Sesh 2- TCA cycle and oxidative phosphorylation Flashcards
(22 cards)
Where does the TCA cycle occur?
Mitochondrial matrix
Why are there no known genetic defects in the TCA cycle?
They would be lethal, as it is a central pathway of catabolism.
Apart from its role in the TCA cycle, what else can citrate be used for?
Fatty acid synthesis
What is the role of pyruvate carboxylase?
Converts pyruvate to oxaloacetate
Which 2 ratios are used to control the TCA cycle?
- ATP:ADP
- NADH: NAD+
What reaction does isocitrate dehydrogenase catalyse?
The irreversible conversion of isocitrate to alpha-ketoglutarate
What are the 2 major functions of the TCA cycle?
- Break all C-C bonds in acetyl CoA
- Oxidise C atoms to CO2
Which carrier molecule contains the highest energy electrons?
NADH
What is the net yield of ATP from one mole of glucose?
32 ATP
Where does oxidative phosphorylation occur?
Inner mitochondrial membrane
Why can the electron transport chain only occur in the presence of oxygen?
Oxygen is the terminal acceptor of electrons.
What is normally the only way that protons can re-enter the mitochondrial matrix?
Via the ATP synthase complex.
How is the proton motive force generated?
Electrons are transferred from NADH/FADH2 sequentially to proton translocating complexes, which use this free energy to drive H+ into the intermembrane space.
Why does FADH2 yield less ATP compared to NADH?
The electrons in FADH2 contain less energy, so it feeds in to the electron transport chain at proton translocating complex 2 rather than 1.
What does the efficiency of ATP synthesis in oxidative phosphorylation depend on?
How impermeable the inner mitochondrial membrane is to H+, as this affects generation of the proton motive force.
How does the proton motive force affect the relative production of ATP?
Greater the proton motive force, more ATP produced.
What happens to oxidative phosphorylation, and therefore the rest of glucose metabolism when [ATP] is high?
- Means [ADP] is low, so ATP synthase stops working
- Leads to buildup of H+ in inter membrane space, so proton translocating complexes stop
- This prevents re-oxidation of carriers, so negative feedback on prior pathways
How does dinitrophenol lower ATP production?
Uncouples electron transport chain from ATP synthesis by increasing inner mitochondrial membrane permeability to H+. Less of a proton motive force is set up and more energy is lost as heat.
What is the role of Uncoupling Protein 1 (UCP1)?
Expressed in brown adipose tissue, to uncouple electron transport from ATP synthesis by increasing inner mitochondrial membrane permeability to H+.
More energy lost as heat for non-shivering thermogenesis.
How does cyanide inhibits the electron transport chain?
Binds the haem group of the terminal proton translocating complex (cytochrome C oxidase), meaning O2 cannot bind and act as the terminal electron acceptor.
Which molecule combines with acetyl CoA to form citrate in the first step of the TCA cycle?
Oxaloacetate
Which stage in the metabolism of glucose produces the most ATP?
Electron transport chain
