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Flashcards in TCA Deck (70):

What does TCA strip electrons from? What does it produce?

Pyruvate, Carbon dioxide, respectively


How are the electrons in TCA recovered?



How many GTP’s are produced in TCA? ATP?



What key intermediate feeds into the TCA cycle ? (Hint: comes from PDH complex)

Acetyl Coa


Where does TCA take place in the mitochondria?



What enzyme is bound to mitochondrial inner membrane?

Succinate DH


Name the three enzymatic portions of PDH

Pyruvate decarboxylase (E1), dihydrolipoyl transacetylase (E2), dihydrolipolyl dehydrogenase (E3)


What cofactor used in PDH complex catalyzes attack on alpha carbon of pyruvate by delocalizing electrons from a carbanion?

Thiamine pyrophosphate (TPP)


What co factor acts as a long tethering arm to move acetelaldehyde?

Lipoic acid


How does E3 capture high energy electrons?

Takes them off lipoic acid first via FADH2 and then transfers to NADH


What is the starting point for TCA cycle?

Acetyl Coa


What is the first rx. of TCA?

Condensation of OAA with acetyl Coa to form citrate via citrate synthase


What enzyme catalyzes cleavage of citrate in the cytosol to produce acetyl coa for fatty acid synthesis?

Citrate lyase


What are the two different pathways of TCA that are joined together?

1st takes acetyl Coa plus OAA and makes alpha ketoglutarate, second takes OAA and makes succinyl coa for heme synthesis, when alpha ketoglutarate DH evolved it made this a cycle


What enzyme is alpha ketoglutarate very structurally similar to?

Pyruvate dehydrogenase complex


What enzyme shifts the hydroxyl on citrate



Does aconitase have an iron sulfur cluster?



Name the steps in TCA that produce reducing equivalents

Isocitrate DH, alphaketoglutarate DH, succinate DH (FADH), malate DH


What step produces GTP?

Succinyl coa synthetase


Can TCA get started without any intermediates?

No, has to have a few catalytic precursors


For each turn of TCA how many carbons enter and leave?

2 carbons enter via acetyl coa, 2 carbons leave via carbon dioxide


What is the only 5 carbon compound in TCA?

Alpha ketoglutarate


Does FA synthesis put a drain on TCA?

Yes, it pulls citrate out for precursors


What is the alpha keto acid of pyruvate?



IF pyruvate were to be used for biosynthesis what would it be converted to? If it was going to be used for energy production what would it be converted to?

OAA, acetyl coa, respectively


What inhibits PDH?

Acetyl Coa, NADH, ATP


What are the three regulated steps in TCA besides PDH?

Isocitrate dh, alphaketogluatate DH, citrate synthase


What is the glyoxylate cycle?

Allows for carbohydrate synthesis via 2 carbon intermediates of TCA, forms acetyl coa and malate which can be used in gluconeogenesis


What unique enzymes does the gloxylate cycle have?

Isocitrate lyase and malate synthase


What enzyme is being targeted in the glyoxylate cycle to fight bacterial infections?

Isocitrate lyase


What are the reactions of the TCA cycle?

1. oxaloacetate
2. Citrate
3. Isocitrate
4. alpha-ketoglutarate
5. Succinyl Coa
6. Succinate
7. Fumarate
8. Malate


Describe the energy production by the TCA cycle wrt to NADH and FADH2
What is the total energy generated from one round?

NADH and FADH2 donate electrons to ETC and ATP produced via oxidative phosphorylation
NADH=>3ATP generated
FADH2=>2 ATP generated

12ATP total produced


What provides the primary link between glycolysis and TCA cycle? How does it do this?

PDH complex (nuclear-encoded Mt matrix complex) and acts by catalyzing the irreversible conversion of pyruvate into acetyl-CoA


The PDH complex is made of 3 enzymes and called E3 binding protein. What are these enzymes and what do they contain?

1. Pyruvate decarboxylase E1 that is phosphorylated containing TPP
2. Dihydrolipoyl transacetylase E2 w/ lipoic acid (arsenite inhibits)
3. Dihydrolipoyl dehydrogenase E3 contains NAD+ (ANCHORS E3 TO E2)


What are the sources of acetyl CoA?

1. pyruvate from glycolysis, amino acid degradation, fatty acid beta-oxidation, ketone body, ethanol metabolism


What is the initial rxn in the PDH complex?

decarboxylation of pyruvate by PDH through E1 through the cofactor TPP


Which portion of the PDH complex forms the acetyl CoA? What is released in this complex?

Lipoic acid released with 2 free sulfhydryls


What removes the electrons of the sylfhydryls? What is formed as a result in this complex?

E3 of dihyrdrolipoyl dehydrogenase
NADH and reoxidizes the lipoic acid to disulfide form


How many molecules of acetyl CoA and NADH are produced through the PDH complex?

1 molecule of both


Describe the first rxn of the TCA cycle and what type of step is it?

Acetyl CoA condenses w/ oxaloacetate (4C) to produce citrate (6C) via citrate synthase

irreversible step


T/F There is no acetyl CoA transporter to move acetyl CoA obtained from PDH rxn into the cytosol



Why is there a need for acetyl CoA in the cytosol? How was this accomplished?

-fatty acid synthesis
-export citrate via a citrate carrier


How is acetyl CoA moved out of the mitochondrion?

ATP citrate lyase cleaves the citrate to reform OAA and acetyl CoA


What is the relationship of citrate to amino acids?

citrate makes alpha ketoglutarate via the isocitrate dehyrdrogenase enzyme (rate determining enzymes) and alpha ketoglutarate is a precursor for making AA


Describe the 2 pathways that make up the TCA cycle

1. acetyl CoA plus OAA to make alpha ketoglutarate and 2 NADH

2. OAA makes succinyl CoA required for heme biosynthesis


What enzyme allows the 2 pathways to combine for the cycle?

alpha ketoglutarate dehydrogenase


T/F The cycle is catalytic bc it regenerates itself



If you have all the enzymes present with present lots of acetyl CoA and NAD+, what will occur?

nothing will happen


If you have all the enzymes present with present lots of acetyl CoA and NAD+ and small amount of intermediate, what will happen? Why?

all the pyruvate will be ocnverted to CO2 and NADH

intermediate gets converted to OAA then reacts with Acetyl CoA


Why can sugar not be made from fat?

there is no gain of carbon because the carbons are from OAA


Describe the step in the cycle of succinyl CoA synthetase. What is the energy used? What type of rxn is this?

Enzyme uses the energy from CoA hydrolysis to make GTP and converted to ATP by nucleoside diphosphate kinase

substrate level phosphorylation


What is the difference between substrate level phosphorylation and oxidative phosphorylation

SLP:energy to make high energy phosphate bond comes from rxn of the substrate

OP: energy comes from a proton gradient


Through what rxn are electrons removed and transferred to FADH2? What is unusual about this enzyme?

Oxidation of succinate to fumarate via succinate dehydrogenase

succinate dehydrogenase is membrane bound and member of ETC of complex 2


In the ETC, how is FADH2 pass?

FADH2 passes the electrons along 3 successive iron sulfur clusters and then on to ubiquinone (Coenzyme Q)


Wrt to the the TCA cycle, what will occur if you eat a large CHO meal?

-pyruvate made from glucose and send it to TCA cycle as acetyl CoA
-body will save it as fat and acetyl CoA for biosynthesis of fat


Why is fatty acid biosynthesis a drain on the TCA cycle?

removes citrate


How can the cycle be filled up if it is depleted? (3)

-most important rxn is pyruvate decarboxylase that is activated by acetyl CoA so some pyruvate is converted to OAA to supply substrate for citrate synthase
-breakdown of AA
- PEP formed from phosphoenol pyruvate carboxykinase then conversion to pyruvate to enter the TCA cycle


What are the 2 main functions of the TCA cycle?

1. supply electrons to the ETC in form of NADH and FADH2
2. supply metabolic precursors for biosynthesis


Pyruvate can go either way in the TCA cycle. Describe them and what regulates them

1. generation of NADH to be made into acetyl CoA
2. replenishes intermediates depleted by biosynthesis it can be converted to oxaloacetate

Both pathways are regulated by levels of acetyl CoA


If acetyl CoA levels are high, OAA is needed. How can this be done?

Pyruvate carboxylase is stimulated and PDH complex is inhibited
=> cuases shift from acetyl CoA to OAA


How is the PDH complex regulated? (4)

1. Acetyl CoA
2. ATP and NADH
3. PDH kinase=>activated by high ATP/ADP rations and high NADH/NAD+ ratios and by high acetyl CoA
4. PDH phosphorylation of pyruvate decarboxylase enzyme inhibits whole complex


How is citrate synthase regulated?

inhibited high ATP/ADP ratios and high NADH/NAD+ ratios


What regulates isocitrate DH?

inhibited by high ATP and NADH and is stimulated by high NAD+ and ADP and isocitrate


What enzyme affects citrate concentration in the mitochondria and cytosol?

isocitrate dehydrogenase


What is key for determining a cells metabolic direction?

CITRATE is inhibitory to glycolysis and stimulatory to fatty acid biosynthesis so citrate concentration will determine it


What can alpha KG be converted to via alpha KG DH?

glutamate for use in AA biosynthesis and protein synthesis


If NADH is high, what is the effect of alpha KG DH? What else is affected?

-enzyme is inhibited and alpha KG is diverted to glutamate
-succinyl CoA is inhibited


Describe the glyoxylate cycle and what is the result?

-isocitrate lyase cleaves isocitrate to make succinate and glyoxylate
-formation of CHO from acetyl CoA


What benefit could drugs targeted at the isocitrate lyase in the glyoxylate cycle have?

inhibit isocitrate lyase to not allow the organism to form CHO from acetyl CoA which will disrupt fatty acids broken down to acetyl CoA


What is the supercomplex?

The supercomplex is a dimer of Complex 1 complex 3 and complex 4 that bind these complexes and make electron transport more effective.