Oxidative Phosphorylation

what are the 2 phases of the Oxidation of fuels

1. production of reduced NADH and FADH2

2. use of generated energy to produce ATP = oxidative phosphorylation

Energy production steps

1. electrons flow from NADH and FADH2 through a series of carriers to reach O2

2. energy produced during the transfer of electrons in the electron transport system is used to pump protons into the intermembrane space

3. Energy produced when these protons reenter the mitochondrial matrix is used to synthesize ATP

4. Electron transport chain coupled with ATP synthesis=oxidative phosphorylation

Mitochondrial transport of reducing agents (2)

Glycerol 3-P shuttle (NADH→FADH2)

- Electrons are transferred from NADH to DHAP by cytosolic glycerol 3-P dehydrogenase

- Glycerol 3-P is oxidized by the mitochondrial isoenzyme and FAD is reduced to FADH2

Malate shuttle (NADH→NADH)

- Oxaloacetate is reduced to malate with use of NADH

- Malate enters the mitochondria and is oxidized to oxaloacetate with reformation of NADH

ATP/ADP transport (2)

- Adenine nucleotide antiporter imports 1 ADP from cytosol, while exporting 1 ATP into the cytosol

- Phosphate transporter carrier phosphate form the cytosol into the matrix

Whare is the ETC located?

inner mitochondrial membrane

what is the structure of the ETC

- 4 large multiprotein complexes (I-IV)

- 2 small carriers: coenzyme Q (CoQ) and cytochrome c

- Carriers transfer electrons between complexes, to finally combine with O2 and H+ → H20

What is Complex I in ETC

NAHD:CoQ oxidoreductase (dehydrogenase) is a giant protein complex embedded in the IMM

- Energy is lost with each passing and is used to pump 4H+ from the matrix into the IMS

What is Complex II in ETC

Succinate dehydrogenase oxidizes succinate to fumarate (TCA cycle), with production of FADH2

- No energy is lost in this process → No protons are pumped at this stage

- Parallel entry for electrons into the ETC

- Electrons are passed to CoQ one at a time

What is Coenzyme Q=ubiquinone (4)

1. CoQ is a quinone derivative from cholesterol

2. Only lipid-soluble and non-protein-bound component of ETC

3. CoQ = mobile carrier of electrons from complexes I and II to complex III

4. Carrier 2 electrons at a time

Complex III process and description

- Cytochrome bc1

• - 2 electrons from ubiquinone → cytochrome b → cytochrome c1 → cytochrome c

-Cytochrome c

• - mobile electron carrier that brings electrons to complex IV, one electron at a time

- High drop in energy with electron movement → 4H+ are pumped into the IMS

Complex IV Description and Process

- Cytochrome a + a3 (cytochrome oxidase)

• - Conducts electrons through cytochromes a and a3, finally reducing one molecule of oxygen

• - When 4 electrons are available, 4 protons are used to reduce and split O2 to form 2 molecules of H2O

• - In the process, 2H+/H2O from the matrix are pumped into the IMS

How many electrons can O2 accept?

4 electrons

How many steps can oxygen be reduced in?

4 steps

How is superoxide formed?

when CoQ accidentally interacts with O2

describe ROS

partially reduced oxygen is very unstable and avid for electrons

What causes oxidative stress

imbalance between the production of ROS and removal mechanisms

Examples of imbalances that cause oxidative stress

- Lipid peroxidation

- Proteins oxidization and degradation or aggregation

- DNA damage (base oxidation or double strand breaks)

Cellular defense against oxygen toxicity

- Enzymes (glutathione peroxidase, catalase, superoxide dismutase)

- Antioxidants (vit, A, C, E)

What do ETC inhibitors do?

Block the flow of electrons to oxygen and inhibit ATP synthesis

The energy needed to phosphorylate ADP to ATP is produced by a flow of protons against an _________

electrochemical gradient

The proton gradient is established by what?

H+ pumped from the matrix into the IMS using the energy released by the electron transport through complexes I, III, and IV

What is ATP synthase made of (domains)

- Membrane domain (F0) embedded in the IMM

• - Rotor

• - H+ - channel

- Extramembraneous domain (F1) as a sphere that protrudes into the matrix

• - Head = 3 aB-subunit, each B subunit with catalytic site

ATP synthesis steps

1. H+ from the IMS reenters the matrix by passing through the H-channel in the F0 domain, driving the rotation of the c ring

2. this causes conformational changes the aB-subunits of the F1, exposing the catalytic side: ADP + Pi → ATP

3. One complete c ring rotation produces 3 molecules of ATP

Oxidative phosphorylation summary

1. NADH and FADH2 are oxidized via mitochondrial electron transport chain

2. An electrochemical proton gradient is established across the inner mitochondrial membrane

3. The proton gradient drives ATP synthesis

4. inhibitors of electron transport block ATP synthesis

Requirements for Oxidative Phosphorylation

1. Electron donors: NADH, FADH2

2. Electron acceptor: O2

3. Intact mitochondrial membrane

4. Functional ETC components

5. ATP synthase

ATP synthesis and ETC are _____ in normally functioning mitochondria

coupled

If ATP synthase is inhibited or has inadequate supply of ADP what will happen?

1. ATP synthesis is inhibited

2. O2 will not be consumed

3. ETC components accumulate in reduced states

What does Oligomycin do?

binds to the F0 domain, closing the channels and preventing the reentry of H+ into the matrix → inhibited ATP synthesis and blocked oxidative phosphorylation

What does uncoupling proteins in the IMM do?

form channels that allow H+ to reenter the matrix without synthesis of ATP

What results form Uncoupling proteins? (3)

- ATP production decreases and O2 consumption and ETC rate increase

- Energy is releases as heat in non-shivering thermogenesis

- UPC1/thermogenin is responsible for heat production in the mitochondria-rick brown adipose tissue

What is Dinitrophenol and what does it do?

- Lipophilic H+-carrier that disrupts the proton gradient by carrying protons across the IMM

How many proteins involved in OP are encoded by mtDNA and synthesized in the matrix?

13

How much greater is the mutation rate of mtDNA than nuclear DNA and what does it cause?

10x greater, causes genetic defects in OP enzymes

Hereditary defects are very rare and result in lactic acidosis and muscle and nerve pathology, what do these tissues have in common?

these are tissues with high ATP requirements

What is Leber’s hereditary optic neuropathy?

Complex I defect

- bilateral neuroretinal degeneration with optic nerve damage

What is Leigh syndrome?

F0 defect

- optic nerve atrophy, hypotonia, ataxia, respiratory abnormality