bioch lec 8- oxidative phosphorylation
What are the two major purposes of catabolic pathways? (2 purposes)
They break down large molecules into smaller ones and release/store energy in high-energy molecules (ATP, NADH, FADH₂).
What makes catabolic pathways oxidative? (1 reason)
Metabolites are oxidized while cofactors like NAD⁺/FAD are reduced, and later re-oxidized to generate ATP.
What are the two linked processes in oxidative phosphorylation? (2 processes)
(1) Re-oxidation of NADH/FADH₂ with reduction of O₂ → H₂O, and
(2) Phosphorylation of ADP → ATP, linked by a proton gradient.
Write the half-reactions for NADH and FADH₂ oxidation. (2 reactions)
NADH → NAD⁺ + H⁺ + 2e⁻
FADH₂ → FAD + 2H⁺ + 2e⁻
What reaction shows O₂ as the terminal electron acceptor? (1 reaction)
½ O₂ + 2H⁺ + 2e⁻ → H₂O (or full form 4H⁺ + 4e⁻ + O₂ → 2H₂O).
Where are oxidative phosphorylation proteins located? (1 location)
They are embedded in the inner mitochondrial membrane.
What are the four major ETC components? (4 items)
Complexes I–IV, Coenzyme Q, and Cytochrome c. Q is lipid-soluble; Cyt c is peripheral and mobile
What are the five cofactors involved in electron transport? (5 items)
FMN, Fe-S clusters, Cu²⁺, cytochrome heme groups, and Coenzyme Q.
What determines the direction of electron flow? (1 principle)
Electrons move from lower to higher reduction potential cofactors.
What is the relationship between ΔE°′ and ΔG°′? (1 equation)
ΔG°′ = −nFΔE°′; higher ΔE°′ → more negative ΔG°′.
What does FMN do in Complex I? (1 role)
FMN accepts 2 electrons + 2H⁺ to become FMNH₂, analogous to FAD but without adenosine
What functional role do Fe–S clusters play? (1 function)
They cycle between Fe³⁺ and Fe²⁺ to transfer single electrons.
How do cytochromes differ from hemoglobin/myoglobin heme? (1 distinction)
Cytochrome hemes switch oxidation states (Fe³⁺/Fe²⁺) in electron transport.
What is the role of Coenzyme Q? (2 roles)
It is a lipid-soluble carrier that accepts 2 e⁻ + 2H⁺ (Q → QH₂) and transfers electrons from Complexes I/II to III.
Which complexes pump protons and how many per NADH? (3 complexes)
Complexes I, III, and IV pump protons; total 10 H⁺ moved per NADH oxidized. Complex II does not pump protons.
What reaction gives Complex II its identity? (1 reaction)
It catalyzes succinate → fumarate, transferring electrons to Q without pumping protons.
How many protons are pumped per FADH₂ oxidation? (1 number)
6 H⁺ are moved per FADH₂ oxidized.
Why does FADH₂ yield fewer protons/ATP than NADH? (1 reason)
Because FADH₂ donates electrons directly to Complex II, bypassing Complex I (a proton-pumping site).
What two components make up the proton electrochemical gradient? (2 components)
A pH gradient (ΔpH) and a charge gradient (ΔΨ). The matrix is negative/high pH; IMS is positive/low pH.
What is the function of the proton gradient in oxidative phosphorylation? (1 function)
It converts potential energy into ATP via ATP synthase.
What is the estimated number of protons needed to make one ATP? (1 number)
Approximately 3 H⁺ per ATP synthesized.
Based on proton pumping alone, how many ATP are made per NADH? (1 number)
Roughly 10 H⁺ ÷ 3 H⁺ ≈ 3 ATP per NADH. (Approximation used for conceptual understanding.)
What are the two major structural portions of ATP synthase? (2 portions)
F₀ (transmembrane H⁺ channel) and F₁ (catalytic ATP-forming portion).
What triggers ATP synthesis mechanistically? (1 event)
Proton flow through F₀ drives rotation of the central shaft, causing conformational changes in F₁ that catalyze ADP + Pi → ATP.
How many ATP are produced per full rotation of ATP synthase? (1 number)
A full turn generates 3 ATP from its three active catalytic sites.
What is the role of the adenine nucleotide translocase? (1 role)
It exchanges ATP out of the matrix for ADP in, enabling ATP use in the cytosol.
What does the Pi–H⁺ symporter do? (1 function)
It imports Pi + H⁺ into the matrix for ATP synthesis.
Why are oxidation and phosphorylation described as “coupled”? (1 explanation)
Electron transport, NADH re-oxidation, and O₂ consumption all depend on ATP synthase activity via the proton gradient magnitude.
How does ADP concentration affect O₂ consumption? (1 relationship)
When ADP rises, ATP synthase activity increases → proton gradient decreases → electron transport accelerates → O₂ consumption increases.
What does the P:O ratio measure? (1 definition)
The number of ATP molecules produced per oxygen atom reduced to water.
What are the P:O ratios for NADH and FADH₂? (2 numbers)
Approximately 2.5 for NADH and 1.5 for FADH₂ (non-stoichiometric averages).
Why does P:O vary? (1 reason)
Uncoupling or variable proton leak alters how many H⁺ contribute to ATP synthesis.
What happens during low energy demand? (5 effects)
Low ADP/Pi → low ATP synthase → ↑H⁺ gradient → ↓electron transport → ↓O₂ use → ↑NADH/FADH₂ → inhibition of CAC/PDH.
What happens during high energy demand? (5 effects)
High ADP/Pi → ↑ATP synthase → ↓H⁺ gradient → ↑electron transport → ↑O₂ use → ↓NADH/FADH₂ → activation of CAC/PDH.
What does uncoupling do to oxygen consumption? (1 effect)
It allows protons to enter the matrix without ATP synthesis, so electron transport speeds up and O₂ use increases.
What is an uncoupling protein (UCP)? (1 definition)
A membrane protein that allows proton re-entry into the matrix without ATP synthesis, generating heat.
What happens to electron transport during uncoupling? (1 effect)
Electron transport accelerates because the proton gradient is dissipated rapidly.
What metabolic consequences follow uncoupling? (2 consequences)
Increased fuel oxidation and increased O₂ consumption (but no ATP production)
Why is 2,4-dinitrophenol dangerous? (1 reason)
It is a chemical uncoupler that collapses the proton gradient, causing excess heat production and potentially fatal hyperthermia.