Dr. V. Siva Prabodh MD.

Professor

High energy phosphates & Low energy phosphates:

CompoundPhosphoenolpyruvate -14.8

Carbamoyl phosphate -12.3

1,3 – Bisphosphoglycerate -11.8

Creatine phosphate -10.3

ATP ADP + Pi -7.3

ADP AMP + Pi -6.6

Pyrophosphate -6.6

Glucose 1-phosphate -5.0

Fructose 6 –phosphate -3.8

AMP -3.4

Glucose 6 –phosphate -3.3

Glycerol 3-phosphate -2.2

Kcal/mol

-7.3ATP ADP +Pi

Adenosine Triphosphate (ATP)

Importance of Adenosine Triphosphate (ATP) ATP serves as the general "free energy

currency" for virtually all cellular processes.

It is a direct source of energy for cell motility, muscle contraction, and the specific transport of substances across membranes.

ATP is a source of phosphate energy for synthesis of the other nucleoside triphosphates via the reaction:

ATP is also an allosteric effector of many enzymes.

cytochromes: Protein-bound :- Heme containing carriers

Cytochromes constitute a family of colored proteins containing the Heme prosthetic group

Nature of e- Carriers: Protein-bound carriers :- Iron-sulphur centers

Fe ion is coordinated with the sulphurs of cysteine residues and inorgnic sulphur atoms.

Nature of e- Carriers: Mobile carriers :- Coenzyme Q

Coenzyme Q: small hydrophobic molecule and the only one that is not a part of protein.

Organization of carriers in ETC: Complex I

NADH dehydrogenase complex :

Largest Respiratory enzyme complex> 40 polypeptide chainsBound FMNAt least 7 iron-sulfur centersElectron transfer From NADH to Co QBlocked by Rotenone and Amytal

Complex IISuccinate Dehydrogenase :

It is a point of entry of electrons from FADH2 produced by the enzyme succinate dehydrogenase in the citric acid cycle.

FAD as Prosthetic group Iron-sulfur proteins Electron transfer From FADH2 to Co Q Thus, both complexes I and II donate their

electrons to the same acceptor, coenzyme Q.

Coenzyme Q : Benzoquinone linked to 10 isoprene units

It has the ability to accept electrons in pairs and pass them one at a time through a semiquinone intermediate to Complex III. This cycle is referred to as the Q cycle.

Electron transfer From Complex I or II to Complex III

Cytochrome c : This small mobile protein accepts

e- from Complex III and shuttles them to Complex IV

Complex III

Cytochrome b-c1 complex :

It is a Dimer Each monomer has: 3 Hemes bound to cytochromes 1 Iron-sulfur protein Electron transfer From Co Q to cytochrome c Cytochrome c then transfers e- to the

complex IV Blocked by Antimycin A

Complex IV

Cytochrome oxidase complex :

Dimer

Each monomer has: 13 Different polypeptide chains, including 2 Cytochromes a and a3 and 2 Cu atoms

Accepts one Electron at a time from Cytochrome c and passes them four at a time to Oxygen

Blocked by Cyanide, Azide, and Carbon monoxide

Organization of carriers in ETC:

Oxidative Phosphorylation Chemical coupling

Chemiosmotic hypothesis

- proposed by Mitchel

- dependent on proton gradient.

Chemiosmotic Coupling:

1. The active transport of electrons pumps protons out of the mitochondrial matrix into the inter membrane space.

2. An electrochemical gradient of protons is created, outside the inner mitochondrial membrane than inside.

The protons on the outside have a thermodynamic tendency to flow back in.

3. When protons do flow back into the matrix, the free energy arising from the gradient (21 kJ/mol of protons) is dissipated, with some of it being used to drive the ATP synthesis.

Chemiosmotic Coupling

ATP Synthase:

ATP synthase or F0F1 complex or

Complex V

Head F1

Stalk F0

P:O Ratio

The P:O ratio refers to: the number of Inorganic Phosphate

molecules utilized for ATP generation for every atom of Oxygen (a pair of e-) consumed.

.

P:O Ratio

Electrons entering the system at complex I from

NADH have a P/O ratio of about 3/1.

Electrons entering the system at complex II FADH2's have a P/O ratio of about 2/1.

ATP Synthesis by ATP Synthase

Boyer’s Binding Change Mechanism

Inhibitors of ETC

Inhibitors of ETC: Bind to one of the components of ETC and Block

the transport of Electrons.

At Complex I: Rotenone, Amytal & Piericidin A Between cyt b and c1: Antimycin A & BAL At Complex IV: CO, Cyanide, Azide & H2S

Inhibitors of Oxidative Phosphorylation:

Uncouplers: 2,4- DNP, FCCP (trifluoro carbonyl cyanide phenyl hydrazone)

Thyroxin, FFABlocks between oxidation and

phosphorylation

Ionophores: Valinomycin, Nigercin alters the permeability of mitochondrial

membrane

Other Inhibitors

Oligomycin: ATP synthase Atracyloside: Adenine nucleotide

carrier(Translocase)

Thank you