Lect 6 - Oxidative phosphorylation Flashcards
What are the 2 parts of oxidative phosphorylation?
- Electron transport chain
- Chemiosmosis
What is meant by chemiosmosis?
it is the movement of ions (protons) from an area of higher concentration (intermembrane space) to an area of lower concentration (mitochondria matrix) across a semi-permeable membrane (inner membrane).
Certain compounds have ability to increase permeability of inner mitochondria membrane. What effect does this have on :
1. Electron transport?
2. ATP synthesis?
- No effect on electron transport, can still carry out as per usual
- Inhibits synthesis, as increased permemability of membrane causes the collapse of the proton gradient (by allowing ions to flow through freely and bypassing atp synthase
ATP synthesis is harnessed through an electrochemical gradient. What are the 2 components of an electrochemical gradient and their definitions?
- Electrical potential : difference in charge across inner mitochondria membrane.
- Chemical potential : difference in pH across inner mitochondria membrane.
What is the function of ATP synthase?
It synthesises ATP from ADP and Pi through utilising energy derived from the proton gradient.
ATP synthase is made up of which 2 subunits?
F0 and F1 subunit
What does the F0 subunit of ATP synthase consist of?
F0 subunit is the part embedded in the inner mitochondrial membrane, consisting of :
- C-ring
- “a” subunit
What does the F1 subunit of ATP synthase consist of? [5]
F1 subunit is the portion protruding into the membrane and consist of catalytic sites for ATP synthesis.
1. γ subunit
2. δ subunit
3. ε subunit
4. α subunit
5. β subunit
The γ,δ, ε subunits make up the stalk (which rotates), and the catalytic head is made up of 6 subunits : 3α + 3β subunits.
Describe the process of how ATP synthase synthesises ATP.
- Protons bind to the C-ring, causing rotation of the C-ring. (After rotation, protons are released into mitochondrial matrix)
- This in turn causes the γ-subunit in the F₁ catalytic domain to rotate.
- The rotation of the γ-subunit indues conformational change in the three catalytic β-subunits of ATP synthase, causing ATP to be synthesised from ADP + Pi
How are protons translocated from the inter membrane space into the mitochondrial matrix through the C-ring rotation?
Hint : amino acid residues on “a” subunit and C-ring
- Initially, glutamate residues (-) in the C-ring interact with arginine residues (+) in the “a” subunit.
- As protons flow in from the intermembrane space, H+ binds to glutamate residues in C-ring. Glutamate is no longer negatively charged and repels arginine residues, causing a 360° rotation in the C-ring
- As protons detach from glutamate residues, and glutamate interacts with the arginine residue again
How many ATP molecules are synthesised per rotation of the C-ring?
3
How is oxidative phosphorylation (ATP synthesis) regulated?
Hint : regulated through concentrations of ___ and ___? (ratios)
It is mainly regulated through the energy requirements of the cells.
1. [ATP] / [ADP] ratio : when [ATP] / [ADP] is high, it means that the cell has sufficient energy. Since [ATP] is high, and [ADP], the substrate for ADP synthase is low, ATP generation by ATP synthase slows down
- [NADH]/[NAD+] ratio : when [NADH]/[NAD+] is high, it signifies that ATP production is low. Thus, high ratio activates oxidative phosphrorylation since there are more substrates (NADH) available to be oxidised.
In general, how are ATP levels correlated with NADH levels?
- When there is high ATP levels, there is low NADH. (NADH utilised for ATP synthesis)
- When there is low ATP levels, there is high NADH
What will happen if Rotenone, inhibitor of complex I is added to a mitochondria preparation?
- Since complex I is inhibited, it blocks the transfer of electrons from NADH to uniquinone (Coenzyme Q), which stops the pumping of protons into the intermembrane space by Complex I
- ATP production by oxidative phos is inhibited
- Also causes a buildup of NADH and reduction of available NAD+, which can inhibit other processes that require NAD+
What will happen if antimycin A is added, an inhibitor of complex III?
It blocks transfer of electrons from ubiquinone (Coenzyme Q) to cytochrome c.
- This prevents pumping of protons into intermembrane space by complex III, and
- causes a backup of electrons, leading to production of reactive oxygen species (ROS) which can be harmful to the cell.
What will happen if cyanide is added, an inhibitor of complex IV?
- Cynaide inhibits Complex IV (cytochrome c oxidase) by binding to its heme group, preventing transfer to oxygen, the final electron acceptor
- The ETC is halted and stops production of ATP by oxidative phosphorylation.
