Week 9 - Unit 2 Flashcards
Intermediates of the TCA cycle are used for :
- heme synthesis
- Gluconeogenesis
- Fatty acid synthesis
- AA synthesis
One turn of the TCA cycle makes:
1- GTP
3- NADH
1- FADH2
What are the 4 things that can all generate acetyl CoA for the TCA cycle?
- fatty acid- palmitate
- ketone body- acetoacetate
- pyruvate
- Ethanol
Fatty acids and keytone bodies are ______ to acetyl-CoA
oxidized
AA _____ can be converted to pyruvate and then oxidized to Acetyl-CoA
Alanine
What enzyme converts pyruvate to acetyl-CoA at the end of glycolysis
Pyruvate dehydrogenase complex
True or false:
conversion of pyruvate to acetyl-CoA will transfer a H to NAD to make NADH (first in TCA pathway)
True
What are the inhibitors of pyruvate dehydrogenase?
- NADH (its own byproduct)
2. Acetyl-CoA (product)
What are the activators of Pyruvate Dehydrogenase ?
Calcium
ADP
The Pyruvate Dehydrogenase complex is part of the family of _____ ____ -_______
Alpha-keto-acid dehydrogenases
What are the three main a-keto acid dehydrogenases associated with TCA cycle ?
- Pyruvate Dehydrogenase
- Alpha Keto-glutarate dehydrogenase
- Branched chain AA dehydrogenase (MSUD)
What are the three subunits of of the Pyruvate dehydrogenase complex and what do they bind?
- E1= binds TPP
- E2= binds lipoate
- E3 = binds FAD
What is the E1 subunit on pyruvate dehydrogenase called?
Pyruvate decarboxylase subunit
-binds Thyamine Pyrophosphate (2 P groups )
What is the E2 subunit on pyruvate dehydrogenase called?
Transcylase subunit
-binds lipoate
What is the E3 subunit called on the pyruvate dehydrogenase called?
Dihydrolipoyl dehydrogenase
-binds FAD
What is the bond called that is created when pyruvate is converted to Acetyl CoA ?
High energy Thioester bond
O=C~SCoA
When you convert Pyruvate to Acetyl CoA what 2 things are created as byproducts?
NAD to NADH
CoASH to CO2
The creation of the high energy thioester bond of Acetyl CoA is coupled with what?
Reduction of NAD to NADH
In step one of Pyruvate to Acetyl CoA, what occurs?
Pyruvate loses CO2 when A-keto acid DH acts on it and takes the acetyl group
What is step oneafter the CO2 is lost from pyruvate?
Remaining 2 carbons are covalently bonded to Thyamine Pyrophosphate
-done by PDH
What is step 2 after TPP is bound to Pyruvate that lost CO2
Requires lipomide
-2 Carbon unit is transfered and attaches to lipoic acid
What happens after the 2 carbon unit (acetyl group) is transferred from the E1 unit with TPP (alpha-keto acid DH) to the E2 group of lipoic acid ?
- Acetyl group attached to thioester in Lipoic acid ( attached to trans Ac enzyme)
- -TPP regenerated for use again in step 1
3.Dihydrolipoyl transacetylase intermediate formed
What is step 3 after the
Dihydrolipoyl transacetylase is formed?
Acetyl is attached to CoA group to make Acetyl-CoA (still high energy thioester bond)
PDH is used again to attach the acetyl to CoA
What happens after the Acetyl-CoA is formed to the Transacetylase enzyme ?
Oxidized by FAD
-FAD is reduced to FADH2 which is then simultaneously oxidized by NAD as soon as FADH2 is made
How does the NADH gets it H from the pyruvate dehydrogenase complex?
it oxidizes FADH2 after FAD has oxidized TransAcetylase enzyme back into the cycle for lipoic acid usage
The Pyruvate Dehydration complex can be regulated through what two main ways?
- Covalent modification (phosphorylation will make it inactive)
- Allosteric regulation
What is the enzyme that requires coenzyme FAD to oxidize lipoic acid for use again in the cycle?
Dihydrolipoyl Dehydrogenase
Pyruvate Dehydrogenase complex is _____ when dephosphorylated in fed state.
active
Pyruvate Dehydrogenase complex is inactivated when it is phosphorylated by what?
PDH Kinase
When is the Pyruvate Dehydrogenase Kinase (PDH kinase) active to inactivate the PDH?
Levels of Acetyl CoA or NADH are high
When is PDH kinase inhibited (not able to inactive Pyruvate Dehydrogenase)?
High levels of :
ADP
Pyruvate
What 2 things at high levels can allosterically inactivate the Pyruvate Dehydrogenase complex while at the same time allosterically activate the PDH kinase?
Acetyl CoA
NADH
What two things will allosterically activate the Pyruvate Dehydrogenase Complex?
Pyruvate
NAD+
what does Pyruvate Dehydrogenase complex Phosphatase do ? who can activate the phosphatase?
removes the Phosphate from PDC to activate it
-insulin can activate the phosphatase
What can allosterically activate the Phosphatase to make PDC active by removing the phosphorlyation ?
High Calclium levels
released during exercise
Where is the Pyruvate Dehydrogenase Complex?
mitochondrial membrane
Arsenic poisoning inhibits what two things?
Pyruvate Dehydrogenase complex and the ETC
What are the products of the TCA cycle?
2 -CO2 1- CoASH 3- NADH 1- FAD(2H) 1- GTP
Where does the TCA cycle occur?
In mitochondria
What is the first intermediate created in TCA? what is its enzyme?
Citrate
Citrate synthase
What does the Citrate synthase do ?
Adds the Acetyl group from Acetyl-CoA to Oxaloacetate to make Citrate
What type of reaction does Citrate synthase cause?
Condensation reaction to combine oxaloacetate and acetyl-coA
Where does the energy for the reaction that Citrate synthase causes come from?
the Thioester bond between CoASH and Acetyl - CoASH is released
What is the second step intermediate created in TCA (after citrate)?
Aconitase will cause an isomerization reaction converting Citrate into Isocitrate
What is the name of the second intermediate after Citrate?
Isocitrate
The Aconitase facilitates _______ followed by _____ that results in bond rearrangement to form Isocitrate.
dehydration
rehydration
Aconitase requires ______ to be active
Iron
What is the third step intermediate:
Isocitrate is converted to ?
Alpha-ketoglutarate
first decarboxylation step where CO2 is released
what enzyme will facilitate the decarboxylation of Isocitrate to Alpha-ketoglutarate?
Isocitrate Dehydrogenase
first major decarboxylation step in TCA
Isocitrate Dehydrogenase requires ______ as a cofactor.
Magnesium
What is the first regulated step in TCA cycle?
activity of Isocitrate dehydrogenase
What is the 4th intermediate of the TCA cycle after alpha-ketoglutarate ?
Succinyl Co-A
What enzyme will change alpha-ketoglutarate into Succinyl Co-A?
Alpha-keto glutarate dehydrogenase
In the activity of Alpha-keto glutarate dehydrogenase, what occurs?
NAD is Reduced to NADH
CoASH is added to make Succinyl CoA
CO2 is released
(oxidative carboxylation reaction)
What two things occur when Isocitrate dehydrogenase acts on Isocitrate to make Alpha-keto glutarate?
CO2 is release
NAD is reduced to NADH
True or false:
Succinyl CoA has a high energy thioester bond
true - CoASH was added by Alpha-keto glutarate dehydrogenase
Where does the energy to make GTP from addition of free phosphate to GDP come from ?
cleavage of high energy thioester bond on Succinyl coA and r
What enzyme will convert Succinyl-CoA to Succinate and add a P to GDP?
Succinyl thiokinase
What is Succinate converted to in the TCA cycle?
Fumarate
What is the enzyme that converts Succinate to Fumarate?
Succinate Dehydrogenase
Succinate Dehydrogenase is also _______ of the ETC.
Complex 2 of the ETC
What will succinate Dehydrogenase do for the ETC as it converts succinate to fumarate for the TCA cycle?
reduce FAD to FADH2 for immediate use in the ETC as complex 2
What will fumarate be converted to ?
Malate
What will Malate be converted to in the TCA?
Oxaloacetate (high delta G (29.7) - needs energy to happen)
What enzyme will convert Fumarate to Malate?
Fumarase (will cause hydration across double bond to make malate)
What is the last step to make an NADH?
Enzyme Malate dehydrogenase reacting with Malate to make Oxaloacetate
Why is the reaction that converts Malate to Oxaloacetate able to move forward when it has such a high delta G?
Oxaloacetate is kept at a reduced level in mitochondria
- an intermediate for other pathways
- will be used up all the time so the forces driving to equilibrium will allow reaction to occur
What are the three steps that are regulated in TCA cycle the way that Pyruvate dehydrogenase is regulated ?
- Isocitrate dehydrogenase
- Alpha-keto glutarate dehydrogenase
- Malate dehydrogenase
The oxidation reactions that convert pyruvate to CO2 are specifically catalyzed by _____ enzymes.
Dehydrogenases
What will Citrate synthase be inhibited by ?
elevated levels of citrate
What will high levels of ADP enhance in the TCA cycle?
Isocitrate Dehydrogenase activity
What will High levels of NADH inhibit in the TCA cycle?
Isocitrate dehydrogenase
A-ketoglutarate dehydrogenase
Malate dehydrogenase
WHat will high levels of Calcium enhance activity of in the TCA cycle?
Isocitrate dehydrogenase
Alpha-ketoglutarate dehydrogenase
ADP is a signal of ____ energy in the cell.
low
What other pathways does the TCA cycle play an important role in by creating intermediates for those pathways?
- Fatty acid synthesis
- AA synthesis
- Heme synthesis
- Gluconeogenesis
What intermediate of TCA will contribute to Fatty acid synthesis?
Citrate
What intermediate of TCA will contribute to AA precursors for Neurotransmitters through AA synthesis?
Alpha-ketoglutarate
What intermediate of TCA will be used in Heme synthesis?
Succinyl CoA
What intermediate of TCA will be used in Gluconeogenesis?
Malate
What intermediates of TCA will be used for AA synthesis
Alpha-ketoglutarate
Oxaloacetate
As intermediates are being pulled out of the TCA cycle for other reactions, _______ reactions will refill the intermediates for TCA usage.
Anapleurotic (anapleurosis)
What is the anapleurotic reaction that will refill oxaloacetate?
Pyruvate carboxylase will change it back to Oxaloacetate
adds CO2 and uses ATP energy
What does Pyruvate Carboxylase require as a cofactor to convert Pyruvate back to Oxaloacetate ?
Biotin (vitamin H)
Biotin will bind CO2 as an intermediate and the activated CO2 is added to Pyruvate to form the carboxyl group of ______.
Oxaloacetate
What is an allosteric activator of Pyruvate carboxylase?
Acetyl CoA
IN the second anapleurotic reaction, Glutamate can be transaminated to _______ for the TCA cycle.
alpha-ketoglutarate
What enzyme will change Glutamate to alpha-ketoglutarate
Glutamate dehydrogenase
direction of reaction will depend on cellular needs, easily reversible
Valine and Isoleucine metabolism (BCAA) will eventually be converted into ______ that will be an anapleurotic reaction to refill _____.
Proprionyl Co-A
Succinyl CoA
______ can be deaminated and refill oxaloacetate in the TCA cycle
Aspartate
What are the main intermediates that are refilled in TCA cycle?
Oxaloacetate
Alpha-ketoGlutarate
Succinyl CoA
Fumarate (from AA)
What are the two major anapleurotic reactions in TCA?
Pyruvate Carboxylase making Oxaloacetate
BCAA metabolized to make Succinyl CoA
LDH will ______ pyruvate in combination with the coenzyme NADH which will be ______ in the reaction.
Reduce
Oxidize (lose its H)
Decreased oxidation of NADH or FADH in ETC will result in _______ conversion of Pyruvate to Lactic Acid.
Increased
High levels of NADH will regulate the TCA cycle by inhibiting the action of ________, _______, ______.
Isocitrate dehydrogenase
Alpha-ketoglutarate dehydrogenase
Malate dehydrogenase
In ischemia (or inhibtor to ETS), the NADH will become elevated, and then the TCA will in result be inhibited due to _______ at increasing levels. The individual can then present with lactic acidosis.
NADH
Inbetween what two intermediates is FAD reduced to FADH2 in TCA cycle? by what enzyme ?
Succinate to Fumarate
Succinate dehydrogenase
What is an inhibitor of citrate synthase, isocitrate dehydrogenase, and alpha-ketoglutarate dehydrogenase ?
NADH
Pyruvate dehydrogenase is an ____ linked trait.
X linked
In pyruvate dehydrogenase deficiency , the venus lactate levels will remain ______ during fasted and fed states, and especially high after fed state.
High
greatly increased after meal of carbohydrates
Many of the cofactors required for TCA cycle include:
TTP
FAD
Coenzyme A (CoASH)
One molecule of Heme requires 8 ______ and 8 ________.
Glycine
Succinyl-CoA (comes primarily from TCA cycle)
Heme is required for transport of oxygen in blood and what other process?
ETS - cytochrome oxidase, and many reducing reactions in ETS
In the structure of Heme, there are 4 ______ rings joined by _____ bridges.
Pyrrole rings
Methenyl bridges
Side chains of Heme on the rings can consist of what 4 groups that will be ordered to identify the type of heme?
- Acetyl
- Propionyl
- Methyl
- Vinyl
(ex: MVMVMPPM)
What is the most common type of Heme?
What is the sequence?
Type III heme
MVMVMPPM
8 R groups - 1 for each pyrrole ring
Synthesis of Heme starts with what two molecules?
Succinyl CoA and Glycine
Heme synthesis pathway is regulated by feedback inhibition, meaning?
Heme can inhibit is own synthesis
only one regulatory step in pathway
What is the name for the Enzyme that Heme will regulate its own synthesis through feedback inhibition that is blocked called?
Alpha-aminolevulinic synthase
What is the final step in the heme synthesis?
Integrating the Fe (iron) into the Heme molecule ring - needed to funciton
Glycine and Succinyl CoA will combine to make what in Heme synthesis ?
Alpha-Aminolevulinic acid
What is released during the reaction caused by Alpha-aminolevulinic acid using Glycine and succinyl co-A as substrates?
CoASH and CO2
What cofactor is required for the condesation of glycine with succinyl coA in heme synthesis ?
PLP (Pyridoxal phosphate) - B6
In second step of heme synthesis you need 2 molecules of _________. It is a dehydration reaction where ___ molecules of water are released.
Alpha-Aminolevulinic acid (a-ALA)
2
What is the enzyme that will combine two molecules of a-ALA through dehydration to form Porphobilinogen (a pyrrole ring)?
a-ALA dehydratase
a-ALA dehydratase is not regulated but what can inhibit it?
Lead (high levels)
- stops heme synthesis
The _______ are a series of diseases caused by deficiencies in the Heme synthesis pathway.
Porphyrias
- can present with any number of presentations
Which reactions are irreversible in the TCA cycle?
- Isocitrate to a-ketoglutarate
- a-ketoglutarate to Succinyl Co-A
- Oxaloacetate+ Acetyl CoA to Citrate
Which TCA intermediates have 6 carbons
Citrate
Isocitrate
Which TCA intermediates have 5 Carbon
only Alpha-ketoglutarate
Which TCA intermediates have 4 Carbons ?
Succinyl CoA Succinate Fumarate Malate Oxaloacetate
Which TCA reactions have very strongly negative Delta G nots ?
- Acetyl CoA to Citrate
- Isocitrate to Alpha-keotglutarate
- Alpha-ketoglutarate to Succinyl CoA
The reactions catalyzed by aconitase and malate dehydrogenase have ______ Delta G nots and are thermodynamically and kinetically _____.
positive
reversible
Because _______ is rapid in both directions, equilibrium values for the concentration ratio of products to substrates is maintained, and the concentration of citrate is about ____ times that of isocitrate.
aconitase
20
The accumulation of citrate instead of isocitrate facilitates transport of excess citrate to the cytosol where it can provide a source of acetyl-CoA for pathways such as ______ and ______.
Fatty acid synthesis
Cholesterol synthesis
The large accumulation of citrate as opposed to isocitrate in TCA allows citrate synthase to decrease activity when flux through ______ _____ is decreased.
isocitrate dehydrogenase
The malate is kept in a very large concentration compared to oxaloacetate (similar to citrate vs isocitrate funciton) so that in the liver during fasting, there is a net flux towards malate , so it can then be transported out of the mitochondria to provide a substrate for _______.
gluconeogenesis
True or false:
Citrate synthase has no allosteric regulators
True - it is only regulated by the levels of citrate and avaliability of oxaloacetate
At the concentration of isocitrate found in the matrix a small change in the concentration of ____ and _____can produce a large change in the rate of the isocitrate dehydrogenase reaction.
ADP (if avaliable increases rate)
NAD+(activator)
NADH (inhibitor)
ALLOSTERIC- powerful regulation
The Km shifts to a much lower value for isocitrate dehydrogenase when ____ is avaliable as all of the subunits of the enzyme are in their active conformation.
ADP
The alpha-ketoglutarate dehydrogenase complex, although not an allosteric enzyme, is product inhibited by what 3 things?
NADH
Succinyl-CoA (product)
GTP
(ADP indirectly if increased due to lack of NADH oxidation in ETS as it leads to NADH increase)
In the liver, a decreased rate of isocitrate dehydrogenase will _____ citrate concentration, which stimulates citrate efflux to the cytosol .
increase
In the brain , alpha-ketoglutarate intermediate is converted to ______ and then to ______ (GABA) as a neurotransmitter.
Glutamate
Gamma-aminobutyric acid (GABA)
In skeletal muscle, Alpha-ketoglutarate is converted to _____, which is transported through the blood to other tissues.
Glutamine
What does pyruvate carboxylase function as ?
major anaplerotic enzyme - catalyzes addition of CO2 to pyruvate to form oxaloacetate
-contains Biotin
What does the pyruvate carboxylase interaction require to form oxaloacetate from pyruvate ?
Biotin
ATP and Magnesium
(forms carboxyl group by adding CO2 to pyruvate)
As the concentration of oxaloacetate is depleted through the efflux of TCA cycle intermediates, the rate of the citrate synthase reaction decreases and acetyl-coA rises. Acetyl-CoA then activates _______ to synthesize more ______.
Pyruvate carboxylase
Oxaloacetate
Alanine and Serine carbons can enter through _____ _____.
Pyruvate carboxylase
In all tissues with mitochondria (except liver), oxidation of the two BCAA ____ and _____ to ______ forms a major anaplerotic route.
Isoleucine
Valine
Succinyl Co-A
In the liver, other compounds (than isoleucine and valine) like methionine, threonine, and odd-chain-length or branched fatty acids also enter TCA cycle as ______.
Succinyl CoA
In most tissues, glutamine is taken up fro the blood, converted to _____, then oxidized to ______, forming another major anaplerotic route.
glutamate
alpha-ketoglutarate
TCA cycle can not be resupplied with intermdiates by ________ or ______ which forms only acetyl CoA.
even-chain-length fatty acid oxidation
ketone body oxidation
In TCA cycle, two carbons are lost from citrate before _____ is formed, so there is no net conversion of _______ carbon to oxaloacetate.
Succinyl-CoA
Acetyl (carbon)
Vitamin ____ deficiency reduces the activity of pyruvate dehydrogenase and the TCA cycle, severely restricting ATP generation.
B1 (Thiamine - used as Thiamine pyrophosphate in pyruvate dehydrogenase reaction to make Acetyl-coA)
