Course:SOMBlock3IQ1/Week 1/Case 4 Oxidative Phosphorylation
Goal: The goal of this case is to understand oxidative phosphorylation and how it is regulated.
[edit] Learning Objectives
1. Explain the role of oxidative phosphorylation in metabolism and fuel utilization.
- Ox phos uses the energy from high energy e- to pump H+ against their gradient. The e- are transferred from various e- carriers to O2. The H+ gradient is used to provide energy to produce ATP.
2. Draw the path of electrons from reduced electron carriers to O2 in the electron transport chain as well as the major complexes and mobile carriers in the pathway. 3. Explain how electron transport is coupled to H+ transport across the mitochondrial inner membrane and list the electron transport reactions that result in H+ ejection.
- Coupling of high energy e- transport to H+ ejection. Complex I, III, IV eject H+.
4. Explain how electron transport and ATP synthesis are coupled.
- Coupled via the electrochemical gradient of the H+ gradient.
5. Explain how the rate of oxidative phosphorylation is regulated by respiratory control and how this process limits energy utilization.
- Respiratory control is the regulation of ox phos rate by ADP levels; Pi & O2 availability also participate.
6. Define brown adipose tissue and contrast it to white adipose tissue.
- Brown adipose tissue utilizes uncoupling to generate heat; it is specialized for nonshivering thermogenesis. Uncoupling allows H+ to travel with its gradient, reducing the electrochemical gradient. It has numerous mito, fat droplets, & large amount of uncoupling protein (UCP or thermogenin). White adipose tissue is a storage, energy, and hormone producing/releasing molecule. It helps with movement and provides padding. Each cell contains one large fat droplet.
[edit] What cells is oxidative phosphorylation occurring in?
[edit] What cells have a higher concentration of mitochondria?
[edit] What cells have the highest affinity for O2?
[edit] What levels of O2 sat does oxidative phosphorylation shut down?
[edit] Other ATP production options
[edit] Effect of supplements on oxidative phosphorylation
[edit] What is creatine and its function?
The strength of ATP is that it has intermediate phosphoryl transfer potential. It has a low enough energy state to readily receive phosphate groups from other molecules yet has a high enough energy state to supply its phosphoryl group and provide free energy for reactions.
Creatine phosphate is stored in small amounts in muscle and is the immediate source of phosphoryl groups for the replenishment of ATP in working muscle. The phosphate is transferred to ADP (spent ATP) to regenerate ATP.
This graph shows the source of ATP during exercise. The pre-existing supply of ATP is used within seconds, and the creatine phosphate supply is only capable of regenerating ATP for a few seconds more. Anaerobic metabolism is the oxidation of glucose in glycolysis. Aerobic metabolism is the oxidation of acetyl CoA from glucose and FFA in the citric acid cycle.
NB Source: Stryer biochem
[edit] What is carnitine and its function?
Carnitine shuttles FFAs into the mitochondri for beta-oxidation. FFAs are activated by combining with CoA to from acyl CoA. Carnitine acyltransferase I, located on the outer mitochondrial membrane, transfers the FFA from acyl CoA to carnitine, forming acyl carnitine. The acyl carnitine is then transolcated across the mitochondrial membrane into the matrix in exchange for carnitine. Carnitine acyltransferase II transfers the FFA back from the acyl carnitine to CoA, regenerating acyl CoA and carnitine.
NB Source: Stryer biochem
[edit] What is Q10 and its function?
Q10 is the most common ubiquinone, or Co-enzyme Q, in human mitochondria. Ubiquinones participate in the electron transport chain. Particularly, they are involved in the Q cycle of complex III. Ubiquinone is reduced by complexes I or II.
Devlin
Q10 is also offered as an anti-oxidant vitamin. There are few reported side-effects, but this compound is not sanctioned by the FDA yet.
http://www.coenzymeq10supplement.com/side-effects-of-coenzymeq10.htm
JT
[edit] What is DNP?
- DNP is a lipophilic proton carrier; it diffuses easily through the mitochondrial membrane
[edit] How it prevents production of ATP?
- Due to the fact that DNP can diffuse readily through the mitochondrial membrane, it causes electron transport to proceed at a rapid rate without establishing a proton gradient. Therefore, energy is released as heat instead of being utilized to make ATP.
[edit] Other un-couplers?
- In high doses, aspiring serves as an uncoupler of oxidative phosphorylation. The energy release as heat explains the high fever the accompanies large overdoses of aspirin.
- UCP1 (thermogenin) is responsible for the activation of fatty acid oxidation and heat production in the brown adipocytes of mammals.
[edit] How do un-couplers work?
- Electron transport and phosphorylation can be uncoupled by compounds that increase the permeability of the inner mitochondrial membrane to protons. Uncouplers essentially create a "proton leak," meaning they allow protons to re-enter the matrix without being used to synthesize ATP.
[edit] If he wasn’t taking DNP would he still have the same symptoms?
- DNP serving as an uncoupler is likely the source of his feber and sweating.
EB - Stryer, ed. Biochemistry, NCBI bookshelf
[edit] What are the causes of his symptoms?
[edit] Differential diagnosis
[edit] Physiology of brown fat
Brown adipose tissue activity causes nonshivering thermogenesis. It is highly vascularized. Norepinepherine stimulates the differentiation and proliferaiton of brown adipocytes and the production of uncoupling protein-1 (UCP-1, AKA thermogenin). UCP-1 uncouples the oxidation of NADH and FADH2 by the electron transport chain and the phosphorylation of ADP to ATP by dissipating the H+ concentration gradient across the inner mitochondrial membrane. The energy is released as heat which warms the blood of the BAT vasculature.
NB Source: Ross histology, Stryer biochem
[edit] What are the other types of fat?
[edit] What is rotenone
- Rotenone is an insecticide; however, it can interfere with oxidative phosphorylation because it blocks electron transfer from substrate to oxygen. More specifically, it blocks the transfer in NADH-Q oxidoreductase, resulting in the inability of NADH to be used as a substrate
- However, in this situation, electron transfer from the oxidation of succinate can still function because these electrons enter through QH2, past the block.
EB, Stryer, ed. Biochemistry, NCBI bookshelf
[edit] Are there pesticides that affect oxidative phosphorylation?
[edit] Class Notes
Case 4 – Oxidative Phosphorylation
Oxidative Phosphorylation
- What’s going on?
- Oxidation – series of redox reactions that move electrons down the ETC, providing energy to pump protons out of the mitochondrial matrix, establishing an electrochemical gradient
- Consists of various complexes and electron carriers
- Complex I – NADH dehydrogenase; accepts electrons from NADH; first go to FMN then Fe-S centers; can only accept two electrons
- Complex II – succinate dehydrogenase; succinate is oxidized to fumarate (in the TCA cycle which is associated with complex II in the membrane), transferring two electrons to FAD (also part of the TCA cycle), which becomes FADH2 and transfers electrons to coenzyme Q from within the complex; can only accept two eletrons
- Coenzyme Q – lipid that shuttles electrons within the membrane from complexes I and II to complex III; transfers electrons one at a time (but carries a pair) in the Q cycle
- Complex III – accepts one electron at a time from coenzyme Q via cytochromes (b and c1). Cyctochrome c is a freely diffusible molecule that transfers electrons between complexes III and IV along the intermembrane side of the membrane; transports four protons across the membrane for each pair of electrons
- Complex IV – also uses cytochromes for carrying electrons; once four electrons are collected, oxygen is reduced to water; two protons are pumped across the membrane in the process; during the reduction of oxygen, reactive oxygen species (ROS) may form and cause damage
- Two cycles through the ETC are necessary to reduce one molecule of O2 to H2O
- Consists of various complexes and electron carriers
- Phosphorylation – protons cross back into the matrix along the electrochemical gradient, providing energy for the synthesis of ATP from ADP and Pi
- Complex V – F-type ATPase consists of F0 and F1; F0 is in the membrane and F1 projects into the matrix; ADP and Pi binds to one of three domains on F1 that undergo conformational changes, that favor the binding of ADP and Pi (L state), then the creation of ATP (T state), then the release of ATP (O state); one rotation of F0 creates three ATPs from F1 and uses 12-13 protons
- What cells is oxidative phosphorylation occurring in?
- All cells but RBCs
- What cells have a higher concentration of mitochondria?
- Skeletal muscle – specifically slow twitch fibers
- What cells have the highest affinity for O2?
- Cardiac cells, slow twitch muscle fibers (?)
- Oxidative phosphorylation is regulated by respiratory control, i.e., the amount of ADP available for phosphorylation, and also other substrates necessary to produce ATP, including phosphate and oxygen
- Keep in mind that the TCA cycle and oxidative phosphorylation are integrally linked and the rate of one affects the rate of the other
- Oxidation – series of redox reactions that move electrons down the ETC, providing energy to pump protons out of the mitochondrial matrix, establishing an electrochemical gradient
- What levels of O2 sat does oxidative phosphorylation shut down?
- We’re not sure
- Other ATP production options
- Glycolysis – 2 ATP
- TCA cycle – 1 GTP --> 1 ATP
- Effect of supplements on oxidative phosphorylation
- What is creatine and its function?
- Storage and transmission of phosphate-bound energy in the brain (and muscle); taking creatine increases stores of creatine phosphate which rephosphorylates ADP as ATP is used
- Gives only a short burst of energy
- Causes water retention
- What is carnitine and its function?
- Transports acyl CoA into the mitochondrial matrix where it is converted to acetyl CoA
- Facilitates metabolism of carbs
- What is Q10 and its function?
- This is coenzyme Q in the ETC
- Also functions as an antioxidant (prevents the formation of free radicals and so hopefully cancer which can occur due to free radical damage of DNA)
- Not FDA-approved; used as a supplement
- What is creatine and its function?
- What is DNP?
- DNP is a lipophilic proton transporter that binds protons in the intermembrane space and releases them in the matrix, disrupting the electrochemical gradient established by the ETC
- How it prevents production of ATP?
- Uncouples oxidation from phosphorylation; the energy created by the electrochemical gradient is no longer present and so ATP is not made at the same rate
- Other un-couplers?
- How do un-couplers work?
- Uncouplers create leaks through which protons are brought back into the matrix so that protons are no longer used to make ATP in the same amounts; when phosphorylation is uncoupled from oxidation, the energy is released as heat
- Metabolism speeds up because the body tries to compensate for the uncoupling by burning fat
- If he wasn’t taking DNP would he still have the same symptoms?
- What are the causes of his symptoms?
- Differential diagnosis
- Diabetic ketoacidosis
- MI
- Possibly hyperthyroidism
- Physiology of brown fat
- Uses uncouplers (UCP1, aka thermogenin) to uncouple phosphorylation from oxidation and release energy as heat
- Found in newborns (maybe 10% of all their fat?), but adults have almost none; important for neonates to regenerate heat since they have a high surface area to volume ratio and lose heat easily and also because they cannot shiver; decreases throughout the first decade of life
- Contains numerous small triglyceride droplets that makes it appear brown (because of mitochondria and extensive vascularity of brown adipose tissue); 20% lipid
- Only function is thermogenesis
- Seven specific deposit sites
- What are the other types of fat?
- White adipose – contains one large lipid droplet, which makes it appear white; 80% lipid
- Functions in energy storage, padding, movement
- Ubiquitous in the body
- White adipose – contains one large lipid droplet, which makes it appear white; 80% lipid
- What is rotenone
- Blocks electron transfer from Complex I (specifically FMN/Fe-S centers) to Coenzyme Q; Complex II is not affected, so electrons can be transferred down the chain from there; but NADH buildup would inhibit the TCA cycle so adequate FADH2 would not be produced to keep the chain going
- Are there pesticides that affect oxidative phosphorylation?
Learning Objectives:
- Explain the role of oxidative phosphorylation in metabolism and fuel utilization.
- Draw the path of electrons from reduced electron carriers to O2 in the electron transport chain as well as the major complexes and mobile carriers in the pathway.
- Explain how electron transport is coupled to H+ transport across the mitochondrial inner membrane and list the electron transport reactions that result in H+ ejection.
- Explain how electron transport and ATP synthesis are coupled.
- Explain how the rate of oxidative phosphorylation is regulated by respiratory control and how this process limits energy utilization.
- Define brown adipose tissue and contrast it to white adipose tissue.