Making energy in the mitochondria

What kind of process is getting energy out of sugar?

exergonic

Proton motive force

Energy generated by reductant in the form of NADH pushing electrons through the electron transport chain whilst oxygen pulls electrons out of the other end.

What does the proton motive force fuel

ATP synthase which makes ATP.

For each molecule of glucose, 10 NADH, and 2 FADH2...

The ETC converts this to around 38 molecules of ATP

What is the conversion of pyruvate to acetyl-CoA catalysed by

pyruvate dehydrogenase complex

pyruvate dehydrogenase complex

multi enzyme complex in the mitochondrial matrix

Terminal acceptor of electrons

Oxygen

Complexes in the ETC

Complex I, Complex II, Complex III, and complex IV

Free moving Electron acceptors in the ETC

Ubiquinone and cytochrome. They move fluidly within the membrane to transfer electron passengers between the electron chain complexes.

Reducing compounds

NADH (and FAD at Complex II). Push electrons into the chain whilst the electron acceptor oxygen "sucks" them out at the other end.

Why is it important that the complexes are bound to the inner mitochondrial membrane?

As they pump hydrogen ions from the matrix to the intermembrane space

What is the proton gradient generated between the matrix and intermembrane space used for?

To supply energy for ATP synthesis

How many protons needed to produce one ATP

4

Complex I AKA

NADH: ubiquinone oxidoreductase

What does Complex I do

NADH is oxidised by flavin mono-nucleotide. Electrons are transferred from four Fe-S centres to ubiquinone. Energy from this electron transfer is used to pump 4 protons across the intermembrane space

Complex I inhibitors

Rotenone, Nitric oxide. Both inhibit electron transfer from last FeS to UQ.

Complex II AKA

succinate ubiquinone oxidoreductase

What does complex II do?

The flavin protein oxidises succinate to fumarate whilst transferring 2 e- to FAD to make FADH2. Electrons are then transferred to the central proteins via the covalently bound Fe-S clusters

What would happen without complex II

No electrons would be transferred to complex III.

Complex II inhibitor

Malonate, malate, and oxaloacetate

Malonate

A competitive inhibitor. Inhibits electron transfer from last FeS to UQ

Complex III AKA

uniquinone cytochrome-c oxidoreductase

Two forms of Fe in Complex III

Haem iron, and iron in the Fe/S centre

What does Complex III do

Ubiquinol is oxidised at centre P whilst ubiquinone is reduced at centre N in a 2 step process. An electron is transferred to mobile cytochrome via a Rieske Fe-S centre and cytochrome c1. The second electron is then transferred to centre N via two b-type cytochromes. Two redox reactions drive the mitochondrial ETC.

Complex III inhibitors

Antimycin A - binds to N centre to block reduction of ubiquinone.

Complex IV AKA

Cytochrome C oxidase

What does complex IV do?

Accepts electrons from reduced cytochrome c on the outside of the inner membrane. Donates an electron to 1/2 O2 on the matrix side of the membrane. This combines with 2H+ to make water.

Complex IV inhibitors

Cyanide (acts on binuclear metal centre) , carbon monoxide (Competes with oxygen), Azide (binds to cytochrome C haem cofactor)

is oxidation endergonic or exergonic

exergonic

Why are reduction reactions endergonic?

non-spontaneous reactions that require extra energy to initiate the reaction.

redox potential

A measure of electron affinity

Electron affinity

The tendency of a molecule to acquire electrons and thereby be reduced.

NADH redox potential

Very negative (0.32 V) as its electrons are at a very high energy state and are easily pushed into the chain.

Proton Motive Force

The potential energy stored in the form of an electrochemical gradient, generated by the pumping of hydrogen ions across biological membranes during chemiosmosis.

ΔpH

chemical concentration difference (acidity) across the membrane

Δ y (psi) (actual symbol is unavailable)

Electrical potential (charge difference) across the membrane

Oligomycin

Antibiotic that inhibits the FO unit of ATP synthase

What does Fo bind to

oligomycin

adenine nucleotide and phosphate translocases purpose

Transport ADP and Pi back into the matrix to be made into ATP and newly synthesised ATP into the cytosol .

adenine nucleotide translocase

An antiporter - the same protein moves both ADP into the matrix and ATP out.

What does the proton motive force provide energy for

energy for ATP synthesis and transporting substrates (ADP and Pi) into and product (ATP) out of the mitochondrial matrix.

What is the terminal acceptor in anaerobic bacteria?

Nitrate, nitrite, Fe3+, sulfate, CO2, or small organic molecules such as fumarate.

What is the energy lost in dissipating the proton gradient used for

To generate heat

UCPs in thermogenesis

Such as in hibernation. Natural uncouplers are found in tissues such as adipose brown fat. Instead of making ATP, uncoupler protein called UCP1 is used to make heat.

The chemiosmotic hypothesis

Widely accepted as the mechanism of coupling electron transport and ATP synthesis

Evidence for the chemiosmotic model

pH inside the mitochondrion is approximately 1.4 units lower than outside. ATP is synthesised when a pH gradient is imposed on the mitochondria. An intact mitochondria is needed for ATP synthesis. Uncouples like DNP that carry protons across the inner membrane dissipate the proton gradient and stop ATP synthesis.

Equation to calculate PMF in coupled mitochondria

60 x pH on the outside of the mitochondrion x electrical potential

Iron-sulfur prosthetic groups

Each Fe-S centre covalently linked to cystiene and/or histidine residues within the protein.

Why are transition metals, like iron, useful in electron chains?

They can be reversibly oxidised and reduced so are great at passing electrons along the ETC.

Uses of Fe-S clusters

To stabilise proteins, substrate binding, Fe storage, donating sulfur groups during catalysis

What makes Complexes I, II and III metaloproteins?

they contain Fe-S clusters

What can flavin containing proteins be referred to as?

Flavoproteins or flavoenzymes

Ubiquinol

Reduced form of ubiquinone.

Plastoquinone

A lipid soluble co-enzyme. Shuttles electrons between photosystem II and the cytochrome b6f complex in PSI in the chloroplast thylakoid membrane.

Plastocyanin

Small water soluble copper-containing protein. Mediates electron transfer from PSII to cytochrome b6f complex and from PSI. Takes just one electron at a time.

Cytochrome c

Mobile electron carrier. Has heme prosthetic group. Ferries electrons from complex III to IV.