overall equation of the respiratory electron chain in terms of NADH
NADH + H+ + ½ O2 -------> NAD+ + H2O
30
Describe the energy changes in this reaction
Energy released is coupled to the movement of H+ across the inner membrane Electrochemical energy generated represents temporary conservation of the energy of electron transfer Protons flow spontaneously down their electrochemical gradient releasing energy available to do work
31
Describe uncoupling reagents and their purpose
Normally e- flow and phosphorylation are tightly coupled Uncouplers dissipate the pH gradient by transporting H+ back into the matrix of the mitochondria so bypassing the ATP synthase Thus an uncoupler (e.g. DNP) severs the link between e- flow and ATP synthesis, with the energy being released as heat Can occur naturally e.g. UCP1 (thermogenin) is found in brown adipose tissue and has a specific H+ channel through which the [H+] may be dissipated - energy released as heat
32
Describe brown adipose tissue
``` Brown adipose tissue (BAT): Specialized for heat generation High numbers of mitochondria Mitochondria contain thermogenin (UCP-1) Important in new-borns, possible role in obesity/diabetes ```
33
What is the energy yield from oxidation of 1 molecule of glucose
30 or 32 | Depending on the shuttle G-3 P or malate-aspartate used
34
What is DNP?
Weak acid that crosses membranes 'ferrying' H+ across Each DNP molecule collects a proton from the IMS and moves through the membrane with it, depositing it in the matrix Can then return though the membrane to collect another proton