6. Energy Production - Carbohydrates (c) Flashcards
What makes a step a key regulatory one?
If it’s irreversible.
What activates pyruvate dehydrogenase?
Pyruvate, CoASH, NAD+, ADP, insulin, dephosphorylation.
What inhibits pyruvate dehydrogenase?
Acetyl-CoA, NADH, ATP, citrate, phosphorylation.
What can a deficiency of pyruvate dehydrogenase lead to?
Lactic acidosis.
Where does the Kreb’s cycle take place?
In the mitochondria.
Is the TCA cycle oxidative or reductive?
Oxidative, it requires NAD+ and FAD.
What three key things come from the TCA cycle?
CO2 (from acetyl CoA), energy (in form of ATP and GTP) and precursors for biosynthesis.
How many cycles of the TCA cycle happen per glucose molecule?
2.
What is the overall equation for one turn of the Kreb’s cycle?
CH3CO~CoA + 3NAD+ + FAD + GDP + Pi + 2H2O –> 2CO2 + CoA + 3NADH + 3H+ + FADH2 + GTP
What regulates the TCA cycle?
Energy availability, the ATP/ADP ratio and NADH/NAD+ ratio.
What biosynthetic processes does the TCA cycle provide precursors for?
Amino acid, fatty acid and haemoglobin synthesis.
What is driven when NADH and FADH2 are oxidised?
Synthesis of ATP.
What two methods use the reducing power to produce ATP?
Electron transport (energy released in steps) and oxidative phosphorylation (free energy drives ATP synthesis).
Talk through the key steps in mitochondrial electron transport.
There are three proton trans locating complexes.
PTC1: NADH + H+ (2H+ + 2e-) –> NAD+ + 2e- + 2H+
PTC2: FADH2 (2H+ + 2e-) –> FAD + 2e- + 2H+
PTC3: 2H+ + O + 2e- –> H2O.
In every case, the two electrons produced go to the inner mitochondrial membrane and the two hydrogen ion go to the inter membrane space.
What is 30% of the energy released from the electron transport through carrier molecules used for?
To move H+ across the membrane.
What is the proton motive force?
The [H+] gradient across the inner mitochondrial membrane.
What do the H+ travel through when moving down their electrochemical gradient across the membrane?
ATP synthase.
How is the proton motive force generated for oxidative phosphorylation?
When electrons are transferred from NADH and FAD2H to oxygen (the final electron carrier) energy is released. This is used to move hydrogen ions and create the pmf.
How many proton translocation complexes do NADH and FADH2 use respectively? Why do they use different numbers?
NADH uses 3 but FADH2 only uses 2 because NADH electrons have more energy than FADH2.
How is oxidative phosphorylation regulated?
If ATP is high, then ADP must be low so there is no substrate for ATP synthase. This means the inward flow of H+ stops and the concentration of H+ in the intermitochondrial space increases. Further H+ pumping is prevented and electron transport stops.
How is oxidative phosphorylation inhibited?
By inhibitors blocking electron transport so acceptance of electrons by O2 is prevented.
What is the effect of uncouplers on oxidative phosphorylation?
Uncouplers increase the permeability of the mitochondrial inner membrane to protons. This dissipates the proton gradient so the pmf is reduced and there is no drive for ATP synthesis.
What are the three ways of inhibition oxidative phosphorylation?
Inhibiting electron transport so there is no pmf and no oxidative phosphorylation. Uncouplers that increase permeability of membrane to H+ so there is no pmf or drive to synthesise ATP and no oxidative phosphorylation. Ox/phos disease caused by genetic defects leading to decrease electron transport and ATP synthesis.
How does the efficiency of coupling of oxidative phosphorylation vary?
Some of the energy is lost by heat. In brown adipose tissue uncouplers allow for extra heat generation.
How do brown adipose tissue release more heat energy?
They have naturally occurring uncoupling proteins, thermogenin. In the cold, noradrenaline activates lipase which releases fatty acids form TAGs. There is fatty acid oxidation, forming NADH and FADH2 and causing electron transport. UCP1 is activated so H+ is transported back into the mitochondria. Extra energy from uncoupled electron transport ATP synthesis is released as extra heat.
What two organisms are high brown adipose tissue levels found in?
In newborn infants and hibernating animals.
What are four key difference between oxidative phosphorylation and substrate level phosphorylation.
1) OP requires membrane associated complexes but SLP requires soluble enzymes.
2) Energy coupling happens indirectly through generation and utilisation of the pmf in OP but happens directly from formation of high energy hydrolysis bonds in SLP.
3) OP must happen aerobically whereas SLP can happen to a limited extent in anaerobic conditions.
4) OP is a major process of ATP synthesis in cells that require lots of energy, but SLP is only used when OP is unavailable for that cell so doesn’t happen in cells requiring lots of energy.
What enzyme catalysed the conversion of pyruvate to acetyl CoA?
Pyruvate dehydrogenase.
