How is the energy of Oxidation Preserved for the synthesis of ATP?

ANS: Electron transfer to oxygen is accompaniedby the formation of a high energy proton gradient.

The Gradient arises by having protons pumpedfrom 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+

H+

H+

H+

H+

H+ H+

H+

H+

H+

H+

H+H+

III

III IVNADHCyt C

O2

H2O

O2

H2O

O2

H2O

O2

H2O

O2

H2O

O2

H2O

O2

H2O

PROTON GRADIENT FORMATION(The Chemiosmotic Model of Energy Conservation

Inner membrane space

Matrix side

In this simplistic rep

QH2 QH2 Matrix SideCytosolic Side

Q-.

Fe-S

2 H+

Cyt c1

Cyt b566

Cyt b562

Q Q

Q-.2 H+

The Q-Cycle (Complex III-Cytbc1 complex)

Text p700Text p700

One electron goes on to Cytoc1, the

other stays in the Q cycle

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

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

2 protons come from QH2

2 protons come from matrix

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:

GA - Go’A = RTln[A]

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

the partial molar free energy of A.

This equation says the free energy of A depends on the concentration of A

This equation says the free energy of A depends on the concentration of A

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:

GA = GA(in) - GA (out)

= RT ln [A]out

[A]in

3. A in to out:

Equation assumes

A goes from out to in

Equation assumes

A goes from out to in

- RT ln [A]in

[A]out

=

= RT ln [A]in

[A]out

Proton Gradient Energy

How much energy must be expended to transfer a proton from the matrix to the inner membrane?

A A A A A A

A A A

outside

inside A

GA = RT ln [A]in

[A]out

Since [A]in < [A]out

GA = negative

Spontaneous

A A A A A A

A A A

A

GA = RT ln [A]in

[A]out

GA = positive

Endergonic Requires ATP

Since [A]in < [A]out

= RT ln [A]out

[A]in

Proton Gradient Energy

A+

– – – – –

outside

inside

GA = RT ln [A]in

[A]out

+ + + + + +

Z = charge on ionF = Faraday’s constant

+ ZFGH+ = RT ln[H+]out

[H+]in

+ ZF

GH+ = 2.3RT [pH (in) – pH (out)] + ZF

GH+ = 2.3RT log [H+]out - log[H+]in + ZF

H+

GH+ = 2.3RT pH + ZF

The CHEMIOSMOTIC Principle

Read Chapter 19p703 Electrochemical

potential

If A is ionic (has a charge)

Problem: Calculate the pmf of a mitochondrial membranethat has a membrane potential of 168 mV and whose matrix pH is 0.75 units higher than its intramembrane space.

= 4.12 kJ/mol + 16.21 kJ/mol

pH gradient (20%) Membrane potential (80%)

= 20.45 kJ/mol of protons

GA = 2.3RT pH + ZF

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

= 5.70 kJ/mol x pH + (1) 96.5 kJ/mol-volt x volts

The pH gradient and the Membrane potentialboth contribute to the proton motive force.

The pH gradient and the Membrane potentialboth contribute to the proton motive force.

How is ATP made?

G = + 30.5 kJ/molADP + Pi ATP + H2O

FoF1 ATPase Complex (ATP Synthase)

1. An ATP making machine

2. Driven by a proton gradient

3. Attached to the inner mitochondria membrane

F1 = stalk and lollypop

Fo = base

F1

FO

FOF1 ATPase (ATP Synthase)

Matrix

Intermembrane space

H+

Binding-Change Model

3 non-equivalent sites

ADP + Pi

ATP

ATP

3-Site Model of ATP Synthesis

Loose Site

(ADP and Pi bind)

Tight Site

(ATP is formed and held)

Open Site(ATP is released)

The flow of protons through F1 makes the sites alternate much like a spinning propeller.

F1

Older Model of ATP Synthesis

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

ADP + Pi ATP

Site 1

ADP + Pi ATP

Site 2

ADP + Pi ATP

Site 3

FADH2

Model was tested by measuring P/O ratios

P/O Ratios

P is phosphate taken up (incorporated into ATP)

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

What is it?

What is the significance?

Compares substrate efficacy to form ATP

Examples: P/O

NADH ~3

FADH2~2

Succinate ~2

Assumed to be whole intergers based on the “coupling site”

model of ATP synthesis

(Equated to a pair of electrons traveling to O2)

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