2.6 Cell Integrity Flashcards
Generation of ATP and ATP equivalents through the use of kinases is known as what?
Substrate level phorphorlyation
What is it called when the electron transport chain reduces oxygen to water, coupling proton pumping to ATP production via ATP synthase?
Oxidative phosphorylation
Where do the reactions of oxidative phosphorylation occur?
In the inner membrane which folds and creates inward projections called cristae
What is the ΔG of the reoxidation of NADH?
-223 kJ/mol
What is the ΔG for the reoxdidation of FADH2?
-170 kJ/mol
What is the ΔG for ATP hydrolysis?
-31kJ/mol
In terms of energy, how does the oxidation of NADH and FADH2 lead to several ATP being produced?
The energy released from the re-oxidation of NADH and FADH2 (-223 and -170 kJ/mol) is enough to generate several phosphoanhydride bonds
As ATP hydrolysis releases -31 kJ/mol
What is the name of complex I membrane protein?
NADH dehydrogenase
What is the name of complex II membrane protein?
Succinate dehydrogenase
What is the name of membrane protein complex III?
Q-cytochrome C oxidoreductase
What is the name of Membrane protein complex IV?
Cytochrome c oxidase
What are the names of the two mobile carriers in the inner membrane of the mitochondria?
Co-enzyme Q (ubiquinone) and Cytochrome C
Which static membrane proteins can pump hydrogen ions into the inter-membrane space?
Complex 1, 3 and 4
Which complex does NADH pass its electron to?
Complex I NADH dehydrogenase
Which complex does FADH pass its electrons to?
Complex II succinate dehydrogenase
What happens when the membrane proteins accept electrons?
They can pump protons from the matrix into the intermmebrane space
Why does the deoxidation of FADH produce less ATP than NADH?
FADH passes its electrons directly to complex 2 (complex 1 is bypassed), meaning less H+ ions are pumped across
Since it is the flow of H+ ions which generates ATP, less H+ means less ATP
What are redox reactions?
Electron transfer reactions involving a reduced substrate (which donates electrons and therefore becomes oxidised) and an oxidised substrate (or oxidant) which accepts electrons and becomes reduced in the process
What is the redox potential?
The ability of a redox couple to accept or donate electrons
What does a negative redox potential indicate?
A high reducing power - this means the redox couple has a tendency to donate electrons to be gained by other substances, therefore reducing them
What does a positive redox potential indicate?
The redox couple has higher oxidising power than hydrogen, and therefore has a tendency to accept electrons, as it makes other things become oxidised (as they lose electrons
What happens as electrons as passed from one complex to another down the chain?
The electrons lose energy - meaning this transfer is energetically favourable
What happens to coenzyme Q when electrons are passed from FADH2 to it?
Q becomes reduced to QH2
What is ATP synthase?
A multimeric enzyme which consist of a membrane bound part F0 and an F1 part which projects into the matrix space
What does the direction of protein flow in ATP synthase dictate?
Whether it is ATP synthesis or hydrolysis
What happens to the energy which is stored in the electrochemical gradient of protons?
It is converted into mechanical rotational energy to drive the ATP synthase molecule around
What happens as ATP synthase rotates?
The affinities for ATP and ADP change
Conformational energy flows from the catalytic subunit into bound ADP and Pi to convert it into ATP
What happens when the concentration of H+ ions is higher in the matrix than in the intermembrane space?
ATP synthase will work in the other direction
ATP is hydrolysed to ADP and Pi
What is the function of the F0 unit in ATPsynthase?
Rotates, coverting mechanical energy into kinetic energy
What is the function of the F1 subunit of ATP synthase?
Synthesises ATP from ADP and Pi
What is the current across the oxygen electrode proportional to?
The oxygen concentration in the sample chamber
What happens when ADP is added to the sample of prepared mitochondria?
There is a rapid consumption of oxygen as the ADP is used up for oxidative phosphorylation
Why is the current that arises from the oxygen electrode proportional to the oxygen concentration in the sample chamber?
The oxygen diffuses through the teflon membrane and is reduced to water at the platinum cathode
Therefore the more that is reduced, the greater the current
What is uptake of O2 controlled by in the mitochondria?
Inorganic phosphate and ADP
What is respiratory control?
Uptake of oxygen by mitochondria is controlled by the components of ATP production: Inorganic phosphate (Pi), and ADP.
What is meant by a metabolic poison?
A molecule which interferes with the flow of electrons along the ETC or the flow of protons through ATP synthase
How does Cyanide (CN-) and Azide work as a metabolic poison?
Bind with high affinity to the ferric (Fe3+) form of the haem group in the cytochrome oxidase complex blocking the final step of the ETC
What step of the electron transport chain does Cyanide and Azide interfere with?
The final step as the electrons cannot be passed onto the cytochrome oxidase complex
How does malonate work as a metabolic poison?
Closely resembles succinate and acts as a competitive inhibitor of succinate dehydrogenase - slows down the flow of electrons from succinate dehydrogenase to ubiquinone
How does rotenone work as a metabolic poison?
It inhibits the transfer of electrons from complex I to ubiquinone
How does oligomycin work as a metabolic poison?
Inhibits oxidative phosphorylation by binding to the ‘stalk’ of ATP synthase and blocking the flow of protons through the enzyme
How does dinitrophenol work as a metabolic poison?
It can shuttle protons across the inner mitochondrial membrane, bypassing ATP synthase and uncoupling oxphos from ATP production
This increases metabolic rate and body temperature
Why does the respiratory rate and body temperature increase when DNP causes bypass of ATP synthase?
The energy to pump H+ is dissipated as heat instead of forming ATP
Which metabolic poison effects Complex I?
Rotenone
Which metabolic poison works on Complex 4?
CN- and Azide ions
Which metabolic poison works on ATP synthase?
Oligomycin
How can DNP induce weight loss?
Transporting H+ ions across the membrane
Uncoupling oxidative phosphorylation from ATP production and therefore increasing metabolic rate
The body uses more fuel to pump H+ ions to restore the electrochemical gradient, leading to weight loss
Why are fewer ATP molecules produced when FADH2 is reoxidised by the electron transport chain compared with NADH?
Complex I is bypassed and fewer protons are pumped to the intermembrane space
The metabolic poison rotenone inhibits the oxygen consumption of mitochondrial suspensions metabolising citrate. However, it has little effect upon the oxygen consumption of a suspension of mitochondria metabolising succinate - why?
Rotonone does not inhibit complex II of the electron transport chain
Why does glucose have no effect on the Oxygen concentration in the oxygen electrode experiment?
Metabolism of glucose occurs in the cytoplasm - this means the enzymes needed to break it down are in the cytoplasm not the matrix
What affect does adding citrate have on the Oxygen Consumption during the oxygen electrode experiment?
Citrate is part of the TCA cycle - this means NADH and FADH can be produced
This coupled with proton pumping makes ATP so oxygen is CONSUMED
What happens when DNP is added to the sample in the oxygen electrode?
Separates electron transport chain from oxidative phosphorylation
H+ ions can still flow and combine with oxygen to make water, so CONSUMPTION INCREASES
Why does adding rotenone slow but not halt oxygen consumption?
When you still have succinate which donates to Complex II, so some oxygen is still consumed as rotenone only blocks complex I
Why does the addition of cyanide to the oxygen electrode cease the electron chain?
It blocks the flow of H+ ions through ATP synthase, meaning the entirety of the electron transport chain is backed up
What is the half equation representing the production of oxygen from hydrogen and oxygen?
2H+ + 1/2 O2 —-> H2O
What is oxygen considered in the electron transport chain?
The final electron acceptor
How can we use the Oxygen Electrode to measure changes in ETC?
By placing suspension of mitochondria into chamber, we can see effects of various substrates and inhibitors on ETC through changes in [O2]
Why did people taking DNP die?
The margin between a helpful and fatal dose was very small
How does substrate level phosphorylation differ from oxidative phosphorylation?
Oxidative phosphorylation utilises the electron transport chain
How does NADH and FADH2 get into the mitochondrial matrix?
They use the malate and aspartate shuttle, as well as the glycerol phosphate shuttle
What is the order of how the electrons are passed on in the electron transport chain?
Complex 1: NADH Dehydrogenase and Complex 2: Succinate dehydrogenase
Both pass to Q - Ubiquinone
Complex 3: Q-Cytochrome c oxidoreductase
Cytochrome c
Complex 4: Cytochrome oxidase
Describe how malonate works as it has a similar chemical structure to succinate?
- It has a similar chemical structure to succinate
- This means it binds to succinate dehydrogenase instead of succinate
- Therefore, succinate deydrogenase cannot convert succinate into fumerate and hence less FADH2 is produced
- Hence the flow of electrons from FADH2 to Q is slowed
Explain uncoupling in non-shivering thermogenesis?
UCP-1 a.k.a. thermogenin, is activated in response to a drop in core body temperature.
Like DNP it allows protons to bypass ATP synthase thereby releasing heat from the dissipation of the proton gradient.
