Glycolysis - Substrate and Product structures and enzymes Flashcards
Write down the names of the substrates and products of each reaction of glycolysis.
glucose - (hexokinase) - glucose-6-phosphate - (phosphoglucose isomerase) - fructose-6-phosphate - (phosphofructokinase) - Fructose-1,6-biphosphate - (Aldolase) - GAP + DHAP - (Triose phosphate isomerase) - GAP * 2 - (Glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) - 1,3-biphosphoglycerate - (phosphoglycerate kinase) - 3-phosphoglycerate - (phosphoglycerate mutase) - 2-phosphoglycerate - (enolase) - phosphoenolpyruvate - (pyruvate kinase) - pyruvate
Write down the steps with the input/output of ATP, NADH, H2O and Mg2+/K+
Refer to page 474
Draw all the substrates and products of glycolysis.
Refer to page 474
Draw Glucose.
Refer to page 474
Draw G6P
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Draw F6P
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Draw FBP
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Draw GAP
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Draw DHAP
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Draw 1,3-BPG
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Draw 3PG
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Draw 2PG
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Draw PEP
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Draw pyruvate
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Which enzyme converts glucose to G6P?
hexokinase
Which enzyme converts G6P to F6P?
phosphoglucose isomerase
Which enzyme converts F6P to FBP?
phosphofructokinase
Which enzyme converts FBP to DHAP and GAP?
aldolase
Which enzyme converts DHAP to GAP?
triose phosphate isomerase
Which enzyme converts GAP to 1,3-BPG?
glyceraldehyde-3-phosphate dehydrogenase (GAPDH)
Which enzyme converts 1,3-BPG to 3PG?
phosphoglycerate kinase
Which enzyme converts 3PG to 2PG?
phosphoglycerate mutase
Which enzyme converts 2PG to PEP?
enolase
Which enzyme converts PEP to pyruvate?
Pyruvate kinase
Draw the mechanism for GADPH.
Refer to notes
Draw the mechanism for PGM.
Refer to notes.
Draw the mechanism for enolase.
Refer to notes
Draw the mechanism for alcoholic fermentation
Refer to notes
Draw the mechanism for homlactic fermentation.
Refer to notes
What type of reaction is the GAPDH reaction?
Nucleophilic attack - SN2
Oxidation reaction (Dehydrogenation)
Nucleophilic attack - SN2
What type of reaction is the alcoholic fermentation reaction using TPP?
SN1
What type of reaction is the alcoholic fermentation reaction with alcohol dehydrogenase?
Oxidation to reform NAD+.
What is the enzyme of reaction 1?
Hexokinase
What is the enzyme of reaction 2?
Phosphoglucose isomerase or phosphohexose isomerase
What is the enzyme of reaction 3?
Phosphofructokinase
What is the enzyme of reaction 4?
aldolase
What is the enzyme of reaction 5?
Triose phosphate isomerase
What is the enzyme of reaction 6?
glyceraldehyde-3-phosphate dehydrogenase
What is the enzyme of reaction 7?
Phosphoglycerate kinase
What is the enzyme of reaction 8?
Phosphoglycerate mutase
What is the enzyme of reaction 9?
enolase
What is the enzyme of reaction 10?
Pyruvate kinase
What is/are the substrates of reaction 1? (in the forward direction)
ATP-Mg2+ and glucose
What is the mechanism of reaction 1?
Proximity effects.
Two binding sites for ATP-Mg2+ and glucose. Upon binding, changes confirmation, bringing the substrates together to cause the reaction to occur instantaneously.
What is/are the inhibitor(s) of reaction 1?
Competitive inhibitor - ATP (uncomplexed) Allosteric inhibitor (G6P)
Reaction 1, in the forward direction is: exergonic or endergonic?
Exergonic
Do cancer cells upregulate or downregulate hexokinase?
upregulate
Under what conditions does uncomplexed ATP accumulate?
When energy is barely used and thus, ATP is plentiful. Mg2+ is no longer able to complex with all the ATP so glycolysis is interrupted and glycogen is made instead.
What is the substrate of reaction 2 in the forward direction?
G6P
What is the mechanism for reaction 2?
MG2+ is required!
Specific for G6P/F6P
What is the main control for this reaction (2) and, what can be inferred from this?
The main control is concentration. We can infer that this reaction is reversible and that delta G is nearly zero.
G6P is a(n) _____hexose whilst F6P is a(n) _____hexose.
aldohexose - G6P
ketohexose - F6P
What is the enzyme of reaction 3?
Phosphofructokinase-1
What is/are the substrate(s) of reaction 3 in the forward direction?
ATP-Mg2+ and F6P
How is this enzyme (PFK-1) controlled? What are its inhibitors/activators?
Important enzyme for regulation.
ATP and citrate are both inhibitors.
ATP is an allosteric inhibitor.
ADP, AMP and Fructose-2,6-biphosphate are allosteric activators.
What is adnylate kinase?
What occurs if ATP concentration is decreased?
If the kinase is active, what accumulates?
Enzyme that readily equilibrates 2 ADP into 1 ATP and 1 AMP.
Enzyme that is active when ATP levels are low and ADP levels are high.
K = [ATP][AMP]/[ADP]^2
Decreased ATP –> pushes reaction forward
If the kinase is active, AMP accumulates.
What are other features of this reaction (3)?
Commits the cell to glycolysis.
Very exergonic
What is/are the substrate(s) of reaction 4?
FBP
What is the mechanism of reaction 4?
Aldolase catalyzes the cleavage of FBP by aldol condensation mechanism.
Products of this reaction are depleted rapidly and this reaction is pulled forward by reactions 5 and 6.
How is reaction 4 pulled forward if it is endergonic?
Reactions 5 and 6 quickly deplete the products of this reaction, pulling it forward.
How is reaction 4 controlled?
concentration control
What is the mechanism for reaction 5?
Reversible reaction catalyzed by acid-based catalysis. His95 and Glu165 of the enzyme are involved.
How is reaction 5 controlled?
endergonic, pulled forward as product is used up.
What occurs if step 5 is blocked?
Glycolysis proceeds at half the rate.
What is the most important fact about reaction 6?
It’s the reaction responsible for the generation of energy in glycolysis as a whole.
Once again, reaction 6 is endergonic, how is it pulled foward?
Pulled forward by reaction 7.
1,3-BPG is very unstable.
In reaction 6, an _______ is converted to a _______ group.
aldehyde –> carboxyl
In reaction 6, oxidation of the aldehyde does two things. These are?
1 - Make a high-energy phosphate bond
2 - Produce a reduced moiety (NADH)
What is the oxidizing agent of this reaction? (6)
NAD+, which is reduced to NADH
What drives the formation of acylphosphate during reaction 6?
Free energy from the oxidation reaction.
What is the evidence supporting the GADPH reaction?
1 - Iodoacetate inhibits this reaction, indicating the involvement of a cysteine residue of the enzyme
2 - Tritium from GAP is trasnferred directly to NAD which indicates that the hydrogen transfer is under the form of a hydride ion
3 . Labelled ATP does not cause the product to be labelled. Pi is instead transferred providing evidence for the acyl enzyme intermediate.
What are the substrates for reaction 7?
1,3-BPG and ADP-Mg2+
What is the mechanism for reaction 7?
Proximity effect.
Coupled to reaction 6.
ATP is generated by substrate-level phosphorylation
Where does the energy for this reaction come from? What is one reason for 1,3-BPG being desperate to hydrolyze?
Energy for this reaction comes from the highly energetic 1,3-BPG.
3-PG is resonance hybridized.
In reaction 8, something is very rarely recorded in the mixture. What is it?
2,3-BPG
What is the enzyme for reaction 8 and what is important about it?
Phosphoglycerate mutase.
Phosphorylated His-179 residue.
Is the product of the forward reaction of step 8 stable or not?
2-PG is stable
What is the mechanism for reaction 9?
Dehydration of 2-PG.
1 - Rapid extraction of a proton at C-2 by a general base of the enzyme, generating a carbanion
b - abstracted proton easily exchanged with solvent
2 - Rate limiting elimination of OH
How do we know that the exchange in reaction 9 involves a proton?
Tritiated 2-PG will cause water to become labeled. Thus, the exchange does not involve a hydride ion.
What are the special requirements for reaction 10?
K+ and Mg2+ are required.
PEP is desperate to hydrolyze. True or false?
True, the reaction is very exergonic
What reactions are:
a) oxidation reaction
b) substrate-level phosphorylation
c) phosphorylations
d) isomerizations
e) dehydrations
f) carbon-carbon bond cleavage
a) 6
b) 7, 10
c) 1, 3, 7, 10
d) 2, 5
e) 9
f) 4
Is reaction 1 exergonic, endergonic or reversible?
exergonic
Is reaction 2 exergonic, endergonic or reversible?
Reversible
Is reaction 3 exergonic, endergonic or reversible?
Exergonic
Is reaction 4 exergonic, endergonic or reversible?
Endergonic
Is reaction 5 exergonic, endergonic or reversible?
Endergonic/reversible
Is reaction 6 exergonic, endergonic or reversible?
Endergonic
Is reaction 7 exergonic, endergonic or reversible?
Exergonic
Is reaction 8 exergonic, endergonic or reversible?
endergonic/reversible
Is reaction 9 exergonic, endergonic or reversible?
Endergonic
Is reaction 10 exergonic, endergonic or reversible?
Exergonic
