L32: Oxidative Phosphorylation Flashcards
Where does oxidative phosphorylation take place?
In the mitochondria
What is oxidative phosphorylation?
The process in which ATP is formed as a result of the transfer of electrons from NADH or FADH2 to O2 by a series of electron carriers
In oxidative phosphorylation, what happens when oxygen accepts electrons from NADH and FADH2?
Oxygen is reduced to water
Why is the inner mitcohondrial membrane convulated>?
The inner membrane’s folds (cristae) increase the surface area, facilitating the high concentration of embedded proteins necessary for electron transport.
How are NADH and FADH2 brought into the mitochonria?
Via shuttles
Is it true that the inner mitochondrial membrane is impermeable to NADH?
Yes
Why doesn’t cytosolic NADH (i.e. from glycolysis) get into the matrix?
It doesn’t, because the inner mitochondrial membrane is impermeable to NADH. But electrons from NADH enter the mitochondrial matrix
Which 2 shuttles transport electrons from NADH across the mitochondrial membranes?
glycerol phosphate shuttle
malate shuttle
Is oxidative phosphorylation aerobic or anaerobic?
Aerbic, and it stops without the presence of oxygen
What is the purpose of oxidative phosphorylation?
To harvest energy from NADH and FADH2 to produce ATP.
what is the mitochondrial matrix the site of?
the citric acid cycle
What does the citric acid cycle produce?
Acetyl-CoA oxidation produces 6 NADH, 2 FADH2, and 2 GTP.
Describe the glycerol phosphate shuttle
- Cytoplasmic NADH reduces dihydroxyacetone phosphate (DHAP) to glycerol-3-phosphate (G3P).
- G3P enters the mitochondria and is oxidized back to DHAP by mitochondrial glycerol-3-phosphate dehydrogenase, transferring electrons to FAD, forming FADH2.
- FADH2 enters the ETC at ubiquinone (Complex III), bypassing Complex I.
- Efficiency Loss: Produces ~1.5 ATP per NADH instead of 2.5 ATp, as only 6H+ pumped instead of 10.
Describe the malate shuffle
When is the malate shuffle used?
In organs like the heart and liver, where energy(ATP) must be conserved
Describe the malate shuttle
- Used in heart and liver
- A complex redox shuttle. The process involves transferring electrons via malate, oxaloacetate, aspartate, and other intermediates in a cycle.
- Net reaction is NADH moved to
mitochondria - Produces more ATP than the other shuttle
- It avoids energy loss associated with bypassing Complex I in the electron transport chain (ETC).
How does ADP and Pi get into the matrix and how does ATP get into the cytosol?
Using antiporters
Moevement in ETC when you start with NADH
NADH➞ cpx I ➞ cpx III ➞ cpx IV ➞ O2
Moevement in ETC when you start with FADH2
FADH2➞ cpx II ➞ cpx III ➞ cpx IV ➞ O2
Are the respiratory complexes just different parts of the electron transport chain?
Yes
Do the complexes themselves make ATP?
No, they facilitate the necessary energy for the production of ATP by pumping protons into the inter-membrane space. ATP synthase tehn uses this proton gradient to synthesise ATP.
ETC in terms of energetics
- Moving from lower to higher redox potentials.
- More free energy is released as you move across theETC
Describe complex I
- The first protein complex of the ETC.
- NADH is oxidised to NAD+ and the electrons from this are transferred to ubiquinone (Q).
- The redox potential is becoming more positive i.e., ∆E is positive . So ∆G is negative (free energy is released).
- The overall result is that 4 protons pumped across membrane
What prosthetic groups are involved in electron transport in complex I?
Flavin
Iron sulfur Clusters (very good at carrying electrons + have quite low redox potentials0
Describe complex III
- Includes iron sulfur complexes and cytochromes. (cytochromes have highe redox potential, allow for release of free energy).
- Ubiquinone to deleivers electorns to Cytochrome C. Cytochrome C can only carry one electron at a time due to its Heme (iron) group
- Relay of 2 electron (from ubiquinone) to 1 electron carrier called Q cycle
- 4 protons are pumped across the membrane overall (2 from complex itself, and 2 from the Q cycle)
Q cycle
- Ubiquinone becomes fully oxidised
- Ubiquinone delivers its electrons to complex 3 and 2 protons go across the membrane.
- One electron gets ferried on to cytochrome C and cytochrome C can then leave.
- The other electron then goes to a semi-quinone
- a new ubiqunnone will then come in with more electrons
- one electron will be carried off by cytochrome C.
- The other electron will then go down and reduce the semi quinone to a fully reduced form of quinone.
- That quinone will then leave back out to the membrane and get rid of its electrons
Describe Complex IV
- Also consists of cytochromes and cupper
- Cytochrome C delivers electrons to Oxygen.
- Oxygen is the final electron acceptor will be reduced to water.
- Free energy will be released.
- Result: 2 protons pumped across membrane
- Oxygen reduction is tightly controlled because the intermediates (e.g., superoxide, peroxide) are highly reactive and damaging if they escape.
Describe complex II
- Complex II is a smaller complex in the electron transport chain.
- Complex II accepts electrons from FADH₂ produced during the citric acid cycle.
- These electrons are transferred to ubiquinone (Q), reducing it to ubiquinol (QH₂).
- Complex II contains: FAD, Iron-sulfur (Fe-S) clusters, Heme b
- Unlike Complex I, Complex II does not pump protons into the intermembrane space.
- This means that electrons entering the ETC via Complex II contribute less to the proton gradient and result in fewer ATP molecules (~1.5 ATP per FADH₂).
- It forms a direct link between the citric acid cycle and the electron transport chain.
Complexes can exist individually, but how else can complexes also exist?
as super-complexes called respirasomes
Describe respiratory super-complexes
- Adapter proteins are needed
- Advantage more efficient transfer
- But too effective might result in reactive oxygen species
- We don’t know much about how this is regulated
What did Peter Mitchell propose in 1961?
That the primary energy-conserving event induced by e- transport is the generation of a proton-motive force across the inner mitochondrial membrane. Basically, that the ETC builds a proton gradient, which indirectly drives ATP synthesis through a proton motive force (PMF).
Why were Pere’s ideas intially met with skepticism?
because researchers at the time expected a chemical intermediate (similar to glycolysis) to directly link the ETC to ATP production.
When did Peter Mitchell receive a nobel prize?
in the late 1970s.
Describe the mechanism of chemeosmosis
- The ETC pumps protons from the matrix into the intermembrane space, resulting in:
Low Proton Concentration: In the matrix (higher pH, more negative charge).
High Proton Concentration: In the intermembrane space (lower pH, more positive charge).
-
Which factors contribute to the proton-motive force
- A concentration gradient : ΔpH ~ -1.4
- A transmembrane potential: Em ~ 0.14 V
How many hydrogen ions are needed for one ATP?
One
What are the 2 parts of ATP synthase?
- F0(membrane part) and F1
- Without F1, F0 pumps protons but does not make ATP
- Isolated F1 hydrolyses ATP (reverse reaction)
- Thus, ATP synthesis requires F0 (proton pumping) and F1 (ATPase) to be coupled
- ATP is formed in the catalytic site of F1 but it is not released unless H+ flow through F0
Describe ATP synthase
protons flow back into the matrix via the F₀ subunit, causing the shaft to rotate.
The rotational energy drives conformational changes in the F₁ subunit, leading to ATP synthesis from ADP and Pi.
Is it true that the ‘Rotation of 𝛾 causes changes in the conformation of the 𝛽 catalytic sites
‘?
Yes
F₀ Unit:
Embedded in the mitochondrial membrane; allows proton flow.
F₁ Unit
Faces the matrix; contains catalytic sites for ATP synthesis.
The γ (gamma) subunit
The γ (gamma) subunit is a central shaft connecting the F₀ and F₁ units.
Rotation of 𝛾
Protons flow down their gradient from the intermembrane space into the matrix through the F₀ unit.
This flow provides the energy needed to rotate the γ shaft.
As the γ shaft rotates, it interacts with the β subunits of the F₁ unit.
This rotation induces conformational changes in the β subunits, which are essential for ATP synthesis.
The β subunits cycle through three states:
O (Open): Allows ADP and Pi to bind or ATP to be released.
L (Loose): ADP and Pi are held loosely, preventing them from escaping. T (Tight): ADP and Pi are forced together to form ATP. ATP is held tightly in this state.
The rotation of the γ shaft changes which β subunit is in each state, allowing continuous synthesis and release of ATP.
The rotation of the γ shaft changes which β subunit is in each state, allowing continuous synthesis and release of ATP.
What controls oxidative phosphorylation?
The need for ATP. Electrons do not flow from NADH to O2 unless ATP is being synthesised .
What determines the rate of respiration?
the level of ADP determines the rate
Uncoupling of the electron transport chain and ATP synthesis, resulting in no ATP synthesis, has been a pharmacological target for decades to combat obesity, but isn’t currently used because……
Temperature of the individual can increase dangerously
What can natural uncoupling generate?
Heat
Describe what thermogenin, the uncoupling protein in animals, does?
Found in mitochondria of brown fat cells
natural uncoupler
maintains body temperature e.g., in babies and during wake up from hibernation
Describe what Alternative oxidase , the uncoupling protein in plants, does?
Oxidises QH2 and generates heat
used by some species to increase temperature of specific organs i.e., flowers or to germinate early
In oxidative phosphorylation, how many ATP are made for each NADH?
2.5 ATP made for each NADH
In oxidative phosphorylation, how many ATP are made for each FADH2?
1.5 ATP made for each FADH2
In respiration, how many ATP are generated per glucose molecule in oxidative conditions?
30
What is the efficiency of respiration?
52%
What goes into the electron transport chain in the mitochondria?
Reduced co enzymes NADH and FADH₂
How many complexes are there?
4
How many proton pumps are there?
3
