Citric acid cycle Flashcards
(30 cards)
what are the other two names for the citric acid cycle?
Krebs or tricarboxylic acid cycle.
what is the citric acid cycle?
involves eight reactions in the mitochondria, therefore, it is anaerobic process meaning it requires oxygen.
what are the three main functions of the citric acid cycle?
- to be an oxidation pathway for CHO, LIP and PRO.
- to generate energy or intermediates (NADH) to be used in the electron transport chain for energy.
- to provide several precursor molecules for other metabolic pathways.
what does the citric acid cycle start with and where does it get this?
acetyl coenzyme A, from macronutrients.
what is the first reaction of the citric acid cycle known as?
link reaction.
what is the first reaction of the citric acid cycle?
the pyruvate formed int he final step of glycolysis is converted to acetyl-coenzyme A via the enzyme pyruvate dehydrogenase complex (PDH) in an irreversible reaction.
this reaction generates 1 NADH.
what type of reaction is the first reaction of the TCA cycle, why?
an oxidation reaction. a carbon is cleaved off of the pyruvate.
what is PDH important for?
both CHO and lipid metabolism during exercise.
is PDH active or inactive?
- PDH exists in an active and inactive form
- active form = non-phosphorylated
- inactive = Phosphorylated
what is PDH inactivated by, how?
PDH kinase, it is up regulates when energy in the cells is plentiful or in low demand.
what is PDH activated by, how?
PDH phosphatase, it is unregulated when energy int he cell is low.
what does phosphorylation allow for?
coupling and addition of a phosphorylation group, not activates or deactivates an enzyme.
how does exercise affect PDH regulation?
exercise activates PDH and increases pyruvate and ADP via glycolysis. muscle contraction during exercise also increases MG+ and Ca^2+ which re both allosteric regulators of PDH.
how does PDH activation relate to the TCA cycle?
PDH activation activates the TCA cycle.
how does NAD+ become NADH?
NAD+ is reduced to NADH by the addition of a hydrogen, where it takes an electron from meaning that it loses the + as it has taken a negatively charged electron and now has a neutral charge.
how does the TCA cycle start?
when oxaloacetate and acetyl-coenzyme A react together.
what is the first step of the TCA cycle?
acetyl-coenzyme A is converted to citrate, via the enzyme citrate synthase.
what is the second step of the TCA cycle?
citrate is converts to iso-citrate, via the enzyme aconitase.
what is the third step of the TCA cycle?
iso-citrate is converted to alpha-ketorgulate, via the enzyme isocitrate dehydrogenase. this generates the first of 3 NADH’s through the oxidation of NAD+.
what is the fourth step of the TCA cycle?
alpha-ketoglutarate is converted to succinyal-coenzyme A, via the enzyme alpha ketoglutarate. this generates another NADH.
what is the fifth step of the TCA cycle?
succinyl coenzyme A is converted to succinate via the enzyme succinyl coenzyme A synthatate. generating the sole ATP from the TCA cycle.
what is the sixth step of the TCA cycle?
succinate is converted to fumoerase via the enzyme succinate dehydrogenase. generates an FADH from an FAD.
what is the seventh step of the TCA cycle?
fumerate is converted to malate via the enzyme fumerate.
what is the eighth step of the TCA cycle?
malate is converted to oxaloacetate via the enzyme malate dehydrogenase. this produces the final NADH.
