M.Prasad NaiduMSc Medical Biochemistry,Ph.D.Research Scholar

Bio-energitics is the study of energy changes [ release or utilization ] in biochemical reactions.

Reactions where energy is released are called exergonic reactions.

Reactions where energy is utilized are

called endergonic reactions.

Free energy [G] Gibb's change in free energy [ G] negative positive zero Standard free energy [ Go] Enthalpy [ H] Entropy [ S]

Free energy [G] denotes the fraction total energy in the system available to do the work .

Gibbs change in free energy [ G] It is the portion of free energy that is useful to do the work.

Standard free energy change [ G0 ] is

the free energy change under standard conditions [ pH 7 and 1M\ L concentration]

Gibbs Change in free energyGibbs Change in free energy [ [ G G ]] predicts whether a reaction is favorable or not predicts whether a reaction is favorable or not and the energy available to do work. and the energy available to do work.

1. exergonic reactions ; negative 1. exergonic reactions ; negative 2.endergonic reactions ; positive 2.endergonic reactions ; positive 3.equilibrium reactions ; zero 3.equilibrium reactions ; zero

Enthalpy [H]Enthalpy [H] is the measure of the change in the is the measure of the change in the heat content of the system i.e. energy released or heat content of the system i.e. energy released or absorbed. absorbed.

Entropy [S]Entropy [S] It is the fraction of enthalpy that is not It is the fraction of enthalpy that is not available to do the work. it denotes the randomness of available to do the work. it denotes the randomness of the products and reactants.the products and reactants.

A biochemical reaction depends on the change in free energy , Enthalpy , and Entropy.

G = H - T S [T= absolute temperature in Kelvin]

ATP is the energy currency of the cell ATP on hydrolysis yields -7.3 Kcal

ATP ADP + Pi - 7.3 Kcal

ATP is utilized for Active transport Nerve conduction Muscle contraction synthetic reactions

1.Pyro-phosphates -------------- ATP 2.Acyl phosphates -------------- 1,3-BPG 3.Enol phosphates -------------- PEP 4.phosphoguanides ------------- creatine –P 5.Thio - esters ------------- Acyl-co A the high energy bond in these compounds is called as

Acid –anhydride bond

phopho enol pyruvate [-14.8Kcal] phospho creatine 1,3-BPG SAM ATP - 7.3Kcal ADP G-1-P F-6-P G-6-P [-3.3Kcal]

The electrons flow uni directionally from one carrier to the other in ETC.

The carriers are reduced when they accept the electrons and get oxidized when they donate to the other carrier.

the reduced and oxidized forms of the same carrier are referred as redox pairs.

Redox potential is the tendency of the redox pair to donate or accept electrons.

electrons always flow from negative to positive redox potential.

REDOX PAIRS REDOX POTENTIAL

1. NADH\NAD -0.32 2. FADH\FAD -0.12 3. H2O\O2 +0.82

The ETC is arranged in the increasing order of their redox potentials.

All the enzymes of biological oxidation belongs to the major class of oxido-reductases. They are classified as follows 1.Oxidases 2.Oxygenases 3.Hydroperoxidases 4.dehydrogenases

Class Oxido reductases:

1. Oxidases Eg: Cytochrome oxidase

2. Oxygenases

Mono-oxygenases Eg: Cyt P450

Dioxygenases Eg: Tryptophan dioxygenases

3. Hydroperoxidases

Peroxidases Eg: Glutathione peroxidase

Catalases

4. Dehydrogenases

Aerobic Eg: Xanthine oxidase

Anaerobic:

a. NAD linked

b. FAD linked

c. FMN linked

1.Oxidases ; these enzymes catalyze the removal of hydrogen from the substrates.

Oxygen acts as acceptor of hydrogen forming water.

E.g. cytochrome -oxidase ,MAO A H2 +1\2 O2 ---------- A + H2O

2.Oxygenases 1. Mono-oxygenases [ mixed function oxidase] incorporates one oxygen atom into the substrate other is reduced to water. E.g. cyt-P450 ,tyrosine hydroxylase etc.

A-H + O2 + BH2 AOH + H2O +B

2. di-oxygenases incorporate both oxygen atoms into the substrate.

E.g. Tryptophan dioxygenase A H + O2 AOOH

3. Hydroperoxidases act on H2O2.

1. peroxidase ; glutathione peroxidase AH2 +H2O2 ---------2H2O + A

2.catalase; 2H2O2 ----------------2H2O +O2

4.Dehydrogenases Catalyze the removal of hydrogen from the

substrate. Based on the type of H2 acceptor they are

classified as follows

1. aerobic dehydrogenases oxygen is the acceptor of hydrogen.

2. anaerobic dehydrogenases coenzymes act as acceptors of hydrogen NAD+ linked dehydrogenases

NADP+ linked dehydrogenases FAD- linked dehydrogenases

Aerobic dehydrogenases These are flavoproteins and the product formed is

mostly hydrogen peroxide AH2 + O2 -------------A + H2O2

E.g. xanthine oxidase, glucose oxidase etc

Anaerobic dehydrogenases hydrogen acceptor s are co-enzymes. When the substrate is oxidized the co-enzyme is reduced

AH2 + B ----------------A + BH2

Transport of electrons from reduced substrates to O2 is called as ETC.

Site: Inner mitochondrial membrane Components: 1.Nicotinamide nucleotides [NADH + H+ / NAD+] 2.Flavo-proteins [FADH2 / FAD+].

3.Ubiquinone: CoQ. 4. Cytochromes: b, c1, c, a, a3.

ETC components are arranged in four

complexes in the increasing order of

their redox potentials from -4.2 for

(NADH + H+) to +0.82 for O2.

Complex I: NADH + H+----- CoQ reductase.

II: Succinate ----- CoQ reductase.

III: Co-Q ------- Cyt C reductase.

IV: Cytochrome oxidase.

ATPsynthase[ v ]

ATP synthase – Complex 5

Integral protein in the inner mitochondrial membrane.

It has two units F0 & F1. F0 acts as a protein channel. F1 has ATP synthase activity.

1.Nicotinamide nucleotides [NADH + H+ and NAD+] 2. flavo-proteins [ FADH2 and FAD+ ]

3. Co- Q [ubiquinone]

4. cytochromes

P;O ratio is the number of P atoms utilized To synthesize ATP for one atom of O2 oxidized

P;O ratio for NADH + H+ is ‘3’ [three sites of ATP synthesis]

P;O ratio for FADH2 is ‘2’ [two sites of ATP synthesis]

1. Chemical coupling: Generation of ATP at substrate level.2. Conformational coupling: Conformational changes in the molecules

in mitochondrial membrane leads to ATP generation.3. Chemi -osmotic theory: The proton

gradient generated during electron transfer is utilized for ATP synthesis.

Site specific:

1. NADH + H+ to CoQ; 1.Rotenone 2.piericidin 3. amylobarbital

2. Cyt b to Cyt c1

1. Antimycin 2. BAL. 3. Cyt a3

to O2 1. HCN 2. H2S 3. CO.

Uncouplers: 2,3 dinitrophenol, 2,3 dinitrocresol Physiological uncouplers: Large doses of 1. Unconjugated bilirubin, 2. Thyroxine 3. Aspirin 4. Long chain fatty

acids.

1. Oligomycin : Blocks ATP synthase activity. 2.Atractyloside : Block the proton flow into the

mitochondrial matrix.