BIOENERGETICS - SRM Institute of Science and Technology · BIOENERGETICS. FREE ENERGY. ... free...

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BIOENERGETICS

Transcript of BIOENERGETICS - SRM Institute of Science and Technology · BIOENERGETICS. FREE ENERGY. ... free...

BIOENERGETICS

FREE ENERGY

It is the portion of the total energy change in a system that is available for doing work at constant temperature and pressure; it is represented as ΔG.Reactions involving free energy:

1. Exergonic2. Endergonic

EXERGONIC REACTIONS

Reactions in which the free energy of the final state is less than the free energy of the initial state.This represents energy that can be used to do biological workReaction is spontaneous or favorable.ΔG is - or <0

ENDERGONIC REACTIONSReactions in which the free energy of the initial state is less than the free energy of the final state.ΔG is + or >0Reaction is nonspontaneous or unfavorableConsiderable amount of energy must be imparted to the system

COUPLED REACTIONS: 2 TYPES

1. Coupling involves a common obligatory intermediate (I)A+C I B+D

2. Synthesizing a compound of high-energy potential in the exergonic reaction and incorporate this new compound into endergonic reaction.

AH2

A Carrier-H2

Carrier

B

BH2

The overall free energy change for the reaction is negative (ΔG < 0)

HIGH ENERGY PHOSPHATES

High energy phosphates play central role in energy capture & transfer.

E

1

2

3

4

EXERGONIC

SYNTHESIS

MUSCULAR CONTRACTION

NERVOUS EXCITATION

ACTIVE TRANSPORT

HIGH ENERGY COMPOUNDSCompound ΔG (Kcal/mol)

Phosphoenolpyruvate -14.81,3 bisphosphoglycerate -11.8Phosphocreatine -10.3ATP( ADP+Pi) -7.3AMP(Adenosine+Pi) -3.4PPi( 2Pi) -4.0Glucose-1-phosphate -5.0Fructose-6-phosphate -3.8Glucose-6-phosphate -3.3

ENERGY CURRENCY OF CELL

High energy phosphates act as energy currency of cell.3 major sources of high energy phosphates takingpart in energy conservation or energy capture.

1. Oxidative phosphorylation: Free energy to drive this process comes from Respiratory chain oxidation using molecular O2 in mitochondria.

2. Glycolysis:

3. TCA Cycle:

ROLE OF ATP/ADP CYCLE IN TRANSFER OF HIGH ENERGY

PHOSPHATES

P CREATINE- P

CREATINE

store of P

SUCCINYL Co-A

PEP1,3 BPG

OXIDATIVE PHOSPHORYLATION

ATP

ADP

P

Gl 1,6 BPG6PGlycerol3P

OtherPhosphorylations

BIOLOGICAL OXIDATION

BIOMEDICAL IMPORTANCE

Respiration

Xenobiotics (metabolism by Cytochrome P450 system).

Hyperbaric oxygen therapy in patients with respiratory or circular failure.

May result oxygen toxicity.

ENZYMES INVOLVED IN OXIDATION & REDUCTION:

OXIDOREDUCTASES

Oxidases Dehydrogenases Hydroperoxidases Oxygenases

OXIDASESCatalyse the removal of hydrogen from

a subtrate using oxygen as a hydrogen acceptor.

A

AH2

AH2

A

1/2 O2

H2O2

H2O

O2

e.g.1. Cyt. Oxidase

2. L-AA oxidase

3. Xanthine oxidase

4. Glucose oxidase

DEHYDROGENASESTransfer of hydrogen from one substrate to another in a

coupled oxidation - reduction reaction. Can’t use O2 as H2acceptor.

AH2

A Carrier -H2

Carrier BH2

B

Depend on:

1. Nicotinamide coenzymes2. Flavin coenzymes3. Cytochromes

HYDROPEROXIDASES

Use H2O2 or organic peroxides as substrates.

2 types:

1. Peroxidases

2. Catalases

O22H2O2

H2O2 AAH2+

2H2O

2H2O

+

+Peroxidases

Catalases

Glutathione peroxidase2GSH + 2H2O+ GSSGH2O2

OXYGENASES

Catalyze direct incorporation of oxygen into a substrate. Takes place in 2 steps:

1. O2 binding to the enzyme at active site, &

2. The reaction in which bound O2 is reduced/transferred to substrate.

2 subgroup of oxygenases:

i. Dioxygenases

ii. Monooxygenases

Dioxygenases: Incorporate both atoms of molecular oxygen into the substrate.

A+O2→AO2

e.g.i. Homogentisate oxidaseii. L-tryptophan dioxygenaseiii. 3-hydroxyanthranilate dioxygenase

Monooxygenases: Incorporate only one atom of molecular oxygen into the substrate.

May be Microsomal or Mitochondrial.A-H + O2 + ZH2 →A-OH + H2O + Z

DRUG-H + O2 + 2Fe2+ + 2H+ →DRUG-OH + H2O + 2Fe3+

Hydroxylase

RESPIRATORY CHAIN & OXIDATIVE PHOSPHORYLATION

Respiratory chain oxidizes reducing equivalents and acts as a proton pump.Oxidative phosphorylation is the process by which liberated free energy is trapped as high-energy phosphate.

ELECTRON TRANSPORT CHAIN

4 sequential complexes found in the inner side of inner mitochondrial membrane.

They accept e- from e- donors such as NADH or succinate, shuttle these e- across the membrane creating an electrical & chemical gradient (+1.1V).

Through the proton driven chemistry of the ATP synthase, generate ATP.

Complex I -NADH dehydrogenase/ NADH Coenzyme Q reductase.

Fp Q

Complex II- Succinate -Coenzyme Q reductase

Complex III -Coenzyme Q -cytochrome c oxidoreductase

Cyt-C

Complex IV -Cytochrome c oxidase.

½ O2 + H+

H2O

COMPLEXES OF ETC

ETC COMPONENTSComplex Components Prosthetic group

I NADH-Q oxidoreductase FMNFe-S

II Succinate Q reductase FADFe-S

III Q-Cytochrome C oxidoreductase

Heme bHHeme bLHeme C1

Fe-s

IV Cytochrome c oxidaseHeme aHeme a3

CuA & CuBATP synthase

H+

H+ H+H+H+

H+H+H+

H+ H+

H+H+

H+H+ H+

H+H+

H+ H+

ATP

Oxidative phosphorylation- Two phases

2. Using the gradient's energy to make ATP

1. Generation of the proton gradient.

TRANSPORT OF REDUCING EQUIVALENTS THROUGH ETC

AH2

A

NAD+

NADH Fp

FpH2 2Fe3+

2Fe2+

H2O

½ O2

H+ 2H+2H+H+

QFp [FMN] FeS

Fp [FAD] FeS

Succinate Choline

NADFp [FAD]

Lipoate

Pyruvate

α - Ketoglutarate

Fp [FAD]

FeS ETF [FAD]

Fp [FAD] FeS

Glycerol 3 phosphate

Acyl - CoASarcosine

Dimethylglycine

Proline3- Hydroxyacyl - CoA

3- HydroxybutyrateGlutamate

MalateIsocitrate

I

II

Q Cyt bFeS

Cyt c1 Cyt c Cyt aa3

CuO2

III IV

Q CYCLE

CYTOSOL(OUTSIDE)

MATRIX(INSIDE)

INNER MITOCHONDRIAL MEMBRANE

QH

QH

C1

QH2 H+H+

Q

H+

e-

e-

H+

e-

b566

b562

ATP Synthase

F1 subunit has 5 types ofpolypeptide chains(α3, β3, γ, δ, ε)

F0 contains the proton channelring of 10-14 c subunits

Moving unit (rotor) is c ring & γεRemainder is stationary (stator)‘a’ subunit binds

to outside of ring

Exterior columnhas 1’ a’ subunit2’ b’ subunits, &the δ subunit

Subunit a

Proton enters

Proton exits

The Binding Change Mechanism (Paul Boyer)

P:O RATIO

When substrates oxidized by NAD-dehydrogenase, 3 mol ATP is produced per ½ mol of O2 consumed. P:O= 3.

When substrates oxidized by AFD-dehydrogenase, 2 mol ATP is produced per ½ mol of O2 consumed. P:O= 2.

INHIBITORS OF ETC

FMN,FeS Cyt b, FeS, Cyt c1Cyt a Cyt a3Cu Cu

Q Cyt c

FADFeS

Complex IV

Complex III

Complex II

Complex I

Succinate

ADP + Pi ADP + PiADP + PiATPATPATP

O

H2O

NADH

Uncouplers

Oligomycin

Malonate

BALAntimycin A

CN, COAzide, H2S

Piericidine Amobarbital Rotenone

Carboxin TTFA

CHEMIOSMOTIC THEORY (Mitchell)

ATP synthase

ADP+Pi ATP

H+

OLIGOMYCIN

H+

H+

H+

H+

H+

H+

I

Q

III

C

IV

Proton translocation

NADH+H+

NAD+

1/2O2

H2OUncouplers

InnerMitochondrial

membrane

_

+

Transport of Reducing Equivalents

SHUTTLE PATHWAYS

SHUTTLE PATHWAYS

Two pathways:1. Glycerol Phosphate Shuttle - Muscle & Brain2. Malate-Aspartate Shuttle - Liver, kidney &

heart

They transport the reducing equivalents from cytosol to mitochondria and not vice versa.

Malate aspartate shuttle

Malate Malate

Oxaloacetate

NAD+

NADHH+

Cytosol Mitochondria

+Oxaloacetate

NAD+

NADH+ H+α - KGα - KG

1

Glutamate GlutamateAsp Asp

2

H+ H+

Malate dehydrogenaseMalate dehydrogenase

TransaminaseTransaminase

Liver, kidney & heart

Glycerol 3 phosphate

NADH

H++

Glycerol 3 phosphate

Dihydroxy acetone phosphate

Dihydroxy acetone phosphate

FADH2

FAD

Glycerol 3 PO4 dehydrogenase

Glycerol 3 PO4 dehydrogenase

Cytosol Mitochondria

Resp. chain

Glycerophosphate shuttle

NAD+

Muscle & brain

TRANSPORTER SYSTEMS

1 2 543 6

OUTSIDE

INSIDE

OH-

H2PO4

Pyruvate

H+

HPO4-2

Malate-2

Malate-2

Citrate-3+H+

Malate-2

α-KG-2

ADP3-

ATP4-

1. Phosphate 2. Pyruvate 3. Dicarboxylate 4. Tricarboxylate 5. α-KG 6. Adenine nucleotide

N-Ethylmaleimide

Atractiloside