Bioenergetics and Oxidative Phosphorylation
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93 Terms
Q: What is the overall purpose of cellular respiration?
A: To extract energy from fuels and convert it into ATP, with O₂ as the final electron acceptor and CO₂/H₂O as end products.
Q: What are the major fuel sources for cellular respiration?
A: Carbohydrates, fatty acids, and amino acids.
Q: What is the overall flow of energy in cellular respiration?
Fuel → NADH/FADH₂ → ETC → H⁺ gradient → ATP
Q: What are NADH and FADH₂ doing in cellular respiration?
A: They carry high-energy electrons to the ETC.
Q: What does ATP → ADP + Pi accomplish?
A: Releases energy that the cell uses to perform work.
Q: What are the major compartments of the mitochondrion?
A: Outer membrane, intermembrane space, inner membrane, and matrix.
Q: Where are the ETC complexes located?
A: Inner mitochondrial membrane.
Q: Where is ATP synthase located?
A: Inner mitochondrial membrane, with its catalytic portion facing the matrix.
Q: Where does the TCA cycle occur?
A: Primarily in the mitochondrial matrix.
Q: Where are H⁺ concentrated during oxidative phosphorylation?
A: In the intermembrane space.
Q: Are ETC protons pumped outside of the cell?
A: No. They are pumped from the matrix → intermembrane space, both of which are inside the mitochondrion.
Q: Which ETC complexes pump H⁺ across the inner mitochondrial membrane?
A: Complexes I, III, and IV.
Q: In which direction are H⁺ pumped?
A: Matrix → intermembrane space.
Q: Why is the proton gradient useful?
A: It stores potential energy that is used to make ATP.
Q: Where is H⁺ concentration high vs low?
Intermembrane space = HIGH H⁺
Matrix = LOW H⁺
Q: In which direction do H⁺ naturally want to move?
A: Intermembrane space → matrix, down their electrochemical gradient.
Q: Why can't H⁺ simply cross the inner mitochondrial membrane?
A: The inner membrane is highly impermeable to ions, so H⁺ must pass through ATP synthase or another proton pathway.
Q: What happens when H⁺ flows through ATP synthase?
A: The energy from H⁺ movement drives ADP + Pi → ATP
Q: Where is the ETC located?
A: Inner mitochondrial membrane.
Q: What is the correct order of the major ETC complexes?
I → III → IV for NADH electrons
and
II → III → IV for FADH₂ electrons.
Q: Where does NADH enter the ETC?
A: Complex I.
Q: Where does FADH₂ enter the ETC?
A: Complex II.
Q: Which ETC complexes pump protons?
A: I, III, and IV.
Q: How many H⁺ does each ETC complex pump?
A:
Complex I = 4
Complex II = 0
Complex III = 4
Complex IV = 2
⭐ Memorize: 4–0–4–2
Q: Why doesn't Complex II pump H⁺?
A: It transfers electrons from succinate/FADH₂ to CoQ but does not provide enough energy for proton pumping.
Q: What is Complex I also called?
A: NADH dehydrogenase.
Q: What does Complex I do?
A: Transfers electrons from NADH → CoQ and pumps 4 H⁺.
Q: What is Complex II also called?
A: Succinate dehydrogenase.
Q: Why is Complex II unique?
A: It participates in both the TCA cycle and ETC
Q: What does Complex III do?
A: Transfers electrons from CoQH₂ → cytochrome c and pumps 4 H⁺.
Q: What does Complex IV do?
A: Transfers electrons from cytochrome c → O₂, pumps 2 H⁺, and helps reduce O₂ to H₂O.
Q: What is the final electron acceptor of the ETC?
A: Oxygen (O₂).
Q: What happens to O₂ at Complex IV?
A: O₂ accepts electrons and combines with H⁺ to form H₂O.
Q: Why is oxygen essential for oxidative phosphorylation?
A: Without O₂ as the final electron acceptor, electron flow through the ETC stops.
Q: What are the two major roles of Complex IV?
Pumps 2 H⁺ into the intermembrane space
Uses electrons, O₂, and matrix H⁺ to form H₂O
⭐ Think: Complex IV = proton pump + water maker
Q: Approximately how much ATP is produced per NADH?
A: ~2.5 ATP
Q: Approximately how much ATP is produced per FADH₂?
A: ~1.5 ATP
Q: Why does NADH produce more ATP than FADH₂?
A: NADH enters at Complex I, so its electrons drive proton pumping at I + III + IV. FADH₂ enters at Complex II, bypassing Complex I.
Q: How many H⁺ are pumped per NADH-derived pair of electrons?
A: 10 H⁺
(4 + 4 + 2)
Q: How many H⁺ are pumped per FADH₂-derived pair of electrons?
A: 6 H⁺
(0 + 4 + 2)
Q: Approximately how many H⁺ are required per ATP?
A: ~4 H⁺ per ATP according to the lecture.
Q: What is Complex V?
A: ATP synthase.
Q: What powers ATP synthase?
A: The proton motive force created by the H⁺ gradient
Q: In which direction do H⁺ flow through ATP synthase?
A: Intermembrane space → matrix.
Q: What is the basic mechanism of ATP synthase?
A: H⁺ flows through the F₀ portion, causing rotation/conformational changes in the F₁ portion, which drives ATP synthesis.
Q: What are the two components of the proton motive force?
Chemical gradient = difference in H⁺ concentration
Electrical gradient = difference in charge across the membrane
Q: Where is newly synthesized ATP produced?
A: In the mitochondrial matrix
Q: How does ATP leave the mitochondrial matrix?
A: Through the ATP/ADP translocase
Q: What does the ATP/ADP translocase exchange?
A: ATP out of the matrix ↔ ADP into the matrix
Q: Why does ADP need to enter the mitochondrial matrix
A: ATP synthase needs ADP + Pi to make new ATP
Q: Why does ATP become ADP?
A: The cell uses ATP's energy for cellular work:
ATP → ADP + Pi + energy
The ADP can then return to the mitochondria and be recharged into ATP
Q: Why can't cytosolic NADH directly enter the mitochondrial matrix?
A: NADH itself cannot cross the inner mitochondrial membrane
Q: What are the two major shuttles for cytosolic NADH electrons?
A: Glycerol phosphate shuttle and malate-aspartate shuttle
Q: Which shuttle transfers electrons to mitochondrial NADH?
A: Malate-aspartate shuttle.
Q: Which shuttle transfers electrons to FAD and ultimately Complex II?
A: Glycerol phosphate shuttle.
Q: What is the ATP yield of cytosolic NADH through the malate-aspartate shuttle?
A: ~2.5 ATP.
Q: What is the ATP yield of cytosolic NADH through the glycerol phosphate shuttle?
A: ~1.5 ATP.
Q: Why does the glycerol phosphate shuttle produce less ATP?
A: Its electrons enter the ETC at the FAD/Complex II level, bypassing Complex I.
Q: What does rotenone inhibit?
A: Complex I.
Q: What does Amytal inhibit?
A: Complex I again
Q: What does Antimycin A inhibit?
A: Complex III.
Q: What does cyanide inhibit?
A: Complex IV.
Q: What does azide inhibit?
A: Complex IV. again
Q: What does oligomycin inhibit?
A: ATP synthase (Complex V), specifically its F₀ proton channel.
Q: What do atractyloside and bongkrekic acid inhibit?
A: ATP/ADP translocase.
Q: What happens when an ETC inhibitor blocks electron flow?
↓ Electron transport
↓ Proton pumping
↓ Proton gradient
↓ ATP production
↓ O₂ consumption
Q: What happens to NADH when the ETC is inhibited?
A: NADH accumulates because it cannot be efficiently oxidized back to NAD⁺.
Q: Why can ETC inhibition cause lactic acidosis?
A: Impaired oxidative phosphorylation limits aerobic metabolism and NAD⁺ regeneration, promoting pyruvate → lactate.
Q: What is an uncoupler?
A: A substance that dissipates the proton gradient without directly blocking electron transport.
Q: What happens to ATP with an uncoupler?
A: ↓ ATP
Q: What happens to oxygen consumption with an uncoupler?
A: ↑ O₂ consumption/respiration
Q: What happens to the proton gradient with an uncoupler?
A: ↓ Proton gradient
Q: Why does respiration increase with an uncoupler?
A: The proton gradient is dissipated, reducing the "backpressure" on the ETC, so the ETC speeds up trying to rebuild the gradient.
Q: What is DNP?
A: 2,4-dinitrophenol, a protonophore/uncoupler.
Q: What does DNP do to mitochondria?
A: Carries H⁺ across the inner membrane, collapsing the proton gradient.
Q: What can happen with excessive DNP exposure?
A: ↑ respiration + ↓ ATP + ↑ heat production → potentially severe hyperthermia
Q: What is UCP1?
A: Uncoupling protein 1, also called thermogenin.
Q: Where is UCP1 found?
A: Brown adipose tissue.
Q: What is the purpose of UCP1?
A: Produces heat by allowing H⁺ to return to the matrix without generating ATP
Q: What happens when oligomycin blocks ATP synthase?
A: H⁺ cannot flow through ATP synthase → ATP ↓.
Q: What happens to the proton gradient with oligomycin?
A: ↑ Proton gradient because H⁺ continues to be pumped but cannot efficiently return through ATP synthase.
Q: What happens to respiration with oligomycin?
A: ↓ Respiration/O₂ consumption because the increasingly high proton gradient creates backpressure against further proton pumping.
Q: Why is cyanide rapidly lethal?
A: It inhibits Complex IV, preventing electrons from being transferred to O₂ and stopping oxidative phosphorylation.
Q: What happens to ATP during severe cyanide poisoning?
A: ATP production falls dramatically.
Q: Why does cyanide cause cellular hypoxia even when oxygen is present in the blood?
A: Cells cannot use O₂ because Complex IV is inhibited.
Q: How does nitrite help treat cyanide poisoning?
A: Nitrite converts Fe²⁺ hemoglobin → Fe³⁺ methemoglobin, which binds cyanide and removes it from Complex IV.
Q: How does thiosulfate help treat cyanide poisoning?
A: It provides sulfur for conversion of cyanide → thiocyanate, which is much less toxic and can be excreted.
Q: Compare an ETC inhibitor with an uncoupler.
ETC inhibitor | Uncoupler | |
|---|---|---|
ETC | ↓ | ↑ |
Proton gradient | ↓* | ↓ |
ATP | ↓ | ↓ |
O₂ consumption | ↓ | ↑ |
Heat | May vary | ↑ |
*With direct ETC blockade, proton pumping falls and the gradient eventually decreases.
Q: What pattern suggests oligomycin?
ATP ↓ + respiration ↓ + proton gradient ↑
Q: What pattern suggests an uncoupler such as DNP?
ATP ↓ + respiration ↑ + proton gradient ↓ + heat ↑
Q: What pattern suggests cyanide?
Complex IV blocked → O₂ cannot accept electrons → ETC stops → ATP ↓
Q: What pattern suggests Complex I inhibition?
NADH ↑ + electron flow ↓ + proton pumping ↓ + ATP ↓
⭐ Final "Know This Cold" Deck
ETC location → inner mitochondrial membrane
NADH enters → Complex I
FADH₂ enters → Complex II
Proton pumps → I, III, IV
H⁺ pumping → 4–0–4–2
NADH → 2.5 ATP
FADH₂ → 1.5 ATP
O₂ → final electron acceptor
Complex IV → H₂O formation
H⁺ → intermembrane space → ATP synthase → matrix
ATP synthase → ADP + Pi → ATP
ATP/ADP translocase → ATP out, ADP in
Rotenone/Amytal → Complex I
Antimycin A → Complex III
Cyanide/Azide → Complex IV
Oligomycin → Complex V
Atractyloside/Bongkrekic acid → ATP/ADP translocase
Uncoupler → ATP ↓, O₂ consumption ↑
DNP → uncoupler
UCP1 → brown fat → heat
Oligomycin → ATP ↓, respiration ↓, gradient ↑
Cyanide → Complex IV → cannot use O₂
Malate-aspartate shuttle → ~2.5 ATP
Glycerol phosphate shuttle → ~1.5 ATP
ETC inhibition → NADH accumulates