Metabolism 2 - Oxidative phosphorylation

What is a substrate level phosphorylation reaction (SLP)

It couples a really exothermic reaction with the phosphorylation of ADP → ATP

Examples of SLP

• in Glycolysis - convert 3 - bisphophate glycerotae into 3-phosphaglycerate (1 Pi lost used to amke ATP)

• Cotric acid cycle breaking bond between succinil and CoA enzyme realease engy to make GTP (or ATP)

where does most of out ATP form cells come from

oxidative phosphorylation

What happens in oxidative phosphorylation

reduced Co-enzymes like NADH and FADH2 become oxidized by passing on their hydrogen and this is coupled with synthesis of ATP

Structure of mitrochondria

• Outer membrane → highly permeable, large protein channels , high [H+] so low pH in inter membrane space and in cystol

• Inner membrane → highly impermeable, highly folded, selective what it lets through, less [H+] in matrix so high pH

Source of reduced Coenzymes?

• get it through oxidation of fatty acid, amino acids as well as in citric acid cycle get reduced Coenzymes

• Glycolysis formed NADH but happens in cystol

• use Maltate - Aspartate shuttle to get it through to be used in matrix

How does teh Maltate -Aspartate shuttle work

• what happens in in the cytosol oxalacetate is reduced to make Maltate

• Maltate can move into mitrchondria as has a channel for it

• once in matrix maltate is oxidized to make oxolactate again and forming reduced NADH in the matrix

• Oxolactete moves out and whole things starts again

• so we use NADH outside of cell to make NADH inside

• both reactiosn done by Maltate dehydrogenase

  

What are the parts of OP

2 parts:

• Oxidation → done by ETC (using complexes 1-4)

• Phosphorylation

What happens at Complex 1

• Complex 1 is an enzyme that catalyses the process of :

• NADH oxidation

• Transfers 2 electrons to Co-enzyme Q so this Co enzyme is reduced (small dissolved molecule found in inner mitochondrial membrane)

What happens at complex 3

• Catalyses the transfer of electrons form Co-Enzyme Q to cytochrome C

• Cytochrome C is a small molecule that is loosely attached to outside of inner membrane

What happens at complex 4

• Enzyme that catalyses the transfer of electrons form cytochome C to oxygen

• makes ½ oxygen - need 4 electrons to make full Oxygen

• Oxygen gets transferred to water

What is the energy used taht is realeased by ETC raections

• ETCR are very exothermic

• this energy released is used to pump H + out of matrix (which has a positive Gibbs free energy)

• complexes constantly pumping H+ out leading to high pH in matrix

  

If a compound rather be reduced it has…

• a positive reductive potential

• a negative Gibbs free energy

If a compound rather be oxidized it has….

• relatively negative reduction potential

• has a positive Gibbs free energy

Whihc reaction goes in forward and backward direction

• positive reduction potential → forward direction

• Negative reduction potential → backward direction

how to work out change in reduction potential

more positive reduction potential - more negative reduction potential (answer in V)

The higher the difference in reduction potential..

the more energy is released by transfer

How do we work out how much energy is realeased

Electron carrieres

• found in complexes and help them carry out redox reactions

Examples of these protein carriers

• Iron sulfur protein → has iron, sulfur and cysteine residues, take part in 1 electron transfer

• Cytochorme → has heam group contently boned together, iron ion in center, takes part in directly 1 electron transfer

• Flavin mononuclotide → looks like FAD can tarnsfer or hold 2 hydrogen’s

• Ubiquonone→ can transfer electrons through hydrogen

how many protons get pummped out from 1 NADH

10 protons

What are these protons used for

• ATP synthase uses this proton gradient (high concentration of protons outside then inside ) and the charge element (more positive charge on outside then inside) a 2 reasons why its favorable for protons to enter

• ATP synthase uses this gradient to make ATP

What does Beta subunit do

• hold together ADP and Pi to be converted into ATP

• there are 3 of them and blue ones hold them together

Gamma and C subunits

• Gamma sub-unit interact with B sub-unit

• Gamma stalk can turn to help change shape of beta sub-unit to bind to ADP and Pi

• Gamma is able to turn because of C sub-unit turning

Why are C sub-units turning ?

• In C sub unit have an aspartate residue where protons can bind

• When have proton bound 0 no change , no protein -1 charge

• when charge is 0 easy of it to turn

• A sub-unit has 2 half channels for protein one to go into matrix and one for protons to wait before

Beta subunit conformtaion

• Open → can bind ADP and Pi and can loose them

• Loose → binds ADP and Pi but cannot loose them

• Tight → can only bind ATP

  • every time gamma stalk turns causes change in beta sub-unit conformation

    

calculate P:O ratio for NADH with ATP synthase with 8 sub-units

If ETC is not working the..

ATP synthase is also not working

• have coupling of the 2 processes