M2C Unit 2 Lesson 4

Oxidative phosphorylation accounts for almost __ of the ATP generated by cellular respiration

90%

HOW MANY ATP ARE MADE FROM TOTAL REDUCTION OF O2 TO H2O?

3 ATP

HOW DOES OXPHOS PRODUCES ENERGY IN THE FORM OF ATP FROM NADH OR FADH2 ?

Proton gradient created by electron transport drives cellular work.

What are the 2 mobile carriers in ETC?

lipid soluble CoQ and water soluble protein Cyt c

Order in which electrons and transfered in ETC

NADH → complex I → CoQ → complex III → cyt c → complex IV →O2

What is Complex I in ETC?

NADH dehydrogenase

What is Complex II in ETC?

FADH2 = Succinate dehydrogenase

What does Complex I do?

• Accepts electrons from NADH

• Transfers electrons to Coenzyme Q (ubiquinone)

• Pumps 4 H⁺ into the intermembrane space

What does complex II do?

• Accepts electrons from FADH₂ (via succinate → fumarate reaction)

• Transfers electrons to Coenzyme Q

• Does NOT pump protons

• lowest ATP yield

What is Complex III?

Cytochrome bc1 complex

What does complex III do?

• Transfers electrons from CoQ (ubiquinol) to cytochrome c

• Pumps 4 H+

What is complex IV?

Cytochrome c oxidase

What does complex IV do?

• Transfers electrons from cytochrome c

• Final electron acceptor: O₂ → H₂O

• Pumps 2 H⁺

What does Coenzyme Q (Ubiquinone) do?

Moves electrons from Complex I & II → Complex III

What does Cytochrome c do?

Moves electrons from Complex III → Complex IV; Water-soluble (on outer surface of inner membrane)

What are the two pathways of etc?

NADH → I → Q → III → Cyt c → IV → O₂
FADH₂ → II → Q → III → Cyt c → IV → O₂

What is complex V?

ATP synthase

What does Complex V do?

uses proton gradient but is NOT part of ETC proper

CoQ also accepts electrons from the FADH2 generated during what?

• fatty acid oxidation via the fatty acyl-CoA dehydrogenases

• mitochondrial glycerol-3- phosphate dehydrogenase of the glycerol phosphate shuttle

What is the pH of the intermembrane space in etc?

Low pH

What is the pH of the mitochondrial matrix in etc?

high pH

What is the proton-motive force?

the H+ gradient

What is F1 of ATP synthase?

ATP synthesis unit, Located on the matrix side, makes ATP

What is F0 of ATP synthase?

Located in the inner mitochondrial membrane. Forms a rotating channel for H⁺ (protons). Allows protons to flow from the intermembrane space → mitochondrial matrix

• Flow of protons

WHERE DOES THE ADP COME FROM?

ADP and ATP Transporter

What is ATP/ADP antiporter?

ATP/ADP translocase= Adenine nucleotide translocase or carrier

ARE THERE MOLECULES THAT INTERFERE WITH OXPHOS?

Inhibitors and Uncouplers

What are Inhibitors of Respiratory Chain?

Bind to one of the complexes in the electron transport chain and stop oxidation-reduction reactions and electron transfer.

What are Uncouplers in oxidative Phosphorylation

• Break the link between the rate of electron transport and the synthesis of ATP.

• A success of chemiosmotic theory was that it could explain “uncouplers”.

What does Atractyloside do?

prevents transport and availability of ADP in matrix for ATP synthesis (antiport of ATP/ADP into matrix)

Atractylis gummifera is easily confused with what?

a wild artichoke

What is Amytal (amobarbital)?

• also known as truth serum, is a barbiturate.

• used in the treatment of anxiety, insomnia, and epilepsy.

• a reversible inhibitor of NADH dehydrogenase (Complex I) of the respiratory chain

Blockade of electron transport chain with amytal has been shown to?

protect cardiac muscle during ischemia-reperfusion by limiting the production of ROS

What is Rotenone?

• Naturally occurring pesticide

• Also known as fish poison

• Potent inhibitor of NADH dehydrogenase (Complex I) of the mitochondrial electron transport chain

Effect of Retenone

No NADH can be oxidized (Complex I inhibition), but succinate can still enter the chain and lead to some electron transport and reduced amounts of ATP.

What is Antimycin?

• An inhibitor of complex III.

  • Binds tightly to cyt b in the reduced state.

  • Stops electron transport à no ATP is produced

• Complex I, CoQ, complex II and cyt b of Complex III are fully reduced

• Cyt c and complex IV are fully oxidized

What complex does Antimycin inhibit?

Complex III

What complex of ETC does Rotenone inhibit?

NADH dehydrogenase (Complex I)

What complex of ETC does Amytal (amobarbital) inhibit?

NADH dehydrogenase (Complex I)

What complex of ETC does CO inhibit?

Complex IV

What complex of ETC does Cyanide inhibit?

Complex IV

What complex of ETC does Oligomycin inhibit?

Complex V (ATP synthase)

Cyanide (CN) binds to the oxidized form of the heme iron in what cytochrome?

Cytochrome a3

Cyanide prevents iron from converting to its active form which is?

Fe+2 (stuck at Fe+3 due to cyanide)

Nitrite followed by or thiosulfate treatment is the treatment for?

Cyanide (CN) Poisoning

CN binds to the oxidized or ferric (Fe3+) form of iron in the heme of the cytochrome-a3 component of Complex IV and prevents?

O2 reduction

What happens to Mitochondrial respiration and ATP production in CN poisoning?

both cease resulting in rapid cell death

If caught early, nitrites can convert Fe2+ in hemoglobin into Fe3+, resulting in the formation of ____ , which competes for binding of CN to Complex IV.

methemoglobin

Subsequent administration of thiosulfate allows enzymatic conversion of CN to _____, which is less toxic and excreted in urine.

thiocyanate

What competes with O2 for binding to reduced heme-a3 (Fe2+) in Complex IV?

Carbon monoxide

What binds to the oxidized form of heme-a3 (Fe3+).

Cyanide

What binds to the Fo portion of ATP synthase, blocks the proton pathway in Fo and prevents the re- entry of protons into the matrix of the mitochondria?

Oligomycin

When what part of ETC is inhibited does the proton gradient builds up?

ATP synthase

Inhibition of ATP formation by oligomycin prevents what type of reactions?

oxidation-reduction

What are Uncouplers?

Molecules that allow protons to reenter the mitochondrial matrix from the intermembrane space independent of the proton-channeling function of ATP synthase

If the proton gradient is disrupted, then phosphorylation of ADP is?

uncoupled from the transfer of electrons.

When phosphorylation of ADP becomes uncoupled from the transfer of electrons, what happens?

Resulting reduction in the proton gradient

• fast respiration rate due to higher ADP than ATP

When uncoupler reaction of ATP synthase occurs, what happens to TCA and electron transfer to O2?

accelerated

If ATP synthase is inhibited, the flow of protons across the membrane produce what?

heat

What are Membrane-damaging agents where OxPhos cannot occur efficiently in mitochondria with damaged inner mitochondrial membranes because this will render them permeable to proton?

• cytosine arabinoside (AraC)

• azidothymidine (AZT)

What is the effect of Mobile proton carriers (Certain lipid-soluble substances bind to and transport protons through the inner membrane) on ATP production?

They transport protons across the inner mitochondrial membrane, bypassing ATP synthase.

How does DNP uncouple oxidative phosphorylation?

It carries protons across the inner mitochondrial membrane, collapsing the proton gradient.

Why can DNP cause hyperthermia (overheating)?

Energy from the ETC is released as heat instead of being used to make ATP.

At toxic doses, how does aspirin affect oxidative phosphorylation?

It acts as an uncoupler by transporting protons across the inner mitochondrial membrane.

What are Proton channels uncouplers in ETC/Ox Phos?

These are proteins that create pathways for protons to flow back into the matrix without ATP synthase.

What is the major physiologic uncoupling protein?

Thermogenin (UCP1).

Where is thermogenin found?

Brown adipose tissue of newborns to serve exclusively for generating heat.

What is the function of thermogenin?

Generates heat by dissipating the proton gradient.

What is Thermogenin (also known as UCP1) ?

naturally occurring uncoupler in humans and hibernating animals

Where is UCP present in adults?

supraclavicular and paravertebral areas

Where is UCP present in infants?

Posterior neck

What is Thermogenesis?

heat production and maintenance of body temperature

What is Local contraction of muscles uses up ATP and generates heat, since no external work is done?

Shivering

What is the effect of shivering?

Decrease in ATP levels speeds up respiration due to respiratory control, generating heat as well as ATP.

What do non-shivering thermogenesis use to generate heat?

Use uncoupling to generate heat!

Brown adipose tissue (BAT) main function?

specialized for heat production

White adipose tissue (WAT) main function?

specialized for energy storage

What is Leptin?

secreted by the white adipose tissue as an appetite-suppressing hormone

Effect of fatty acid on UCP-1?

activtes it

HOW IS NADH MADE IN THE CYTOPLASM GET IN THE MITOCHONDRIA FOR OXPHOS?

Malate/Aspartate Shuttle and Glycerol Phosphate Shuttle