22 oxidative phosphorylation

Purpose of oxidative phosphorylation step?

To produce ATP by using energy derived from H+ gradient created in ETC (Major ATP-yielding step of aerobic respiration)

What is the role of mitochondria in oxidative phosphorylation?

Mitochondria serve as the site for oxidative phosphorylation

• mitochondrial matrix convert e- (reduction potential) into a H+ gradient across the inner membrane, then into ATP

What is the protonmotive force? (pmf)

Pmf is the electrochemical gradient of H+ across the inner membrane, driving ATP synthesis in oxidative phosphorylation

• pmf represents a large reservoir of potential energy

Why is pmf useful?

Concentration gradient makes transporting an e- back to matrix a thermodynamically favorable process

How many protons are pumped for each pair of e- that enters ETC from NADH?

10 protons per NADH

4H+ complex I, 4H+ Q, 2H+ complex IV

What catalyzes the formation of ATP from ADP+P?

ATP synthase is the enzyme that catalyzes the formation of ATP from ADP and inorganic phosphate (P). It utilizes the energy from the pmf & proton gradient

What is the structure of ATP synthase?

ATP synthase is a complex enzyme made up of two main components:

1. F0 portion: embedded in the membrane that forms a H+ channel (subcomplex)

2. F1 portion: that extends into the mitochondrial matrix, where ATP is synthesized (knobs)

Stator vs rotor portions of ATP synthase

Rotor: spinning portion. coiled c-y subunit

Stator: stationary portion. provides support/connects. a/b hexamer

What drives rotation of C-ring? How does it occur?

Protonation/re-ionization of glutamate drives rotation

How?

1. C-ring rotates next to a neg charged glut which gets titratable H+

2. 1st glut rotates and reaches 2nd half channel connected to matrix.

3. Reaches Arg & makes glut loose H+ & become neg charged again (favorable electrostatic interaction)

4. H+ gradient created! H+ from inner membrane to matrix!

What are the 3 conformational changes created by rotation of y-subunit inside the central channel?

1. open: releases bound ADP and inorganic phosphate

2. loose: holds ADP and phosphate together

3. tight: catalyzes the formation of ATP

120 degrees changes conformation. 1 full rotation is 360 degrees which produces 3 ATP. (all driven by H+ energy gradient which is thermodynamically favorable)

Endergonic vs exergonic processes in oxidative phosphorylation

exergonic(release energy) transport of H+ down electrochemical gradient is coupled to endergonic(require energy input) ATP synthesis

How is ETC, electrochemical proton gradient, and ATP synthesis all tightly coupled?

1. oxidative phosphorylation in mitochondria enables flux of pathway

2. ETC/oxygen consumption is linked to substrate availability

3. direct coupling of ATP synthase w ETC

IF ATP CANT BE MADE/NO SUBSTRATE AVAILABLE, ETC STOPS

What blocks/prevents ATP synthesis by shutting down e- transport?

Oligomycin is a potent inhibitor that binds to Glut in C-ring of ATP synthase, preventing protons from passing through to matrix and halting ATP production. (H+ gradient becomes too steep in intermembrane space)

What is respiratory control?

Respiratory control refers to the regulation of oxidative phosphorylation, where ATP production is closely tied to the availability of ADP and substrate. When ADP levels are low, the ETC slows down, reducing oxygen consumption and ATP synthesis.

How does DNP uncoupling differ from regular ATP synthase?

DNP (2,4-dinitrophenol) allows H+ to dissipate the electrochemical gradient/pmf without passing through ATP synthase, leading to decreased ATP production despite ongoing electron transport and increased oxygen consumption.

Can regulated uncoupling be useful sometimes?

Yes, regulated uncoupling can be beneficial for thermogenesis, producing heat instead of ATP, which is important in certain physiological conditions like hibernation or in brown adipose tissue.

• expresses uncoupling proton I to short circuit H+ gradient & allows then to fall back in

How much ATP produced in glycolysis vs aerobic respiration?

1. Glycolysis: glucose to lactate = 2 ATP

2. Aerobic resp: glucose to CO2 = 32 ATP