METABOLISM SYLLABUS 3: Fates of Pyruvate Flashcards Preview

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Flashcards in METABOLISM SYLLABUS 3: Fates of Pyruvate Deck (26)
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what can happen to pryuvate from glycolysis?

1) reduced to LACTATE via LDH in RBC, exercising muscle, embryonic tissue = ANAEROBIC GLYCOLYSIS

2) enter MITO for further metabolism by PDH to ACETYL CoA = AEROBIC GLYCOLYSIS



what does LDH reaction catalyze





why is LDH reaction important in RBC?

critical to RBC here b/c NADH reodixidzed back to NAD+, which is needed for glycolysis to continue at the G3PDH step 



what do tissues w/ mito do with the LDH reaction?

oxidize the NAD+ from the LDH reaction to NADH after it is transported into the mito by the respiratory chain


how is LDH reaction improtant in muscle contraction?

reoxidizes NADH whenever glycolysis is very rapid - so when muscle contraction, high insulin levels, tumor cells


what is ANAEROBIC glucolysis?

glycolysis without oxygen 

when lactate is the final product of glycolysis, and net of glycolysis is : 

glucose + 2ADP + Pi -> 2 Lactic Acid + 2 ATP




what happens to lactate produced from LDH?

1) high levels of lactic acid leaves the RBC/muscle/tissue where it was produced, -> blood

high levels of lactate in blood alter blood pH, cause cramps, aggravate gout 

2) other lactate enters tissues -> reoxidized back to pyruvate -> undergoes PDH reaction for energy production or can be converted to glucose in liver during gluconeogenesis 


how does the RBC or brain or heart know which direction to go w/ the LDH reaction?

this question is b/c the LDH reaction is reversible

LDH is a tetramer made of 2H and 2M subunits;

therefore have 5 different isozymes/isoforms, 

H4, H3M, H2M2, HM3, M4




where are the H vs. M isoforms of LDH found? 

what are their properties?

H isoforms: brain, heart; have higher affinity for lactate and NAD; inhibited by high levels of pyruvate


M isoforms: RBC, skeletal muscle; have lower affinity for lactate and NAD; not inhibited by high levels of pyruvate


what happens to pyruvate in yeast cells?

it is converted to ethanol (alcohol) by pyrvuate decarboxylase 



describe the pyruvate decarboxylase reaction

how pryvuate -> alcohol in yeast cells 

pyruvate + TPP -> CO2 + acedylaldehyde, by pyruvate decarboxylase 

acetylaldehyde + NADH -> ethanol + NAD, by alcohol DH 


NET: glucose -> 2 ethanol + 2CO2 + 2ATP


what are mammals lacking re: alcohol fermentation rxn?

mammals do not have yeast pyruvate decarboxylase 

thus mammals oxidize ethanol back to acetylaldehyde by alcohol DH, but that becomes acetyl CoA 

otherwise, if we had pyruvate decarboxylase, glucose -> ethanol, as yeast do


what happens to pyruvate in most tissues?

undergoes the PDH reaction, converting it to acetyl COA 

acetyl CoA can be further oxidized in the TCA cycle, generating NADH and FADH2 for energy production by the respiratory chain 



what is the naure of the PDH rxn?



where does PDH reaction occur?

mito matrix


what is the net of the PDH reaction?

pryuvate + CoASH + NAD -> acetyl CoA + CO2 + NAHD + H


what does CoASH do?

carries acyl groups like acetyl and fatty acyl groups 

contains B vitamin phosphopantethiene and an SH group at its terminus by which acyl groups attach


what are the enzymes of the PDH complex?

vitamin cofactors?

enzymes: E1, E2, E3, PDH kinase, phosphatase 

vitamin cofactors: TPP for E1, lipoic acid for E2, riboflavin for E3, phosphopantetheine for CoASH, niacin for NAD+


describe the PDH mechanism

1) E1 decarboxylates pyruvate and replaces the CO2 w/ TPP

2) E2 replaces the TPP group w/ lipoamide. Then CoA is added to the reduced lipoamide 

3) E3 reduces FAD, regenerating the lipoamide so that E2 is functional again - this matters so that acetyl CoA  can keep being produced 



what inhibits each step of the PDH mechanism? (metabolites)

ATP inhibits E1

Acetyl CoA inhibits E2 

NADH inhibits E3 

aka each of the reaction's products inhibits that reaction, and these are all signs of high energy


what hormonally controls the PDH reaction?

PDH Kinase: INHIBITS E1 by phosphorylating it; not effected by glucagon or epinephrine 

INSULIN stimulates/increases PDH phosphatase: activates E1





what is unique about what happens in the E3 reaction of PDH?

reoxidation of FADH2 by NADH is the only case in metabolism in which FADH2 reduces HAD+ to NADH; usually, NADH reduces FAD to FADH2


what happens to C3, 4 of the original glucose?

comes off as CO2 in the PDH reaction


what happens to C1, 6 of the original glucose from glycolysis?

form the CH3 of acetyl CoA in PDH


what happens to carbons 2, 5 of the original glucose?

form the C=O of the acetyl group of PDH reaction

come off as CO2 in the TCA cycle


is PDH kinase sensitive to glucagon, epi?


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