Oxidative phosphorylation

How much ATP is used by the body each day?

83 kg of ATP

How many times is ATP regenerated in a day?

300x a day

What is the redox potential of the oxidation of NADH and reduction of oxygen?

1.136 V

What is the free energy change during the oxidation of NADH and reduction of oxygen?

-219.21 KJ/mol, negative value shows a spontaneous reaction

What is the free energy required for the production of ATP?

+30.5 KJ/mol. Closer to 50 KJ/mol in cell conditions

What happens to the redox potentials between complexes in the ETC?

Values decrease, free energy becomes closer to 0 as energy is lost at each stage

What are the four complexes of the ETC?

NADH-coenzyme Q reductase
Succinate-coenzyme Q reductase.
Coenzyme Q-cytochrome c reductase.
Cytochrome c oxidase

What molecular components are present in the complexes in the ETC?

Flavoproteins, Coenzyme Q, Cytochromes, Fe-S proteins, protein bound Cu2+

What is the function of complex I?

Accepts 2e- from NADH

What is the function of complex II?

Entry point for FADH2

What is the function of complex III?

Oxidises reduced coenzyme Q, reduced cytochrome c

What is the function of complex IV?

Reduces molecular oxygen

What is the function of coenzyme Q?

Mobile electron carrier.
Highly hydrophobic, diffuses freely in the inner mitochondrial membrane

What is the function of cytochrome c?

Mobile electron carrier-Carries electrons to complex IV
Water soluble, associates along the membrane surface in its reduced state

What is the structure of complex I?

~900 kDa, >30 polypeptide chains.
1 FMN molecule, 7 Fe-S clusters

What is the first step of complex I action?

NADH binds to complex I on the matrix side of the inner mitochondrial membrane.
2e- from NADH transferred to FMN

What is the second step of complex I action?

2e- from FMNH2 transferred to a series of Fe-S centres

What is the third step of complex I action?

2e- from Fe-S centre transferred to coenzyme Q

What is the structure of complex II?

Contains succinate dehydrogenase.
~100-140 kDa.
FAD covalently bound to histidine residue in 68 kDa flavoprotein.
3 Fe-S clusters.
2 small subunits, with heme b

What is the first step of complex II action?

Succinate converted to fumarate, FAD reduced to FADH2

What is the second step of complex II action?

FADH2 transfers e- to an Fe-S centre, reduces coenzyme Q.

What is the structure of complex III?

Forms a dimer, each monomer has 11 proteins and is 248 kDa.
Fe-S Rieske protein.
3 cytochromes

What cytochromes are found in complex III?

b and c1. c is loosely associated

What occurs in complex III?

Q cycles

What occurs during the first half of the Q cycle?

One electron from coenzyme reduces cytochrome c, the other produces a semiquinone radical anion (Q-). 2H+ transported into the membrane space
Oxidised coenzyme Q returns to the Q pool

What occurs during the second half of the Q cycle?

Another reduced coenzyme Q molecule enters complex III.
One electron transferred to cytochrome c the other transferred to the radical anion.
2H+ transported into the membrane space

What occurs to the radical anion produced during the Q cycle?

Electron from coenzyme Q transferred to the radical, then 2H+ used to reduce the anion to coenzyme Q.

What is the structure of complex IV?

13 subunits, 204 kDa.
2 Cu centres which associate with cytochromes a and a3

What is the action of complex IV?

Pumps 4H+ into the intermembrane space.
4e- from cytochrome c and 4H+ from the mitochondrial matrix are used to produce water from O2

Which complexes transport H+ across the inner membrane?

Complex I, III, and IV

Why are no H+ transported from at complex II?

There is a small change in free energy, not large enough to transport protons across the membrane

How does the transport of H+ lead to the production of ATP?

Movement of H+ from the matrix increases pH and causes a negative charge in the matrix.
H+ can then move through ATP synthase channel down a charge and concentration gradient into the matrix

What is the structure of the ATP synthase channel?

Made of F1 and F0 subunits.
F1 contains α, β, γ, δ, and ε subunits.
F0 is a transmembrane protein and attached to F1, 3 hydrophobic subunits a, b, and c

Which side of the mitochondrial inner membrane is negative?

Matrix side

Which side of the mitochondrial inner membrane is positive?

Intermembrane space

What reactions must occur for the synthesis of ATP?

Translocation of H+, catalysis of ATP synthesis.

How does the translocation of H+ occur?

Carried out by F0, causes rotation of c complex and rotation of γ/ε stalk

How is ATP synthesis catalysed?

Conformational change of β subunits of F1, alters binding affinity for ATP/ADP, stabilised ATP

How is the H+ gradient dissipation coupled with ATP synthesis?

H+ through F0 drives γ/ε rotor. γ interactions with β subunit drive conformational change

How many H+ are required for the synthesis of ATP?

Movement of 3H+ through F0 required for 1 ATP, but 4H+ moved across per ATP synthesised

What is the function of the fourth H+ transported in ATP production?

Used as electrochemical energy devoted to mitochondrial ATP-ADP transport

What is the P/O ratio?

The number of ATP molecules generated for every electron pair

What is the P/O ratio for NADH?

10/4, 2.5

What is the P/O ratio for FADH?

6/4, 1.5

How can the ETC be regulated?

Substate availability, ADP/ATP levels, oxygen, proton motif force