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# Analysis of electron transport system

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Analysis of an electron transport system in the cell membranes of a previously
unknown Kingdom of organisms revealed that it contained the following components
with the redox half-reactions and standard reduction potentials shown in the Table.

Half-Reaction E'o(V)

Cytochrome R+ + e &#8594; Cytochrome R +0.35
Cytochrome T+ + e &#8594; Cytochrome T +0.20
Fp 73+ + e &#8594; Fp 73 -0.22
NO3- + 2H+ + 2e &#8594; NO2 - + H2O +0.42

how to Calculate &#916;Go' for the transfer of a pair of electrons between each of the
carriers in the electron transport system. use the

Nernst equation from this data determine :

i)the steps at which sufficient energy is released to transfer protons across the membrane, assuming &#916;Go' for proton transfer against its concentration gradient is 23 kJ per mole of protons.

ii. for one electron pair, the amount of potential energy in the proton gradient which is theoretically available for ATP synthesis under standard conditions. (pls show how you decided on this)

iii. the number of ATP molecules which could theoretically be synthesised per electron pair. (please show how u decided on this)

https://brainmass.com/biology/electron-flow/analysis-electron-transport-system-149226

## SOLUTION This solution is FREE courtesy of BrainMass!

I will show you how to do this and then you can finish it on your own. Sound fair? But don't worry, I'll guide you through the steps carefully.

Half-Reaction E'o(V)

Cytochrome R+ + e &#8594; Cytochrome R +0.35
Cytochrome T+ + e &#8594; Cytochrome T +0.20
Fp 73+ + e &#8594; Fp 73 -0.22
NO3- + 2H+ + 2e &#8594; NO2 - + H2O +0.42

First, we have to put these half-reactions in order. So, let's put them in order.

NO3- + 2H+ + 2e &#8594; NO2 - + H2O +0.42
Cytochrome R+ + e &#8594; Cytochrome R +0.35
Cytochrome T+ + e &#8594; Cytochrome T +0.20
Fp 73+ + e &#8594; Fp 73 -0.22

Second, now that they're in order, it's easy to know how the equation will flow. It will flow from NADH to fp73 to cytT to CytR to NO3-. In the end, H2O will be produced as the final reduced species. Remember, electrons flow from the half-reaction of lower standard reduction potential to the half-reaction of higher standard reduction potential.

Third, let's look at the first reaction. It is made up of the following two half-reactions:

Fp 73+ + e &#8594; Fp 73 -0.22

How will it work? We must reverse the direction of the half-reaction with the lowest reduction potential. When we do, we must reverse the sign of the reduction potential:

Fp 73+ + e &#8594; Fp 73 -0.22

Now, we need to create the entire redox reaction. However, notice that the half-reaction involving Fp73 is a one electron reaction while the one involving NADH is a two electron reaction. Therefore, we must double the reaction involving Fp73, BUT DON"T DOUBLE THE VOLTAGE VALUE!!!

2 Fp 73+ + 2e &#8594; 2 Fp 73 -0.22

Let's combine them now.

2 Fp 73+ + NADH &#8594; NAD+ + H+ + 2 Fp73

This is the first redox reaction that will take place. What is &#916;E'o? Just do the math. It is 0.100 V.

Fourth, we determine the free energy in this reaction.

&#916;G°' = -nF&#916;E'o

&#916;G°' = -2(96,480 J/V-mol)(0.100 V) = -19296 J/mol = -19.3 kJ/mol

That is the amount of free energy available in the first redox to transfer a "pair of electrons." This is important since we were asked to calculate &#916;G°' based on the flow of a pair of electrons. Is it enough to pump one mole of protons across the membrane? No, it is not. How do we know? We know because it requires 23 kJ/mol to move the protons whereas we only have -19.3 kJ/mol available. We don't have enough free energy available. The cost is too much and we can't pay for it.

Now, if you do the other reactions the same way, you should be fine. There should definitely be sufficient free energy to pump protons in the next reaction, the one involving Fp73 and CytT. After all, as you'll see the &#916;E'o = 0.420 V for that redox reaction and &#916;G°' for a pair of electrons is -81.0 kJ/mol.

Since we require 23 kJ/mol to pump protons, how much energy do we have left over? -81 + 23 = -58 kJ/mol.

Now we're left with the following two questions:

ii. for one electron pair, the amount of potential energy in the proton gradient which is theoretically available for ATP synthesis under standard conditions. (pls show how you decided on this)

We now have -58 kJ/mol of potential energy in the proton gradient theoretically available for ATP synthesis.

iii. the number of ATP molecules which could theoretically be synthesised per electron pair. (please show how u decided on this)

How much energy do we need to synthesize ATP? We need about 30.5 kJ/mol. Therefore, we have enough to make 1 ATP molecule at this point. -58 + 30.5 = -27.5 kJ/mol left over. We almost have enough for 2 ATP molecules at this point, but not quite.

(You now know how to do the rest yourself!)

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Thanks for using BrainMass, and have a great day.

Stephen Allen
OTA 104330

This content was COPIED from BrainMass.com - View the original, and get the already-completed solution here!