619 GLA 8/11 pt 2 Oxidative Phoshporylation

What are the two largest ATP producers for most cells?

ETC and complex V

Hypoxia

lack of oxygen to the cells, caused by decreased pO2 of O2 in environmet

Ischemia

blockage in blood vessels that prevents flow of nutrients to tissues (including o2)

2,4-dinitrophenol (DNP)

uncouples oxidative phosphorylation by making the inner mitochondral membrane permeable to protons, leading to increased oxygen consumption without ATP synthesis

Electron Transport Chain

moves electrons along a series of steps to produce energy

Apoptosis

mitochondria can trigger apoptosis by releasing cytochrome c

5 Processes Mitochondria Contain Enzymes For

fatty acid b-oxidation

acetyl-coa production

ketogenesis

tca cycle

oxidative phosphorylation

Cristae

folds made by invaginations of the inner mitochondrial membrane, provide a large surface area for reactions

Outer Mitochondrial Membrane

contains proteins that transport large molecules needed to carry out mitochondrial functions

Mitochondrial Matrix

the lumen surrounded by the inner membrane

Intermembrane Space

space between the outer and inner mitochondiral membranes

Mitochondral Origin

has two membranes because it is theorized to have been caused by an anaerobic eukaryotic call endocytosing an aerobic microorganism

Series of Electron-Carrying Species Embedded in Inner Mitochondrial Membrane for ETC

complexes i-iv

coenzyme q

cytochrome c

What do the electron-carrying species in the ETC do?

receive electrons from reduced compounds made during glycolysis, the tca cycle, and beta oxidation and pass then through the chain

energy released from these electron hand-offs is used to pump protons into the mitochondrial intermembrane smale to create an electrochemical gradient across the inner mitochondrial membrane

Complex I

accepts e- from NADH, oxidizing it from NADH to NAD+, and then trasnfering the e- to coq, which reduces coq

Complex II (Succinate Dehydrogenase)

catalyzes the oxidation of succinate to fumarate via synthesis of FADH2 from FAD, it then transfers the e- from FADH2 to coq

CoQ

takes the e- from complex i and ii through the inner mitochondrial membrane to complex iii

Complex III

accepts the e- from coq and passes them to cytochrome c

Cytochrome C

takes the e- from complex iii and travels through the inner mitochondrial membrane to deliver them to complex iv

Complex IV (Cytochrome Oxidase)

accepts e- from cytochrome c and passes them to O2, forming H2O

O2

final electron acceptor of ETC, the ETC is dependent on the presence of oxygen and will not run without it

Order e- Travel In for ETC

NADH

complex 1

complex 2

coq

complex 3

cytochrome c

complex 4

O2

(complex 5 acts, but it does not interact with the electron)

Complex V (ATP Synthase)

proton channel coupled to an enzyme that catalyzes the conversion of ADP and inorganic phosphate (Pi) to ATP

Proton Channel Function of Complex V

allows protons to move from the intermembrane space into the mitochondrial matrix

this process releases energy because of the gradient of protons between the intermembrane space and the mitochondrial matrix

Chemiosmotic Hypothesis

the coupling of the proton gradient created by ETC to ATP synthase

ATP synthase uses the energy released from protons moving down their electrochemical gradient to synthesize ATP

Proton Pumps

complex i, iii, and iv release energy during electron transfer that is used to pump protons from the mitochondrial matrix to the intermembrane space

(small amt of the energy is lost as heat)

Electrochemical Gradient in Mitochondria

proton pumping from etc causes more H+ in the intermembrane space than the matrix, establishes the gradient that ATP synthase uses to synthesize ATP

Diffusion and Electrical Charge

allows protons to flow from the intermembrane space to the matrix through ATP synthase

Proton Gradient

caused by etc in mitochondria, also represents a gradient of pH becasue pH is reflective of H concentration

More H+ =

more acidic

What is special about complex 2?

it does not pump any protons across the inner mitochondrial membrane, and is encoded by nuclear DNA

Complex Inhibitors

toxic substances that reduce the ability of the etc to pass electrons along its length

5 Complex Inhibitors

rotenone

antimycin a

cyanide

carbon monoxide

oligomycin

Rotenone

complex i inhibitor

Antimycin A

complex iii inhibitor

Cyanide & Cabon Monoxide

compled iv inhibitors

Common Effects of Complex Inhibitors

prevent NADH oxidation

decrease proton motive force

decrease oxygen consumption

Prevent NADH Oxidation

common effect of complex inhibitors, leads to increased intracellular ratios of NADH/NAD+

Decrease Proton Motive Force

common effect of complex inhibitors, ATP production is decreased because of a decrease in the proton gradient to run ATP synthase

Decrease Oxygen Consumption

common effect of complex inhibitors, no electrons reach the end of the etc for oxygen to accept

Oligomycin

inhibits complex v

does not directly prevent electrons from moving down the ETC to O2

Cyanide Poisoning Causes

*house fires (burning plastic)

intentional ingestion

industrial exposure

certain chemicals

Cyanide Poisoning Clinical Presentation

tachypnea without cyanosis or hypoxia, anion-gap metabolic acidosis (caused by increased lactic acid), and a bitter almond-like odor

Cyanide

inhibits complex vi binding to iron on the molecule, thereby inactivating it

prevents cell from using etc for energy production, leading to increased anaerobic metabolism, lactic acidosis, and death

Carbon Monoxide Exposure

improperly vented heaters

fires

interntional exposure

Carbon Monoxide Poisoning Clinical Presentation

headache, altered mental status, coma, red skin, death

What form of iron do CO and Cyanide bind to?

cyanide = fe+3

CO = fe+2

Carboxyhemoglobin

binding of carbon monoxide to fe+2 in hemoglobin, has a high affinity for oxygen so it does not release it and tissues to not receive oxygen

carbon monoxide impacts hemoglobin function and inhibits complex iv

Carbon Monoxide Poisoning Management

treated with 100% oxyegn therapy since oxygen can displace CO2 on heme at high enough concentrations

Coupling

the grouping of the ETCs creation of a proton gradient with ATP production

Uncouplers of Oxidative Phosphorylation

agents that cause dysfunctions of the ETCs ATP-producing ability, ruin the proton gradient by making the inner mitochondrial membrane permeable to protons causing proton equilibriation

disrupts ATP synthesis while allowing the ETC to continue running at a fast rate, generates a lot of heat

Thermogenin

uncoupler in brown adipocytes, faster ETC means more energy releasing reactions and more heat relase

Nonshivering Thermogenesis

uncoupling in brown fat allows babies to generate heat

Pharmacologic Uncouplers

cause increased catabolicm of fats, sugars, and proteins and increased heat production

leads to increased reliance on anaerobic metabolism, resulting in lactic acidosis

can manifest as fever

3 Pharmacologic Uncouplers

dinitrophenol

pentachlorophenol

aspirin

Dinitrophenol

pharmacologic uncoupler, weight loss supplement that uncoupled ETC from ATP production to cause an increase in catabolic pathways that provide reduing equivalents to the ETC

causes breakdown of fats, sugars, and proteins to cause weight loss

Problems with Dinitrophenol

dosage window is small, and overdose is fatal

Pentachlorophenol

pharmacologic uncoupler, industrial pesticide

Aspirin

pharmacologic uncoupler, most common one, uncoupling property at least partially accounts for the hyperthermia that can be seen in asprin overdose

Oxidiative Phosphorylation (Simple)

the conversion of nutrient-derived substrates into usable energy (in the form of ATP) coupled with the ETC

Reactive Oxyen Species Production

naturally produced in cells as byproduct of oxidative phosphorylation, when electrons leak out of the etc and react with molecular oxygen to form superoxide

predominantly occurs at complex i and iii

Superoxide

can be converted to other ROS or reactive nitrogen species

Superoxide Dismutase

enzyme that quickly converts superoxide to hydrogen peroxide

Further ROS Production

hydrogen peroxide is more stable and can diffuse out of the mitochondria to the cytosol, and further reacted to produce hydroxyl radical

Benefial Roles of ROS

cellular signaling, host defense, redox regulation

Harmful Effects of ROS

damage DNA, proteins, and lipids leading to cellular dysfucntion, apoptosis, and oxidative stress

this oxidative sress is implicated in aging, many pathological conditions, and carcinogens

Antioxidant Enzymes & Non-Enzymatic Antioxidants

help neutralized ROS and mitigate potential damage

3 Antioxidant Enzymes

superoxide dismutase

catalase

glutathione peroxidase

2 Non-Enzymatic Antioxidants

vitamin e

vitamin c

Superoxide Dismutase

antioxidant enzyme, catalyzes the conversion of superoxide anion into hydrogen peroxide and molecular oxygen

3 types - cytoplasmic, mitochondrial, secreted out of the cell

Catalase

antioxidant enzyme, in peroxisomes, rapidy converts hydrogen peroxide into water, in the presence of transition metals this can lead to the generation of highly reactive hydroxyl radical

Glutathione Peroxidase (GPx)

enzyme that catalyzes glutathoine reduing of ROS

Glutathione

tripeptide antioxidant, in cytosol, neutralizes ros by acting as a reducing agent

becomes oxidized during the process of reducing peroxide and must be regenerated

Glutathione Reductase Action

uses NADPH as an electron donor to regenerate reduced glutathione, which can then go and neutralize another molecule of peroxide

Pentose Phosphate Pathway

crucial for generating NADPH, deficiencies in this pathway can make cells more susceptile to oxidative damage

Oxidative Phosphorylation Summary

While oxidative phosphorylation is a critical metabolic process producing ATP, it can inadvertently lead to ROS formation. When there's an imbalance between ROS production and the cell's antioxidant defense mechanisms, oxidative stress occurs. This can lead to damage and, over time, can contribute to aging and various pathological conditions. In recent years, mitochondria-targeted antioxidants have been explored as potential therapeutic agents to counteract ROS production and its detrimental effects.

What are the major sites for ROS to act in the ETC?

complex i

complex iii