oxidative phosphorylation by dr. ashok kumar j

OXIDATIVE PHOSPHORYLATION

Dr. Ashok Kumar JInternational Medical School

Management and Science UniversityMalaysia

Dr. Ashok Kumar J; Professor; Biochemistry

Oxidation is defined as the removal of electrons

Reduction as the gain of electrons

Oxidation is always accompanied by reduction of an electron acceptor

Fe2+ Fe3+

e- (Electron)

Cu+ Cu2+

e- (Electron)

Fe2+ + Cu2+ Fe3+ + Cu+


Entire process is known as cell respiration

OXIDATION OF METABOLIC FUELS IS ESSENTIAL TO LIFE

Higher organisms dietary fuels are metabolized to:1. Carbon dioxide (CO2 ; Fully oxidized form of carbon) 2. Water fully reduced form of oxygen

Fuels

Oxidized

Electrons are transferred to

coenzymesETC

ATPADP

CO2

½ O2

H2O


Glycolysis

Cytoplasm

Pyruvic acid

Krebs Cycle

Electrons carried in NADH and FADH2

Electron Transport

Chain

Mitochondrion

Substrate level phosphorylation Oxidative phosphorylation


ELECTRON TRANSPORT CHAIN


Matrix

A Cell

One of ItsMitochondria

A Crista

Outer& InnerMembranes

IntermembraneCompartment

MITOCHONDRIA


ELECTRON TRANSPORT CHAINThere are four different complexes

Complex I, II, III, IV,


Peter D. Mitchell

United KingdomGlynn Research Laboratories Bodmin, United Kingdom

b. 1920d. 1992

Mitchell’s hypothesis explains Mechanism of Oxidative

phosphorylation


Energy from oxidation of components in the respiratory chain is coupled to the translocation of hydrogen ions (protons, H+) from the inside to the outside of the inner mitochondrial membrane.

Complexes I, III, and IV acts as a proton pump

Mitchell’s chemiosmotic theory


Complex I and complex III pumps 4 protons each

Complex IV pumps 2 protons To inter-membranous space

10 protons are pumped by the electron transport chain

The transfer of two electrons from NADH+ H+ to O2 is

accompanied by the outward pumping of 10 H+

10 protons are pumped out per NADH 1. 4 must flow in to produce 1 ATP2. The proton-based P/O ratio is 2.5 for NADH as the electron donor and 1.5

(6/4) for succinate


ATP synthase

1. ATP Synthesizing enzyme complex2. Two major components (F0 and F1)3. F1 in all aerobic organisms consists of

- α3β3γδε subunits- binding sites for ATP and

ADP- Catalytic site for ATP

synthesis


P:O Ratio

Number of moles of inorganic phosphate consumed per atom of oxygen utilized

Phosphate group esterifiedP:O ratio =

Electron pairs transferred

Number of moles of inorganic phosphate consumed per atom of oxygen utilized


Paul Boyer (1964) proposed that a conformational change in the mitochondrial membrane protein leads to synthesis of ATP

Paul Boyer hypothesis is now considered as- rotatory motor- engine driving model- binding change model

To explain generation of ATP


In response to proton influx ‘γ’ subunit physically rotates

This induces conformational change in the β3 subunit

β Subunit can adopt different conformationsLoose (L) conformation - (ADP and Pi bind )Tight (T) conformation - (Tightly bound ATP) Open (O) conformation - (Release ATP)

[ATP]


[ADP] [Pi]

[NADH][NAD+]

Increases rate of mitochondrial respiration

Enhanced oxidative phosphorylation

Increased ATP synthesis

Cellular activityATP is used

ADP concentration increased

Increased rate of catabolism of nutrients

Mitochondrial ADP concentration has important role in

regulating oxidative phosphorylation

RESPIRATORY CONTROL

ADP transport across the inner mitochondrial membrane can be inhibited by Atractyloside

It can inhibit oxidative phosphorylation


UncouplersUncouplers is to dissociate oxidation in the respiratory chain from phosphorylation

Compounds are toxic in vivo, causing respiration to become uncontrolled, since the rate is no longer limited by the concentration of ADP or Pi

Uncouplers2,4 dinitro phenolDinitrocresolPentachlorophenolCCCP (m-chlorocarbonyl- cyanide phenyl hydrazine)


Physiological uncouplersThyroxineLong chain free fattyacidsUnconjugated bilirubin

IonohoresValenomycin (Ionophore for K+ ions)Nigercin (Ionophore for K+ ions)

Electron transport chain continues; energy is released as heat


Brown adipose tissue

Characterized by- High content of mitochondria- High content of cytochrome- Well developed blood supply- Relatively rich in carnitine- Has low ATP synthase activity- High oxygen consumption- Involved mainly in metabolism particularly at times when

heat generation is required

Brown color is due to relatively high content of mitochondria


Tissue is extremely active in In some species in arousal from hibernationIn animals exposed to cold (non-shivering thermogenesis)In heat production in the newborn animal

• Shown to be active in normal individuals • Responsible for diet induced thermogenesis

‘Eat and do not get fat


Disorders of mitochondrial function• About 100 polypeptides are required for oxidative phosphorylation

• 13 of these polypeptides are coded by mitochondrial DNA (mtDNA) and synthesized in the mitochondria

Mitochondrial is maternally inherited(Mitochondria from the sperm do not enter the fertilized ovum)

Mitochondrial DNA is about 10 times more susceptible to mutations than nuclear DNA


Characterized by - Accumulation of lactic acid- Myopathies- Cardiomyopathies- Encephalopathies

Mitochondrial Myopathies

• Characterized by the presence of mitochondria with abnormal shape and size• Typically results in muscle fibers appearing as ragged red fibers

( Muscle biopsy; Gomori trichrome or other stains)

May result in cell deathParticularly affect skeletal and cardiac muscles

Courtesy of Dr Ana Sotrel

Gomori trichrome stain. Mitochondrial myopathy.

There are several isolated muscle fibers with red granular staining and

disruption of fiber structure.

http://www.pediatricneuro.com/alfonso/0001%20tip%20ragged%20red%20fibers.htm



A. MRI of the brain showing atrophy and enhancing low attenuation

lesions. B. B. Gomori trichrome stain showing

a ragged red fiber (black arrow) and two severely atrophic denervated

fibers (white arrow).

Mitochondrial encephalomyopathy lactic acidosis stroke like episodes (MELAS)

- Complex I defect; Lactic acidosis, strokes,myopathy,seizures, dementia

Leber's hereditary optic myopathy (LHON) • Characterized by blindness in young males• Caused by a single base mutation in NADH Coenzyme Q

reductase• Streptomycin induced deafness is also found to be due to a

mutation in the mitochondrial rRNA

Myoclonic epilepsy ragged red fiber disease (MERRF)• Myoclonic epilepsy, myopathy, dementia

Leigh's syndrome• Complex I defect; Movement disorders


THANK YOU

oxidative phosphorylation by dr. ashok kumar j

Health & Medicine

atp synthesisdr

atp synthase1

conformation adp

subunit subunit

high content of mitochondria

ionselectron transport

high content of cytochrome

mitochondrial dna mtdna