Krebs Flashcards
Main step in Krebs prep stage
c-c-c pyruvate has carbon removed by pyruvate dehydrogenase (PDH) becomes Acetyl coA
PDH
Pyruvate dehydrogenase-makes ccc pyruvate into cc Acetyl coA. Huge complex made up of three enzymes and five coenzymes. Has lipoic acid covalently bound.
First four steps in Krebs
Claisen condensation
Dehydration /rehydration
Oxidative decarboxylation
Oxidative decarboxylation
Claisen condensation, enzyme, and intermediate
*citrate synthase coverts methyl in Acetyl CoA to methylene in *citrate
Dehydration/rehydration
Aconitase repositions OH group in citrate to *cis Aconitate and *Isocitrate
Oxidative decarboxylation
Isocitrate dehydrogenase oxidizes OH to carbonyl, stabilizes carbanion *alpha ketoglutarate *succinyl coA
Last four steps in Krebs
Substrate level phosphorylation
Dehydrogenation
Hydration
Dehydrogenation
Substrate level phosphorylation
Succinyl CoA synthetase hydrolyzes succinyl CoA to succinate. Thioester leads to high energy phosphate bond, negative G. GTP/ATP
Dehydrogenation 1
Succinate dehydrogenase introduces double bond in center create fumarate
Hydration
Fumarase adds water, removes double bond in fumarate creates malate
Dehydrogenation 2
Malate dehydrogenase generates carbonyl creates OAA (oxaloacetate)
Products of Krebs (prep included)
2 NADH prep
6 NADH
2 ATP
2 FADH
Products from glycolysis and Krebs
4 ATP
10 NADH
2 FADH
Ready for ETC
Three irreversible steps in Krebs
Claisen comdensation, and both oxidative decarboxylations
Aconitase
Enzyme used in dehydration/rehydration
FeS center
Cysteine residues bind to Fe
If Fe low uptake increased and storage deceased
Vertebrates cannot…
Convert Acetyl coA to carbs(or fatty acids to carbs)
Glyoxylaye cycle
Bypass that allows microbes and invertebrates to convert to carbs (done by plants)
Enzymes unique to glyoxylaye
Isocitrate lyase and malate synthase
What are the three stages in Krebs
Acetyl coA production
Acetyl coA oxidation
ETC/oxidative phosphorylation
OAA uniformly labeled is condensed with Acetyl coA, how much radioactivity in OAA after one cycle
1/2
Acetyl coA labeled reacts with unlabeled OAA how many on OAA after one cycle
All
Two CO2 produced in first cycle Krebs have their origin from
Two carboxyl groups from OAA
Which enzymes are irreversible
Citrate synthase
Isocitrate dehydrogenase
a ketoglutarate dehydrogenase
How many electrons from Krebs will enter ETC
20
How many NADH can convert 4FE 4S to a fully reduced state
2
How many intermediates in Krebs can be trannaminated to amino acids
Three
Which intermediates and what amino acids
Pyruvate to alanine
OAA to aspartate
A ketoglutarate to glutamate
Krebs only operates when O2 is present because
O2 accepts electrons from ETC
Subsequent step after removing CO2 and attaching Acetyl group
Reduction of lipoic acid
When does Krebs directly yield reducing owner NADH or FADH
Succinate to fumarate by succinate dehydrogenase
If succinyl coA is labeled at C1 where in fumarate
Equally in C1 and C4
What would slow or stop Krebs
High ATP and high NADH
What intermediate does the glyoxylate cycle pass
Succinate
Why is Claisen condensation irreversible
The standard free energy is so negative
The iron in FeS clusters participate in rxns by
Gaining or losing electrons
Intermediates in Krebs at used in a one step biosynthesis of
Amino acids
Which intermediate is not removed by another metabolic pathway
Isocitrate
