Citric acid cycle Flashcards
The citric acid cycle oxidizes —– units, producing two molecules of —– one molecule of ATP, and high-transfer-potential electrons.
- two-carbon
- CO2
Glycolysis takes place in the cytoplasm of the cell, but the citric acid cycle takes place in …….
mitochondria
Pyruvate must therefore be transported into mitochondria to be aerobically metabolized. In the mitochondrial matrix, pyruvate is ………:
oxidatively decarboxylated by the pyruvate dehydrogenase complex to form acetyl CoA
This —— of pyruvate into acetyl CoA is the link between glycolysis and the citric acid cycle
irreversible conversion
Pyruvate dehydrogenasepart of complex+ complex
what it produces
- produces CO2 and captures hightransfer-potential electrons in the form of NADH, thus foreshadowing the key features of the reactions of the citric acid cycle.
- ## a large, highly integrated complex of three distinct enzymes each with its own active site
The mechanism of the pyruvate dehydrogenase reaction is wonderfully complex, more so than is suggested by its simple stoichiometry. The reaction requires the participation of …….
- three enzymes of the pyruvate dehydrogenase complex— pyruvate dehydrogenase, dihydrolipoyl transacetylase, and dihydrolipoyl dehydrogenase—as well as five coenzymes.
Catalytic Coenzyme
small molecule bound to the enzyme that is required for enzyme activity but not permanently altered by the reaction
The conversion of pyruvate into acetyl CoA consists of three steps:
These steps must be —— to preserve the free energy derived from the —– step to drive the formation of NADH and acetyl CoA
- decarboxylation, oxidation, and the transfer of the resultant acetyl group to CoA.
- coupled
- decarboxylation
Decarboxylation of pyruvate (4)
what happens/yields+this reaction is known as+enzyme+ what is it part of
- Pyruvate combines with the ionized (carbanion) form of TPP and is then decarboxylated to yield hydroxyethyl-TPP.
- This reaction, the rate-limiting step in the synthesis of acetyl CoA, is catalyzed by the pyruvate dehydrogenase component (E1) of the multienzyme complex.
- TPP is the coenzyme of the pyruvate dehydrogenase component.
Oxidation step of Pyruvate (3)
What happens+ catalyzed by + yields
- The hydroxyethyl group attached to TPP is oxidized to form an acetyl group while being simultaneously transferred to lipoamide
- The reaction, also catalyzed by the pyruvate dehydrogenase component E1 yields acetyl–lipoamide
Formation of acetyl CoA of Pyruvate (2)
What heppens+ who catalyzes?
- The acetyl group is transferred from acetyl–lipoamide to CoA to form acetyl CoA.
- Dihydrolipoyl transacetylase E2 catalyzes this reaction.
The pyruvate dehydrogenase complex cannot complete another catalytic cycle until ……. This is done by …..
- the dihydrolipoamide is oxidized to lipoamide.
- the oxidized form of lipoamide is regenerated by dihydrolipoyl dehydrogenase E3
Dihydrolipoamide (—– form) must be —— back to lipoamide (—— form). FADH2 (reduced form) must be —–back to FAD (oxidized form). Ultimately, —–
is produced
- reduced
- re- oxidized
- oxidized
- re- oxidized
- NADH
Acetyl-CoA can either (2):
- Oxidation through TCA cycle (to generate ATP)
- Incorporation into fatty acids
High concentrations of reaction products inhibit the reaction:ex: (2)
High concentrations of reaction products inhibit the reaction: acetyl CoA inhibits the transacetylase component E2 by directly binding to it, whereas NADH inhibits the dihydrolipoyl dehydrogenase E3
Phosphorylation of the pyruvate dehydrogenase component :
+when
- E1 by pyruvate dehydrogenase kinase switches off the activity of the complex. Deactivation is reversed by the action of pyruvate dehydrogenase phosphatase.
- At rest, the muscle will not have significant energy demands. Consequently, the NADH/NAD+, acetyl CoA/CoA, and ATP/ADP ratios will be high. These high ratios stimulate pyruvate dehydrogenase kinase, promoting phosphorylation and, hence, deactivation of the pyruvate dehydrogenase complex.
Tricarboxylic Acid (TCA) Cycle or Citric Acid Cycle (CAC)
what happens (final prod)+what is produced+e-
Step 1 of CAC (4):
What happens/forms+ how its done+ net+enzyme
i- Acetyl-CoA (2C) and oxaloacetate (4C) joins together to form citrate (6C) (intermediate)
- Hydrolysis removes CoA
NET:
-H2O
+CoA
- catalyzed by citrate synthase
Step 2 of CAC:
What happes+ what the steps do?+ enzyme
- Citrate turns into cis-aconitate through dehydration reaction
- cis-aconitate turns into iso-citrate through hydration reaction
- These two steps switches the OH group from C3 to C2
- enzyme is aconitate
Step 3 of CAC (4)
enzyme+the 2 rxns+net
- carried by enzyme isocitrate dehydrogenase
- First reaction includes taking a pair of electron to form oxalosuccinate (make NADH)
- Decarboxylation reaction with oxalosuccinate and H+ ion to form a-ketoglutarate
- NET:
+CO2
+NADH
Step 4 of CAC (2):
what happens+ enzyme
- conversion of a-ketoglutarate into succinyl coenzyme A via oxidative decarboxylation
- enzyme: α- Ketoglutarate Dehydrog ena s e Complex (structurally similar to pyruvate dehydrogenase, use the same coenzymes and catalyze decarboxylation and linkage to CoA)
Step 5 of CAC: (3)
What happens+ enzyme+net
- succinyl coenzyme A has it’s energetic thioester bond cleaved off to drive ATP production
- Enzyme is Succinyl - CoA Synthetase
- NET:
-Pi
+CoA
+ATP
Step 6 of CAC (3):
What happens+ enzyme+ Net
- O-R reaction that oxidizes succinate into fumarate while taking out 2H+ ions and a pair of electrons to form FADH2
- enzyme: Succinate Dehydrog ena s e
- NET:
+FADH2
Step 7 of CAC (3):
Enzyme+what happens+net
- Enzyme: Fumarase
- Fumarase catalyzes the hydration of fumarate into malate
- Net: -H2O
Step 8 of CAC (3):
What happens+enzyme+net
- Malate Dehydrogenase oxidizes malate into oxaloacetate and transfer electrons onto NADH (Oxaloacetate is regenerated, and TCA may continue)
- NET:
+NADH
