Glycolysis Flashcards by Debon Lee

What are the 2 “stages” of glycolysis and their purpose?

Preperative stage & Payoff stage

Preparative - Trap and destabilize glucose, and cleavage of phophofructose by investing ATP

Payoff - ATP, NADH, and pyruvate are generated

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By what method does glucose enter into the cell?

facilitated diffusion through glucose transporters

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What happens in the first step of glycolysis?

Glucose is phosphroylated using ATP into Glucose 6-Phosphate (G6P)

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What enzyme catalyzes the first reaction in glycolysis?

Hexokinase

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What substrates are used by hexokinase, and what are its products (in step 1 of glycolysis)?

Substrates: Glucose, ATP, Mg²⁺

Products: Glucose 6-Phosphate, ADP, Mg²⁺

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What is the purpose of the first reaction in glycolysis?

To trap glucose in the cell (no transporter for phsophorylated glucose to “escape” through)

To destabilize glucose for further reatctions

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Is hexokinase reversible?

No, irreversible

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What is a kinase?

An enzyme that transfers a phosphoryl group from ATP to another molecule (or sometimes vice versa)

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What happens in step 2 of hydrolysis?

Glucose 6-phopate (G6P) is isomerized into fructose 6-phosphate (F6P)

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What enzyme catalyzes the second step of hydrolysis?

Phophohexose isomerase

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What is the mechanism for step 2 of glycolysis?

Multistep

Open the ring to linear form
Convert G6P → F6P
Close ring to cylic form

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What are the substrate and products of the phosphohexose reaction in step 2 of hydrolysis?

Substrates: Glucose 6-phosphate (G6P) , Mg²⁺ (not consumed)

Product: Fructose 6-Phosphate (F6P)

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Is phosphohexose isomerase reversible?

Yes (but recall it depends on ΔG, not ΔG⁰)

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What happens in the third step of glycolysis?

Phosphorylation of Fructose 6-Phosphate → Fructose 1,6-biphosphate (F-1, 6-BP)

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What enzyme catalyzes step 3 of hydrolysis?

Phosphofructokinase-1

(PFK-1)

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What are the substrates and products used by phsphofuctokinase-1 in step 3 of hydrolysis?

Reactant: Fructose 6-Phosphate, ATP, Mg²⁺ (not actually consumed)

Product: Fructose 1,6-biphosphate, ADP

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Is phosphofructokinase-1 reversible?

No, it is irreversible

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What is the rate-determening step of glycolysis?

Step 3; phosphorylation of Fructose 6-Phosphate. This is the “committed” step.

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What happens in step 4 of hydrolysis?

Cleavage of F-1,6-P → dihydroxyacectonephosphate (DHAP) and Glyceraldehyde 3-Phosphate (G3P)

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What enzyme catalyzes the step 4 of hydrolysis?

Aldolase

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What are the substrates and products of aldolase in the 4th step of hydrolysis?

Substrate: Fructose 1,6-biphosphate

Product: Dihydroxyacteonephosphate (DHAP) and Glyceraldehyde 3-Phosphate (G3P)

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Is aldolase reversible?

Study These Flashcards

Yes, reversible

What happens in step 5 of hydrolysis?

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Conversion of DHAP → G3P

What is the purpose of step 5 in hydrolysis?

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Convert DHAP into G3P because only G3P is used in phase 2 (“payoff phase”) of glycolysis

What enzyme catalyzes step 5 of hydrolysis?

Triose phosphate isomerase

What are the substrates and products used by triose phosphate isomerase in step 5 of glycolysis?

Substrate: DHAP Product: G3P

Is triose phosphate isomerase reversible?

Yes, reversible

What happens in step 6 of hydrolysis?

Oxidation and Phosphoylation of G3P to 1,3-biphosphoglycerate

What enzyme catalyzes step 6 of glycolysis?

glyceraldehyde 3-phosphate dehydrogenase

What are the required additional substrates for step 6 of hydrolysis?

NAD+ and Pi (inorganic phosphate)

Is glyceraldehyde 3-phosphate dehydrogenase reversible?

Yes

What is the purpose of step 6 of glycolysis?

To form 1,3-biphosphoglycerate (1,3-BPG) which has a high phsphoryl transfer potential (important for later)

What are the 2 "steps " of Step 6 of glycolysis and their thermondynamics?

1) Oxidation of G3P to a carboxylic acid using NAD+, forming NADH (energetically favourable) 2) Attachment of the carboxylic acid to a orthophosphate (or phosphate for short) (Not energetically favourable)

What connects the 2 "steps" of sixth step of hydrolysis together?

Thioester intermediate connects the steps such that the first step (oxidation of G3P) drives the 2nd reaction (Attachment of orthophosphate)

What is the mechanism of glyceraldehyde 3-phosphate dehydrogenase? (GAPDH)

1) Formation of a hemi(thio)acetal with cysteine resdiue in the active site 2) NAD+ oxidizes hemiacetal to form thioester, reducing NAD+ to NADH 3-4) NADH is replaced with a fresh NAD+ (3), which results in an inorganic phophate attacking the carbonyl and cleaving the reaction intermediate from cysteine (4), reforming the 1,3-BPG

How many molecules go through phase 2 of glycolysis?

2 molecules - generate 2 molecules of 1,3-BPG from 1 glucose, which eventually makes 2 molecules of pyruvate

What happens in step 7 of glucolysis?

1,3-BPG and ADP react to form 3-phosphoglycerate and ATP

What is substrate level phosphorylation and what is an example of it?

Refers to the formation of ATP from ADP and a phosphorylated intermediate, rather than from ADP and inorganic phosphate, Pi Example: Step 7 of glycolysis, Step 10 of glycolysis

What enzyme catalyzes step 7 of glucolysis?

Phosphoglycerate kinase

Is phosphoglycerate kinase reversible?

Yes

What are the substrates and products of step 7 of glycolysis?

Substrates: 1,3-BPG, ADP, Mg²⁺ (not consumed) Products: 3-phosphoglycerate, ATP

What happens in step 8 of glcolysis?

3-phosphoglycerate is converted to 2-phosphoglycerate

What enzyme catlyzes the 8th step of glycolysis?

Phospoglycerate mutase

Is phosphoglycerate mutase reversible?

Yes

What cofactor is required for step 8 of glycolysis?

2,3-biphosphoglycerate (2,3-BPG)

What is the mechanism of phosphoglycerate mutase?

1) Enz-His + 2,3-BPG ← phosphatase activity (removes Phosphate) → Enz-His-P + 2-phosphoglycerate 2) Enz-His-P + 3-phosphoglycerate ← Kinase activity (transfers phosphate) → Enz-His + 2,3-biphosphoglycerate