Electron Transport and Oxidative Phosphorylaton Flashcards
Whats an overview of oxidative phosphorylation?
Cellular respiration its the third step where the reduced NADH and FADH2 are exchanged for ATP
IS NOT substrate level of phosphorylation
All happens in mitochondrial matrix and inner mitochondrial membrane
**most of the oxygen we breath in is utilized by ETC
What is the role of coenzyme Q (CoQ) in the ETC?
It transports electrons from complex 1 and complex 2 to complex 3
What is the role of Cytochrome c (CytC) in the ETC?
It transports electrom from complex 3 to complex 4
Where are the complexes located?
There are 4 of them
Complex 1-3 are located in the inner mitochonrdrial membrane
Complex 2 is embedded in the membrane but doesnt span the inner membrane
**they are all proton pumps
What is oxidative phosphorylation (OXPHO)
ETC + ATP synthase are what create the OXPHO system
The ATP synthase generates ATP thro electrochemical (proton) gradient formed by the ETC which is composed of complex 1-4 and complex 5 is the ATP synthase
**all the complexes are mutlisubunit enzymes
What is complex 1 of OXPHO?
NADH-Q reductase
Its the oxidation of NADH (electrons transferred from NADH to complex 1)
CoQ then carries them from complex 1 to complex 3
**it also moves four protons across the mitochondrial membrane to set up a proton gradient
its a proton pump
What is the environment in terms of charge of the mitochondrial matrix and intermembrane space?
the mitochondrial matrix is more neg charged and the intermembrane space is more positively charged
Why is CoQ 10 important? and how does taking a statin effect it?
Statins will reduce the amount of CoQ10
The problem is that CoQ10 plays a major role in ATP production in the mitochondria
What happens in complex 2 of OXPHO?
Succinate dehydrogenase complex, Oxidation of FADH2
Its a membrane that contains succinate dehydrogenase which causes succinate to become fumarate in the TCA cycle which produces FADH2
The purpose of this step is to accept elextrons for FADH2 and transfer electrons into ETC (CoQ, plays a big role in collecting the electrons)
** NOT a proton pump (doesnt move protons across the membrane)
What happens in complex 3 of OXPHO?
Cytochrome C reductase (Oxidation of CoQ)
CoQ transfers the electrons to complex 3 which then transfers them to Cytochrom C
**it is a proton pump and pumps 2 protons across, here the inter-membrane spaces becomes even more positive
What is the role of cytochrome c?
A heme-containing protein. its the heme that carries electrons in cytochome c.
When a cell receives an apoptotic signal, cytochrome c is released into the cytosol and triggers programed cell death thro apoptosis
What happens in complex 4?
Cytochrome C oxidase
It catalyzes the transfer of electrons from cytochrome c to molecular O2
This creates a negatively charged oxygen so it reacts with H+ to produce H2O
**this charged O2 is a major source of superoxide in our body
complex 4 is the last and third proton pump of the ETC, the ETC ends here
What is a superoxide and why is it important for us?
A superoxide is a charged O2 which is created during the ETC (complex 4)
Its important because it can then be used to bind to free radicals (H+) which must be removed from our bodies to protect us
What is complex 5?
ATP synthase
The electrochemical gradient is coupled to the ATP synthase, which means that the spontaneous passage of protons thro the ATP synthase complex as they enter the mitochondrial matrix drives the formation of ATP
What is the F0 Pore of the ATP synthase?
Its the membrane-embedded portion of ATP synthase
What are the c subunits of the ATP synthase?
Part of the F pore, these form a rotor that rotates as protons from the inner-membrane space bind a c-subunit and enter the mitochondrial matrix
What are the A and B subunits of the ATP synthase?
They are embedded in the inner membrane and is NON-ROTATING subunit
What is the Y subunit?
Rotating protein shaft that connects the F0 pore to the F1 headpiece. the Y subunits rotation is driven by the c subunits
What is the F1 headpiece of the ATP synthase?
It extends into the mitochondrial matrix and consists of 3 pairs of aB subints
What are the aB subunits of the ATP synthase?
Each aB pair binds ADP and Pi (inorganic phosphate) and using mechanical energy, catalyzes the formation of ATP
What are the components of Oxidative Phosphorylation within the ATP synthase (overview of what happens)?
- proton binds to the c subunit and passes to the matrix space
- This causes slight rotation of the C subunit rotor
- The next C subunit in the rotor releases its proton into the mitochondrial matrix and rotates one step more, eventually creating enough torque (mechanical energy) to rotate 120 degrees (1/3 of a circle) of the y subunit
- the aB subunit is the binding site for ADP and Pi
- The mechanical energy generated by motor rotation is used to produce ATP from the ADP
- the new ATP then falls in the mitochondrial matrix, the empty slot then binds another ADP and Pi
What is the basic overview of what happens in the ETC and OxPHO?
- NADH and FADH2 release high energy electrons
- These create hydrogen ion gradient
- The electrons bind to oxygen
- This produces neg charged oxygen which react with H+ that entered the matrix thro the ATP synthase to produce H20 **most of the oxygen we breathe ends up here and turned into water
- Hydrogen ions also pass thro ATP synthase to produce ATP
How does ADP in the cytosol enter the mitochondria?
It uses ADP/ATP translocases
also known as ADP/ATP carrier protein (AAC) and adenine nucleotide translocases (ANT)
they enable the exchange of cyosolic ADP and mitochondrial ATP across the inner mitochondrial membrane
- *ADP goes from cyoplasm into mitochondrial matrix
- *ATP goes from mitochondrial matrix to cytoplasm
When is the process of ADP/ATP translocase active (also known as ADP/ATP carrier protein (AAC)?
- ADP accumulates in the cytosol
- ATP accumulated in the mitochondria
- H+ concentration is high in the mitochondrial intermembrane space
How does NADH from glycolysis enter the mitochondria?
- The glycerol 3-phosphate shuttle
2. The Malate-Aspartate shuttle
What is the glycerol 3-phosphate shuttle?
Brings NADH into mitochondria
- NADH from glycolysis is used to change DHAP inot glycerol 3-P and gives an NAD+ done by glycerol 3-P dehydrogenase **happens in cytoplasm
- The glycerol 3-P then enters mitochondria where glycerol 3-p dehydrogenase uses an FAD+ to create DHAP and also produces the FADH2
- *problem with is that FADH2 only produces 2 ATPs so its less energy efficient but its faster than the malate-aspartate shuttle
- **the brain uses glycerol 3-P for the speed to get quick energy
What is the malate-aspartate shuttle?
- its used by many tissues, liver, kidney and heart
- NADH from glycolysis is used to reduce oxaloacetate to malate
- The malate is then shuttled thro the inner mitochondrial membrane
- Once there the malate is reoxidized to oxaloacetate, and produces NADH in the process
- This NADH then donates its electrons to the ETC at complex 1, which results with production of 3 ATP
- The oxaloacetate converts to asparate and shuttle out of cytoplasm
What is the big difference in the G 3-P shuttle and the Malate-Aspartate shuttle in term of speed?
The G 3-P is much faster than the MAS but it is not as efficient in terms of how much ATP i makes. The brain uses the G 3-P for the quick access to ATP
What are the consequences of blocking the ETC?
- Less protons will be pumped
- Less ATP ill be produced by ATP synthase-due to less protons
- Demand of oxygen will be down - due to lack of electrons
- NADH and FADH2 will accumulate
- Energy producing metabolic pathways will halt
How do Amytal and Rotenone block the ETC?
They are barbiturates
They block the ETC between NADH dehydrogenase (complex 1) and CoQ
**this privents the utilization of NADHh as a substrate
How does antimycin A block the ETC?
An antibiotic used in a piscicide
It interferes with the electron flow from complex 3 to complex 4
How does cyanide intoxication block the ETC?
It binds the Fe+++ in the heme group of cytochrome C, this results in a complete shit off of the electron flow of the ETC and you die very quickly
How do azides block the ETC?
They work also by inhibiting cytochrome C.
**these are found in gas-producing material in air bags, chemical preservatives
What are posions of respiration uncouplers?
They uncouple the ETC and Proton gradient
They cause protons to leak to the matrix without passing thro the ATP synthase pore
When high energy proton enters mitochondrial matrix thro leaky membrane, extra energy of proton converts to heat
**uncouples the ATP synthase from the ETC
What are the two types of uncouplers?
- natural uncoupler
* **Thermogenin: responsible for producing body heat - Chemical uncoupler
* **Lipid-soluble compounds that shuttle protons across the inner mitochondrial membrane, they generate heat but are not natural and can cause death
What is DNP (2,4- dinitrophenol)
Chemical uncoupler
A precursor for explosives and dyes, banned weight loss diet aid
What is Pentachlorophenol (PCP)
Chemical uncoupler
Used in herbicide, insecticide and an ingredient in antifouling paint
What is an agent that inhibits the ATP synthase?
Oligomycin
Blocks ATP synthase by binding to one of the protein subunits strongly
How does metformin inhibit complex 1?
It blocks pyruvate carboxylase in gluconeogenesis , which has been shown to inhibit mitochondrial respiratory chain at complex 1 without affected any others
**this leads to less ATP, which signals for low energy state- AMPK is activated - glucose utilizing metabolic pathways upregulate. Known as insulin sensitization
What kind of symptoms do electron transport inhibitors cause?
No major alteration of body temp Respiratory depression (slow or irregular breathing) Ataxia (incoordination) Convulsions Cardiac arrest
What kind of symptoms do uncoupling agents cause?
Elevation of body temp
labored respiration
If death occurs, body temp continues to rise after death and rigor mortis rapidly sets in
What is the major source of body heat?
The electron transport chain due to proton leaking (uncoupling event)
How does heat generation by uncoupled mitochondria work with brown adipose tissue?
The natural uncoupling protein THERMOGENIN is expressed more in the mitochondria of brown fat. This means it promotes nonspecific proton leak in those mitochondrial membranes, this leads to production of body heat
