Citric acid Cycle - RM Flashcards
Where does over 90% of ATP production in aerobic conditions occur? What two processes contribute to it?
mitochondria, CAC and oxidative phosphorylation
What cells have the most mitochondria? Why?
cells with high energy needs
heart for contraction
kidney for transport
liver for biosynthesis
Why are mitochondria located near structures requiring ATP?
decreases the diffusion path from where ATP is made to where it’s needed, speeds process
Which mitochondrial membrane is the permeability barrier?
inner mitochondrial membrane
What enzymes are embedded in the inner mitochondrial membrane? Which way do they face?
oxidative phosphorylation enzymes, facing matrix
What occurs in the matrix of the mitochondria?
citric acid cycle, oxidative phosphorylation
What two molecules can diffuse freely without a transport system between the matrix of the mitochondria and the cytoplasm?
oxygen and carbon dioxide
What is there no transport system for across the mitochondrial matrix? What is the result of this?
NADH, it is compartmentalized into matrix NADH and cystolic NADH–reducing equvialents are shuttled between the two to reduce matrix NADH as fuel for oxidative phosphorylation
What are the three functions of the citric acid cycle?
converts many fuels into common mobile fuel (NADH)
serves as final meeting place of all oxidizable substrates
provides intermediates for biosynthesis
What enzyme oxidizes pyruvate? What does it form? Where does the reaction occur?
pyruvate dehydrogenase complex, acetyl coA, mitochondrial matrix
What is referred to as the link between glycolysis and citric acid cycle?
pyruvate dehydrogenase complex (converts end product of glycolysis pyruvate into starting substrate of CAC acetyl coA)
What is E1 of the pyruvate dehydrogenase complex? What type of reaction does it catalyze? What is its prosthetic group?
pyruvate dehydrogenase, condensation/decarboxylation, TPP
What is E2 of the pyruvate dehydrogenase complex? What type of reaction does it catalyze? What is its prosthetic group?
dihydrolipoyl transacetylase, 2 reactions: oxidative transfer, transacetylation, lipoamide
What is E3 of the pyruvate dehydrogenase complex? What type of reaction does it catalyze? What is its prosthetic group?
dihydrolipoyl dehydrogenase, dehydrogenation, FAD
What is TPP? Can we make this?
thiamine pyrophosphate, no- must obtain thiamine from diet
What molecule would accumulate in your blood if you have beriberi?
pyruvate (can’t metabolize it without TPP)
Why does lipoamide have a reactive disulfide bond?
the 5 membered ring puts strain on S-S
What does dihydrolipoyl dehydrogenase do in the reaction if acetyl coA has already been formed?
reoxidizes dihydrolipoamide to lipoamide using FAD so the reaction can proceed again
Why does the swinging arm model for the pyruvate dehydrogenase complex confer an advantage?
makes it kinetically efficient since the substrates and enzymes don’t have to float around till they find each other (multiple lipoamides are used per E2 to make spacing work), not limited by diffusion
How does arsenite kill?
forms chelation complex with reduced lipoamide (dihydrolipoamide) to poison the cofactor–won’t be able to survive since you can’t do oxidative phosphorylation without the citric acid cycle
What does citrate synthetase do?
condenses acetyl coA and OAA and cleaves a thioester bond to form citrate and coA
Is the hydrolysis of the thioester by citrate synthetase wasteful since it releases -7.5 kcal/mol?
no, it is used later to pull along malate dehydrogenase reactions
What does aconitase do? Why?
dehydrates citrate and rehydrates it to isocitrate, moves hydroxyl to a secondary carbon from a tertiary one so it can be oxidized in the next step
Why does the aconitase reaction produce isocitrate if it favors citrate 10:1?
isocitrate is removed in the next step (lechatliers principle)
What kind of center does aconitase have?
iron-sulfur center
What does isocitrate dehydrogenase do? What are the products?
oxidative decarboxylation of isocitrate, produces alpha-ketoglutarate (with OAA intermediate) and NADH
Why does alpha-ketoglutarate undergo the same 4 step reactions as pyruvate via the alpha-ketoglutarate complex?
it has the same structure, just with an added CH2-COOH
What does alpha-ketoglutarate get converted to by the alpha-ketoglutarate dehydrogenase complex?
succinyl coA, NADH, CO2
What does succinyl coA synthetase do? What cofactor does it use?
cleaves the thioester bond of succinyl coA to produce GTP, uses coA cofactor
-substrate level phosphorylation
Which reaction in the citric acid cycle demonstrates the common intermediate principle? How?
succinyl coA synthetase, it displaces coA to bind succinyl-phosphate (E-succinyl phosphate), transfer phosphate to histidyl residue on E and release succinate (E-P), to regenerate enzyme transfers P to GDP to form GTP and E
What does succinate dehydrogenase do? What is unique about this reaction?
oxidizes succinate to fumarate, complex is bound to IMM and transfers electrons to FAD (directly into electron transport chain) rather than NADH (mobile electron carrier)
What does fumarase do?
hydrates fumarate to form malate
What does malate dehydrogenase do? Is this reaction favorable? How does it occur?
oxidizes malate to oxaloacetate (OAA), not favorable (+7.1 kcal/mol), gets pulled along by citrate synthetase reaction releasing energy it can use
Why is it favorable to have a large malate pool and a small OAA pool in resting state?
malate can exit to the cytoplasm and serve as a substrate for gluconeogenesis while OAA cannot
