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How is the energy of Oxidation Preserved for the synthesis of ATP?. ANS: Electron transfer to oxygen is accompanied by the formation of a high energy proton gradient. The Gradient arises by having protons pumped from the matrix side of the mitochondria to

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How is the energy of Oxidation Preserved

for the synthesis of ATP?

ANS: Electron transfer to oxygen is accompanied

by the formation of a high energy proton gradient.

The Gradient arises by having protons pumped

from the matrix side of the mitochondria to

the inner membrane spaces

Back flow of the protons to the matrix leads

to the synthesis of ATP.


H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

O2

O2

O2

O2

O2

O2

O2

Cyt C

H2O

H2O

H2O

H2O

H2O

H2O

H2O

H+

Inner

membrane

space

H+

H+

H+

H+

H+

H+

I

III

IV

NADH

II

H+

H+

H+

H+

H+

Matrix

side

PROTON GRADIENT FORMATION

(The Chemiosmotic Model of Energy Conservation


The Q-Cycle (Complex III-Cytbc1 complex)

One electron goes on to Cytoc1, the other stays in the Q cycle

Text p700


2 protons come from QH2

2 protons come from matrix

QH2 + 2 cytc1 (oxidized) + 2H+N (matrix side)

Q + 2 cytc1 (reduced) + 4H+P (inner membrane)


4. Given A. The chemical potential of A is said to be GA or

the partial molar free energy of A.

GA - Go’A = RTln[A]

Free Energy Considerations (Chapt 11, p 398)

1. All substances in solution have a chemical potential

2. The chemical potential is related to concentration

3. Chemical potential is related to free energy

5. In terms of free energy of A:

This equation says the free energy of A

depends on the concentration of A


Equation assumes

A goes from out to in

GA = GA(in) - GA (out)

[A]out

[A]in

= RT ln

= RT ln

[A]in

[A]out

[A]in

- RT ln

=

[A]out

A across a membrane

1. A difference in the concentration of A across a

membrane creates a chemical potential difference

2. The difference is the difference of the chemical potential

on either side:

3. A in to out:


[A]in

[A]out

[A]in

DGA = RT ln

DGA = RT ln

[A]in

[A]out

[A]out

Proton Gradient Energy

How much energy must be expended to transfer

a proton from the matrix to the inner membrane?

A

outside

A A A A A A

A A A A A A

inside

A A A

A A A

A

= RT ln

Since [A]in < [A]out

Since [A]in < [A]out

DGA = negative

DGA = positive

Spontaneous

Endergonic Requires ATP


Electrochemical

potential

DGH+ = 2.3RT DpH

+ ZFDY

[H+]out

[A]in

DGA = RT ln

[A]out

[H+]in

DGH+ = RT ln

+ ZFDY

DGH+ = 2.3RT log

[H+]out -

log[H+]in

+ ZFDY

DGH+ = 2.3RT [pH (in)

– pH (out)] + ZFDY

Proton Gradient Energy

The CHEMIOSMOTICPrinciple

If A is ionic (has a charge)

A+

Read Chapter 19

p703

outside

+ + + + + +

Dy

inside

– – – – –

Z = charge on ion

H+

F = Faraday’s constant

+ ZFDY


= 5.70 kJ/mol x DpH + (1) 96.5 kJ/mol-volt x DY

volts

DGA = 2.3RT DpH

+ ZFDY

Problem: Calculate the pmf of a mitochondrial membrane

that has a membrane potential of 168 mV and whose matrix

pH is 0.75 units higher than its intramembrane space.

= 5.70 x (.75) + 96.5 x .168

= 4.12 kJ/mol + 16.21 kJ/mol

pH gradient (20%)

Membrane potential (80%)

= 20.45 kJ/mol of protons

The pH gradient and the Membrane potential

both contribute to the proton motive force.


ADP + Pi ATP + H2O

F1 = stalk and lollypop

Fo = base

How is ATP made?

DG = + 30.5 kJ/mol

FoF1 ATPase Complex (ATP Synthase)

1. An ATP making machine

2. Driven by a proton gradient

3. Attached to the inner mitochondria membrane


3 non-equivalent sites

H+

Matrix

F1

FO

Intermembrane space

FOF1 ATPase (ATP Synthase)

Binding-Change Model


Loose Site

Tight Site

ATP

ab

(ADP and Pi bind)

ADP + Pi

F1

Open Site

(ATP is released)

(ATP is formed and

held)

ATP

ab

ab

3-Site Model of ATP Synthesis

The flow of protons through F1 makes the sites

alternate much like a spinning propeller.


Site 1

Site 2

Site 3

ADP + Pi

ATP

ADP + Pi

ATP

ADP + Pi

ATP

Older Model of ATP Synthesis

FADH2

NADH FMN CoQ Cyt b Cyt c1 Cyt c Cyt a+a3 O2

Model was tested by measuring P/O ratios


NADH

~3

~2

FADH2

~2

Succinate

P/O Ratios

What is it?

P is phosphate taken up (incorporated into ATP)

O is the oxygen taken up (measured as atomic oxygen)

(Equated to a pair of electrons traveling to O2)

What is the significance?

Compares substrate efficacy to form ATP

Examples:

P/O

Assumed to be whole intergers based on the “coupling site” model of ATP synthesis


Chemiosmotic adjustment to p o
Chemiosmotic Adjustment to P/O

  • 10 protons are pumped for each electron pair from NADH

  • 6 protons are pumped for each electron pair from FADH2

  • 4 protons are required to make one ATP

  • 1 of the 4 is used in transport of ADP, Pi and ATP across mitochondrial membrane

  • Therefore, 10/4 or 2.5 is the P/O ratio for NADH

  • Therefore, 6/4 or 1.5 is the P/O ratio for FADH2


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