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40 Cards in this Set

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Which enzyme catalyzes the first reaction in glycolysis?
hexokinase
What gets turned into what in the first reaction in glycolysis?
glucose gets turned into glucose-6-phosphate (G6P)
Kinase
is an enzyme that transfers phosphoryl groups between ATP and a metabolite

(the metabolite that serves as the phosphoryl group acceptor is indicated in the prefix of the kinase name
Is hexokinase a specific enzyme?
No, it is a nonspecific one because it will also catalyze the phosphorylation of hexoses like D-glucose, D-manose, and D-fructose
Name one isozyme from hexokinase?
glucokinase which is found in the liver
What is the second substrate for hexokinase?
Mg2+-ATP complex
Is uncomplexed ATP a potent competitive inhibitor for of hexokinase?
Yes, because without the Mg2+ shielding the negative charges of the ATP's alpha and beta or alpha and gamma-phosphate oxygen atoms, the nucleophilic attack of the C6-OH group of glucose is more difficult
Does glucose induce a large conformational change in hexokinase?
Yes, the two lobes tha tform its active site cleft swing together by up to 8 A engulfing the glucose like the closing of jaws
What would happen if the catalytic and reacting groups were in the poper position for reaction while the enzyme was in the open position?
ATP hydrolysis: phosphoryl group transfer to water would be thermodynamically favored
What is responsible for the hexokinase's specificity?
substrate-induced conformational change and the active site polarity being reduced by the exclusion of water (expediating nucleophilic rxn)
What do you call the enzyme that catalyzes the second rxn?
phosphoglucose isomerase
Phosphoglucose isomerase catalyzes what to what?
G6P to fructose-6-phosphate (F6P)
What type reaction does phosphoglucose isomerase catalyze?
an isomerization rxn of an aldose to a ketose
In what form do G6P and F6P predominate?
cylic
What are the primary steps in the reaction that phosphoglucose isomerase catalyzes?
1. Ring opening
2. Isomerization
3. Ring closure
What type of catalysis does phosphoglucose isomerase perform?
acid-base
What is special about the alpha proton on a carbonyl group?
it is acidic
In the second rxn in glycolysis how is the cis-enediolate intermediate formed?
a base abstracts the acidic proton from C2 to form the intermediate
In the second rxn in glycolysis which proton is replaced in the overall proton transfer?
proton on C1
What enzyme catalyzes the third rxn in glycolysis?
Phosphofructokinase (PFK)
Phosphofructokinase catalyzes what to what?
Fructose-6-phosphate (F6P) to Fructose-1,6-biphosphate (FBP)
Why is this a biphosphate and not a diphosphate?
Because the 2 phosphate groups are not attatched to one another
Which rxn is the PFK reaction similar to?
hexokinase rxn because the enzyme catalyzes the nucleophilic attack by the C1-OH group of F6P on the electrophilic gamma-phosphorus atom of the Mg2+-ATP complex
Why does phophofructokinase play a central role in control of glycolysis?
because it catlyzes one of the pathway's rate-determining reactions
What can enhance the activity of PFK and what can inhibit the activity of PFK allosterically?
PFK can be enhanced by AMP and inhibited allosterically by ATP and citrate
Which enzyme catalyzes the fourth step in glycolysis?
aldolase
Aldolase catalyzes what to what?
it cleaves fructose-1,6-biphosphate to form 2 trioses glyceraldehyde-3-phosphate (GAP) and dihydroxyacetone phosphate (DHAP)
In the fourth rxn in glycolysis atoms 123 of glucose become what?
321 of DHAP (has carbonyl in center)
In the fourth rxn in glycolysis atoms 456 of glucose become what?
123 of GAP (with carbonyl on outside starting with 1)
What type of reaction is reaction 4 of glycolysis?
aldol cleavage (retro aldol condensation)
What stabilizes the enolate?
resonance, as a result of the electron-withdrawing character of the carbonyl oxygen atom
What catalyzes aldol cleavage?
stabilizing the enolate intermediate through increased electron delocalization
What type of mechanism does a nonenzyme catalyzed enol rxn use?
base catalysis
The aldol cleavage between C3 and C4 of FBP requires a what, and where?
a carbonyl at C2 and a hydroxyl at C4
Aldol cleavage of G6P yields what types of products?
products of unequal carbon chain length
Aldol cleavage of FBP results in what?
two interconvertible C3 compounds that can therefore enter a common degradative pathway
What is a Schiff base?
an imine that forms between an amine and an aldehyde or ketone
Which enzyme catalyzes reaction five of glycolysis (which is the final stage of part one)?
Triose phosphate isomerase
What type of isomers are DHAP and GAP? Or F6P and G6P?
ketose-aldose isomers
Does GAP or DHAP continue in the glycolytic pathway?
GAP