Ch 15 Electron Transport Chain Flashcards
What is the overall equation for aerobic respiration?
6O2 + C6H12O6 → 6H2O + 6CO2 + energy (ATP)
This equation summarizes the process of aerobic respiration, where glucose is oxidized to produce water, carbon dioxide, and ATP.
What is oxidative phosphorylation?
The process by which ATP is formed as a result of electrons being transferred from NADH or FADH2 to O2 by a series of electron carriers
This process occurs in the mitochondria and is a key component of cellular respiration.
What does electron transport drive in mitochondria?
The pumping of protons across the inner membrane to the intermembrane space
This creates a proton gradient that is essential for ATP synthesis.
What is the purpose of the electron transport chain?
To transport protons (H+) from the matrix across the inner membrane of the mitochondria
This results in a higher concentration of protons in the intermembrane space.
What is a proton gradient also known as?
Chemiosmosis
This refers to the movement of protons across a membrane, leading to ATP production.
What is the role of the proton gradient in ATP synthesis?
It provides the energy for phosphorylating ADP to ATP
This process occurs through ATP synthase.
What is reduction potential?
The tendency of a substance to accept electrons (to become reduced)
It is described by its standard reduction potential (εo′).
What is the reference point for reduction potentials?
The hydrogen electrode
This half-cell is considered to have a voltage of zero.
What are the components of the Nernst equation?
R, T, n, and ℱ
R is the gas constant, T is temperature in Kelvin, n is the number of electrons, and ℱ is Faraday’s constant.
What is the result of the directional flow of electrons in the electron transport chain?
It involves a series of oxidation-reduction reactions
This flow is determined by the reduction potentials of the electron carriers.
What does the term ‘oxidation’ refer to?
Loss of electrons or hydrogen
This is part of the redox reactions occurring in the electron transport chain.
What does the term ‘reduction’ refer to?
Gain of electrons or hydrogen
This is the opposite of oxidation in redox reactions.
What is the function of Complex I in the electron transport chain?
Transfers electrons from NADH to ubiquinone
Complex I is the largest electron transport protein in the mitochondrial respiratory chain.
What is the significance of flavin mononucleotide (FMN) in Complex I?
It picks up two electrons donated by NADH and transfers them to iron-sulfur clusters
FMN is a noncovalently bound prosthetic group.
What is the result of the reduction of iron in iron-sulfur clusters?
Iron is reduced to Fe2+ when it gains an electron and oxidized to Fe3+ when it loses an electron
This process facilitates the transfer of electrons through the electron transport chain.
What does the electron transport chain act like?
A battery that charges the mitochondrial inner membrane
This charging occurs through the movement of electrons and protons.
How many protons does Complex I transfer from the matrix to the intermembrane space?
Four protons
This active transport is driven by electron transfer.
What is the primary role of coenzyme Q (ubiquinone) in the electron transport chain?
Acts as an electron carrier that accepts electrons from Complex I and Complex II
Ubiquinone is crucial for the continuation of the electron transport chain.
What is the significance of the directional flow of electrons in the electron transport chain?
Electrons travel from one redox center to another of increasing reduction potential
This gradient is essential for ATP synthesis.
Fill in the blank: The tendency of a substance to accept electrons is described by its _______.
standard reduction potential
This concept is fundamental in understanding redox reactions.
True or False: Electrons usually travel in pairs in biological systems.
True
However, they may also be transferred one at a time.
What is the oxidized form of Coenzyme Q called?
Ubiquinone
Coenzyme Q is referred to as ubiquinone when it is in its oxidized state.
What is the reduced form of Coenzyme Q called?
Ubiquinol
Coenzyme Q becomes ubiquinol when it is reduced.
What type of reaction occurs at Complex I involving NADH?
Oxidation and reduction
NADH is oxidized, and Coenzyme Q is reduced in this reaction.
What is the overall reaction of Complex I?
Transfer of electrons from NADH to Coenzyme Q
This process is exergonic and drives ADP phosphorylation.
Which cycle contributes to the ubiquinol pool?
The TCA cycle
Specifically, the reaction catalyzed by complex II (succinate dehydrogenase) contributes to the pool.
What does Complex III do?
Transfers electrons from ubiquinol to cytochrome c and pumps protons
This process helps in creating a proton gradient across the membrane.
What is the Q cycle?
The route of electrons from ubiquinol to cytochrome c
It involves two rounds of electron transfer and translocates protons.
What is cytochrome c’s role?
Transfers electrons between Complexes III and IV
It carries electrons one at a time to aid in the reduction of oxygen.
What is consumed in the reduction of molecular oxygen to water?
Four electrons from cytochrome c
This process occurs at Complex IV.
What is an anaplerotic reaction?
A reaction that replenishes citric acid cycle intermediates
An example is the conversion of pyruvate to oxaloacetate.
Which of the following is NOT true of glycerol phospholipids?
They are also called sphingolipids
Sphingolipids do not have a glycerol backbone; they are based on sphingosine.
Which fatty acid is considered an ω-3 fatty acid?
Eicosapentaenoic acid (EPA)
EPA is 20:5 Δ5,8,11,14,17 and is listed on many food labels.
Any sugar that has a free aldehyde group is called a(n) _______.
Reducing sugar
The presence of a free aldehyde makes the sugar capable of reducing other compounds.
Which enzyme is not required for the synthesis of branched glycogen?
Glycogen phosphorylase
Glycogen phosphorylase is involved in glycogen breakdown, not synthesis.
What makes the reaction catalyzed by citrate synthase highly exergonic?
Hydrolysis of thioester
The departure of CoA during the reaction makes it energetically favorable.
What bond does citrate synthase synthesize?
C—C bond
Citrate synthase can form this bond without a metal ion cofactor.
What do cytochromes contain?
Heme prosthetic groups
These groups undergo reversible one-electron reduction.
What is the role of iron-sulfur clusters?
To facilitate electron transfer
Electrons are passed to these clusters during the electron transport chain.
What is the standard reduction potential of NAD+?
-0.315 V
This value is used in calculations involving electron transport and energy changes in biochemical reactions.
What is the formula to calculate ΔG°’ for electron transport reactions?
ΔG°’ = -2 ∙ 96,485 J/V/mol ∙ [E°’final - E°’initial]
This formula relates standard reduction potentials to free energy changes.
What is the ΔG°’ value for the half-reaction of NAD+ to NADH?
-218 kJ/mol
This value indicates the energy available from the reduction of NAD+ to NADH.
What does Complex IV of the electron transport chain contain?
Two cytochromes a, a3 and two copper atoms
These components are involved in the transfer of electrons to oxygen.
What is the role of coenzyme Q in the electron transport chain?
Transfers electrons from Complex I to Complex III
Coenzyme Q is also known as ubiquinone when oxidized and ubiquinol when reduced.
What is chemiosmosis?
The process by which the protonmotive force links electron transport to ATP synthesis
It involves the generation of a proton gradient across the mitochondrial membrane.
What is the ΔG°’ value for Complex I (NADH to QH2)?
-69.5 kJ/mol
This value represents the energy released during the electron transfer at Complex I.
What is the ΔG°’ value for Complex III (QH2 to cytochrome c)?
-36.7 kJ/mol
This indicates the energy change associated with electron transport at Complex III.
What is the ΔG°’ value for Complex IV (cytochrome c to O2)?
-112.0 kJ/mol
This value reflects the energy released during the final step of electron transport.
What is the total ΔG°’ for the complete process from NADH to O2?
-218.2 kJ/mol
This value indicates the overall energy change for the oxidation of NADH to O2.
What does the protonmotive force consist of?
- Electrical potential energy
- Chemical potential energy
Together, these form the electrochemical gradient that drives ATP synthesis.
What is ATP synthase also known as?
F0-F1 complex
It functions to synthesize ATP using the proton gradient generated by electron transport.
Who proposed the Chemiosmotic Hypothesis?
Peter Mitchell
He was awarded the Nobel Prize in Chemistry in 1978 for this work.
What is the role of the F0 component of ATP synthase?
Functions as a transmembrane channel for H+
It allows protons to flow back into the mitochondrial matrix.
What does the F1 component of ATP synthase do?
Catalyzes the reaction ADP + Pi → ATP + H2O
This component is responsible for the actual synthesis of ATP.
What are the three conformational states of the β subunits in ATP synthase?
- Open (O)
- Loose-binding (L)
- Tight-binding (T)
These states correspond to different binding affinities for adenine nucleotides.
What is the significance of the c ring in ATP synthase?
It rotates to facilitate proton transport and ATP synthesis
The rotation is driven by the flow of protons through the F0 component.
What experimental evidence supports the rotation of ATP synthase?
Rotation of the c ring observed in E. coli F1F0-ATPase
This was demonstrated by Noji et al. in 1997.
What is the role of the binding change mechanism in ATP synthase?
Links proton gradient changes to ATP synthesis
It allows for the conversion of mechanical energy from rotation into chemical energy in the form of ATP.
What happens to the protonated c subunit in ATP synthase?
It moves away and rotates the c ring
This movement brings another c subunit into position to release its bound proton into the matrix.
What leads to changes in conformation in ATP synthase?
The proton gradient
How many sites for substrate are on ATP synthase?
3 sites
What are the three possible conformations of ATP synthase?
- Open (O)
- Loose-binding (L)
- Tight-binding (T)
What is the affinity of the Open (O) conformation for substrate?
Low affinity
What does the Loose-binding (L) conformation do?
Loosely binds ADP and Pi
What is the function of the Tight-binding (T) conformation?
Catalytically active, binds ATP
What causes the rotation of the sites in ATP synthase?
Proton flux through ATP synthase
What does proton flux convert Loose-binding (L) to?
Tight-binding (T)
What does proton flux convert Tight-binding (T) to?
Open (O)
What is the P/O ratio when NADH is oxidized?
2.5
What is the P/O ratio when FADH2 is oxidized?
1.5
Why is there a difference in P/O ratios between NADH and FADH2?
The oxidation of NADH exports more protons from the matrix than FADH2
What is the upper limit of ATP produced per NADH oxidized?
3.7 ATP per NADH
What reduces the maximum ATP yield from NADH to 2.5 ATP?
H+ leaks in the membrane
What is the maximum ATP yield from FADH2?
2.2 ATP per FADH2
What reduces the maximum ATP yield from FADH2 to 1.5 ATP?
H+ leaks
What is produced from the complete oxidation of one glucose molecule?
6CO2 + 6H2O + energy (ATP)
What is the total ATP yield from one glucose molecule via the glycerol-phosphate shuttle?
30 ATP
What is the total ATP yield from one glucose molecule via the malate-aspartate shuttle?
32 ATP
What are uncouplers?
Hydrophobic molecules with a dissociable proton that inhibit ATP production without inhibiting electron transport
Give an example of an uncoupler.
2,4-dinitrophenol
What is the role of thermogenin (UCP-1)?
Dissipates the proton gradient producing heat instead of ATP
What regulates ATP synthase in eukaryotes?
Inhibitory factor 1 (IF1)
What happens to IF1 when the pH drops?
IF1 dimerizes and prevents ATP synthase from functioning
Name one respiratory inhibitor.
Carbon monoxide
Which complex does cyanide inhibit?
Complex IV
What was the purpose of the uncoupler 2,4-Dinitrophenol historically?
Used in diet pills to burn fat
