week 3 citric acid cycle & terminal respiration (revised) Flashcards
where does the citric acid cycle occur
- mitochondrial matrix
what is the point in the citric acid cycle
- removes electron and passes them on to form NADH and FADH2
- these then pass electrons onto the electron transport chain which creatives a force which drives ATP synthase
how is acetyl coA formed
- pyruvate > acetyl coA , via pyruvate dehydrogenase
- series of reactions involving decarboxylation of pyruvate, then oxidation, followed by transfer of coA complex
- decarboxylation step releases two electrons which can pass to oxygen to form ATP through NADH intermediates
what does acetyl coA do
allows different intermediates into the citric acid cycle
what is the stucture of pyruvate dehydrogenase
- made up of three subunits called E1, E2 E3
- each subunit catalyses a different part of the reaction to convert pyruvate to acetyl coA
what does subunit E1 of pyruvate dehydrogenase do
- catalyses the first decarboxylation of pyruvate
what does subunit E2 of pyruvate dehydrogenase do
- transfers the acetyl group to coA
what does subunit E3 of pyruvate dehydrogenase do
- recycles the lipoyllysine through the reduction of FAD, which is recycled by passing electrons to NAD
what happens at each turn of the citric acid cycle
- at each turn 2 carbons (acetyl coA) enter
- 2 different carbons exit the cycle in the form of 2x CO2
- 3 NADH and 1 FADH2 also leave
how is entry into citric acid cycle controlled
pyruvate dehydrogenase is regulated
- inhibited by ATP if the cell has enough energy
- activated by ADP + Pi if the cell needs energy
what are the two points of control in the citric acid cycle
- iso citrate > alpha-ketoglutarate, via isocitrate dehydrogenase
- inhibited by ATP and NADH
- activated by ADP - alpha-ketoglutarate > succinyl coA, via alpha-ketoglutarate dehydrogenase
- inhibited by ATP, NADH and succinyl coA
what does inhibition of isocitrate dehydrogenase in citric acid cycle cause
- citrate build up which shuttles citrate into cytoplasm causing phosphofructokinase to stop glycolysis
what does inhibition of alpha-ketoglutarate dehydrogenase in the citric acid cycle cause
- causes alpha-ketoglutarate build up which switches its use to production of amino acids
what do they mean by saying that the citric acid cycle is amphibolic
- it is anabolic and catabolic
where does terminal respiration (electron transport chain) occur
- on the inner mitochondrial membrane
what electron carrying molecules do you get from glycolysis
- NADH + H+
- ATP
what electron carrying molecules do you get from pyruvate > acetyl coA reaction
- NADH + H+
what electron carrying molecules do you get from each turn of citric acid cycle
- 3 NADH + H+
- 1 FADH2
- 1 GTP
what electron carrying molecules do you get from beta oxidation of fatty acids
- 1 NADH + H+
- 1 FADH2
what is the job of the glycerol phosphate shuffle
- NADH can’t get through outer membrane to electron transport chain so FADH2 passes the electrons on for it, this is the glycerol phosphate shuffle
- majority of NADH and FADH2 is formed in the mitochondrial matrix, it has to be there to be oxidised, but some of NADH is formed in the cytoplasm so FADH2 transports its electrons for it since it can’t cross
what are the steps in the glycerol phosphate shuffle
- NADH + H+ > NAD+ as it loses electrons
- dihydroxy acetone phosphate becomes glycerol 3 phosphate as it holds the electrons from NADH + H+
- glycerol 3 phosphate passes the electrons to FAD which becomes FADH2 at the outer mito. membrane
- FADH2 passes electrons to electrons transport chain on the inner mitochondrial membrane
what is the downside to the glycerol phosphate shuffle
- oxidation of FADH2 in electron transport chain generates, per mol, less ATP than NADH
- this energetic ‘price’ is paid for using cytosolic reduced co-substrates in terminal respiration
what is the order of the complexes in the electron transport chain
complex 1 = NADH-Q oxidoreductase
complex 2 = succinate-Q reductase
- then ubiquinone/Q pool (but this isn’t a complex, becomes ubiquinol once it has electrons passed to it)
complex 3 = Q cytochrome c oxidoreductase
complex 4 = cytochrome c oxidase
what happens at complex 1 (NADH-Q oxidoreductase) of the electron transport chain
- oxidises NADH
- passes the electrons to ubiquinone which becomes ubiquinol (QH2)
- utilises Fe-S centres and FVM
- pumps H+ into intermembrane space
