Electron Transport Chain Flashcards
The total process of oxidizing glucose, how many ATPs, NADHs, FADH2s are made?
How many ATP is made from substrate-level phosphorylation
How many ATP is made from oxidative phosphorylation?
From Glucose -> 2 Pyruvae: 2 ATPs and 2 NADHs
From 2 pyruvate -> 2 Acetyl CoAs: 2 NADHs
From 2 Acetyl CoAs in the TCA cycle: 6 NADHs, 2 FADH2, 2 ATP
4 ATP is made from substrate level phosphoryl;ation
What is oxidative phosphorylation?
It includes the electron transport chain and ATP synthesis.
It captures energy of high-energy electrons to synthesize ATP.
Electrons go from NADH and FADH2 to O2 in the electron transprot chain (ETC)
Flows of electrons crate a proton gradient that ise used to power the synthesis of ATP
Why was there so much opposition against the chemiosmotic theory?
What is the chemiosmotic theory?
Others thought that oxidative phosphorylation must involve an intermediate with a high-energy chemical bond (substrate lelvel phosphorylation)
But mitchel proposed that a proton gradient across the inner mt membrane provided the energy for ATP synthesis
What is the structure of the mitochondria?
Matrix space, inner mt membrane, intermembrane space, outer mt membrane
What is the artificial system used for testing the ETC made of?
- A membrane
- A bacterial proton pump activated by light (called bacteriorhodopsin)
- ATP synthase
How does the artificial system used for testing the ETC work>
In the presence of light, the bacteriorhodopsoin protein pumps protons into the vesicle interior.
Directional pumping results in:
- Chemical gradient across the membrane
- electrical gradient due to separation of charge
When protons flow down the electrochemical gradients through ATP synthase, they generate ATP on the outside
What are some experimental evidence about the concentration of protons in the artificial experiment
the concentration of protons in the external medium and the amount of ATP produced in the presence and absence of light was measured
What can you conclude from the artificial system?
In the presence of light, the proton pump is activated and the protons are pumped to one side of the membrane, leading to formation of a proton gradient.
The proton gradient, in turn, powered synthesis of ATP via ATP synthase.
No need for high energy chemical intermediate
What would happen if researchers added a transmembrane protein channel that allowed protons to freely pass through it?
Less ATP would be produced when the light is on because protons would bypass the ATP synthase
What is oxidative phosphorylation
Electron transport chain + ATP synthesis
Give an executive summary of the electron transport chain (ETC)
They are combined redox reactions that occur sequentially in protein complexes in the inner mitochondrial membrane.
Protein complexes use energy released by electron flow to pump H+ into the intermembrane space
In which part of the mitochondria is ATP generated
the matrix
What is cellular respiration
Generation of high-transfer potential electrons by the TCA cycle, their flow through the respiratory chain and synthesis of ATP
Where does the citric acid cycle and fatty acid oxidation occur?
In the matrix
Describe the outer mitochondrial membrnae
Its permeable to most small ions and molecules because of the channel protein mitochondrial porin (not selective)
Describe the inner mitochondrial membrane
The inner membrane, which is folded into ridges is called cristae, is impermeable to most molecules. Transporters shuttle metabolites across inner membrane (requiring transporters)
What is the inner membrane the site for
It is the site of eletron transport and ATP synthesis
What is electron-transfer potential (E0’)
electron transfer potential of NADH and FADH2 will be converted into phosphoryl-transfer potential of ATP. E0’ is the experession for electron transfer potential.
Redox potential is the measure of a molecules’ tendency to donate or accept electrons
A strong ___ agent readily ___ electrons and has a ____ E0’. Example: NADH and FADH2
reducing
donates
Negative E0’
Ex.NADH FADH2
A strong ___ agent readily ___ electrons and has a ____ E0’. Example: O2
Oxidiizing agent
accepts
A strong reducing agent has a ___ affinity for electrons than does H2
lower
A strong oxidizing agent has a ___ affinity for electrons than H2
higher
The ultimate electron acceptor is Oxygen, what happens in anaerobic ocnditions
Sulfur, Iron replaces instead
What are the 4 complexes of the electron transport chain?
I. NADH - Q oxidoreductase
II. Succinate-Q reductase
III. Q-cytochrome c oxidoreductase
IV. Cytochrome C oxidase
What is a respirasome?
The 4 complexes of the electron transport chain associated togehter.
This facilitates the rapid transfer of substrate and prevents the release of reaction intermediates.
From NADH to O2, these translocation of electrons are needed
I. NADH-Q oxidoreductase
III. Q-cytochrome c oxidoreductase
IV. Cytochrome C oxidase
From FADH2 to to O2, these translocation of electrons are needed
II. Succinate-Q reductase
III. Q-cytochrome c oxidoreductase
IV. Cytochrome C oxidase
ubiquinone Q
What electron carriers ferry electrons from one complex to the nex
Coenzyme Q shuttles electrons from I to III (e comes from NADH)
Coenzyme Q shuttles electrons from II to III (e came from FADH2)
Cytochrome C shuttles electrons from III to IV (e came from NADH or FADH2)
What is the ordeer of the intermediate electron carriers
I, Q - II, III, c, IV
electron affinity increases as the electrons move down the chain
starts with negative, and ends with positive.
The redox potential increases (reduction potential)
Oxidation of NADH+H starting with complex I (I,III,IV) leads to translocation of how many H?
10 H+
Oxidation of NADH+H starting with complex II (II,III,IV) leads to translocation of how many H?
translocation of 6H+
How many electrons are transported at a time by Complex I
2 electrons at a time
How many electrons are transported at a time by Complex II
2 electrons at a time
How many electrons are transported at a time by Complex III
1 at a time
How many electrons are transported at a time by Complex IV
1 at a time
How many electrons are transported at a time by Ubiquinone, coenzyme Q?
receives 2 electrons, but passes 1 at a time
What are the prosthetic groups of complex I
FMN Fe-S
What are the prosthetic groups of complex II
FAD, Fe-S
What are the prosthetic groups of complex III
Hemme, FeS
What are the prosthetic groups of complex IV
Hemme, Cu
Where is the positive side?
The intermembrane space
Where is the negative side?
The mitochondrial matrix
ETC topology: complexes I, III and IV
tranverse the inner mt membrane and translocate protons across
ETC topology: coenzyme Q
Diffuses laterally within the membrane to donate electorns to III
ETC topoplogy: cytochrome C
Cytochrome C associates with the cytosolic side of the membrnae and carries electrons from III to IV
How many electrons do Q and cyt C transport at a time? how many trips are required
Q and cyt c transport 1 electron at a time. 2 trips are required to transfer a pair of electrons from NADH and FADH2
Elaborate on Complex I from NADH to Ubiquinone
- Oxidation of NADH in the matrix releases 2 electrons (2 e at a time) and is transferred to FMN
- Electrons are transfered from one carrier to another (fe-S cluster)
- Electrons are dononated to ubiquione
Q (ubiquinone) -> QH2 (ubiquinol)
What is the reduce version of Q called? Whats required to reduce Q to QH2
QH2 ubiquinol?
2 electrons and 2 H+ are used to reduce Q to QH2
What is the overall formula from NADH to Ubiquinone
NADH + H+
+ Q
+ 4H+ (matrix)
->
NAD+
+ QH2
+ 4H+ (intermmebrnae)
How does complex I work as a proton pump
A site near the top captures NADH. Complex I strips the electrons from these hydrogens using a FMN cofactor
Electrons are shipped down a chain of Fe-Sulfur clusters. This process generates energy.
Each pair of electrons from NADH will power the transport of 4 protons. Each of these protons is transported by a dedicated protein pump.
What is FMN?
Flavin mononucleotide
What is a prosthetic group?
Prosthetic groups are non-peptide (non-protein) compounds that mostly attach to proteins
Is Ubiquinone Q a protein
No, not a protein. Its a metabolite.
Elaborate on Complex II: from FADH2 to ubiquinone
In TCA, oxidation of succinate to fumarate transfers a pair of electrons (2e at a time) to FAD.
Succinate dehydrogenase is membrane-bound.
Oxidation of FADH2 within complex II transfers electrons through a series of Fe-S clusters at cytochrome b560. => transfered to Q
In the final redox reaction, 2 electrons + 2 H+ are used to reduce Q to QH2. No protons are translocated by complex II.
What does the Q cycle do?
Converts a 2 electron transport system into a 1 electron transport system in complex III
What are the different oxidation states of ubiquinone
Oxidized (2 ketone groups - ubiquinone)
Semiquinone
Reduced (uniquinol - 2 hydroxy groups)
What is Coenzyme Q, Q10, ubiquinone
It is a mobile electron carrier that transpports electrons laterally from complex I or II to II.
Can receive 2 electrons and pass 1 electron at a time to the mobile carrier cytochrome C
Elaborate on complex III
QH2 passes 2 electrons to complex III, but the acceptor of electrons in this complex (cyt C) can only acccept 1 electron. The 2 binding sites for Q in complex III converts the 2 electrons into a one-electron transport
How does the Q cycle run within complex III? (6 steps)
- Complex III accepts 2 electrons from QH2 from membrnae. QH2 binds to 1 of the 2 sites in complex III.
- One electron is passed to cyt C. Moves away to comlex 4.
- The other electron is taken by Q bound at the other biniding site -> become semiquinone
- the newly formed.Q dissociates and enters into the Q pool.
- A second QH2 donates 2 electrons. One to cty c, the other to semiquinone bound at the second site. (Q is formed -> return to Q poool)
- Second electron transfer to semiquinone results in uptake from 2 protons from the matrix to form QH2
Summarize the Q cycle
2 binding sites: Q0 and Qi
4 protons are released into the intermembrane space
2 protons are removed from the mitochondrial matrix and passed to cyt C
Are any protons removed from the mitochondrial matrix during the Q cycle
2 protons
Elaboraate on cytochrome C
Slides along the cytosolic side of the mitochondrial inner membrane, delivering electrons from complex III to IV.
Contains a heme group, transports 1 electron at a time.
the 3D structure of cytochrome C is conserved among distantly related species.
Cytochrome C is a soluable, monomeric protein
First half of the Q cycle pumps…electrons
Second half of the Q cycle pumps..
2H+
2H+
Elaborate on Complex IV from cytochrome C
- Accepts electrons (one at a time) from Cyt C and donates them to oxygen to form water
A total of four H+ are involved in complex IV reactions
Four next H+ are translocated across the membrane contributing to the gradeint
Four H+ are used to form 2H2O
How many electrons are required to reduce each molecule of O2
Four electrons are required to reduce each molecule of O , and two water molecules are formed in the process.
Which chemicals inhibit complex I
Metformin
Phenformin
Rotenone
IM156
Which chemicals inhbit complex II
3-NPA
Malonate
TTFA
Atpenin A5
Lonidamine
Which chemicals inhibit complex III
Antimycin A
Which chemicals inhibit complex IV
Cyanide
Which chemicals inhibit ATP synthase
Oligomycin
GBOXIN
Which chemicals inhbit the formation of NADH
Gossypol
What are some dangerous side reactions of the reductin of O2
normal conditions: Transfer of 4 electrons lead to 2 H2O molecules
Abnormal conditions: partial reduction of O2 generates hazardous cmpounds
Transfer of a single electron to O2 forms superoxide ion
transfer of 2 electrons yields peroxide
ROS can react with macromolecules to cause oxidative damange
Are ROS completely harmful
They are known hazards, however, their controlled genration is important for signal transduction pathways. The dual roles of ROS are an excellent example of the complexity of metabolism.
How do defend from ROS?
Using non-enzymatic antioxidants such as vitamin C, E, beta carotente
or antioxidant enzymes :
superoxide dismutase (SOD)
catalase (CAT)
glutathione peroxidase (GPx_
Inhibitors or uncouplers can disrupt the ETC which leads to
reduction of ATP synthesized
What does Rotenone do? How is it applied
Its a strong inhibitor of complex I.
Doesnt have a long life span.
Incomplete electron transfer leads to ATP depletion -> oxidative stress
Rotenone has been proposed as a target for cancer therapry for tumors relying on oxidative metabolism (the few cancers that use oxidative metabolism)
What is the effect of rotenone on the citric acid cycle
Result of exploiting inhibitors of ETC as anticenter drugs
Induced lack of energy, but widespresd effets on heart and bones -> not safe as a anticancer drug
What is noncoupling proteins
non coupling proteins are mitochondrial carrier proteins which are able to dissipate the proton gradient of the inner mitochondrial membrane.
How has mistletoe lost most of its respiratory capacity (viscum album)
Lacks activity of mitochondrial complex I.
II-V are decreased in abundance.
Alternative NADH dehydrogenases and the alternative oxidases are increased,
Decreased mitochondrial ATP production is complensaed by increase glycolytic flow.
Mistle takes eerngy from host plants
