Glycolysis Steps

Preparatory phase

first five steps

Preparatory phase’s energy

uses 2 ATP

Payoff Phase

second five steps

Payoff Phase Energy Usage

4 ATP, 2 NADH made

Glycolysis Overall Energy

uses 2 ATP

makes 2 NADH, 4 ATP

total: 2 NADH, 2 ATP made

Hexokinase is what enzyme class 

transferase

Hexokinase refers to what step

Step 1

Reagents for Hexokinase

Glucose

Products for Hexokinase Step 

Glucose-6-Phopshate (G6P)

Hexokinase Step’s energy 

endergonic due to the use of ATP (-4.0 kcal/mol)

Hexokinase Reaction Formulas

Glc + Pi → Glc-6-P

ATP →ADP + Pi

Once glucose has been phosphorylated

it cannot leave the cell (can’t traverse the membrane)

after step 1!

Phosphohexose Isomerase is what enzyme class

isomerase

Phosphohexose Isomerase refers to what step

2

Phosphohexose Isomerase’s reagents

Glucose-6-Phosphate

Phosphohexose Isomerase’s product 

Fructose-6-Phosphate

Phosphohexose Isomerase’s Energy

Endergonic due to the 6 membered ring becoming a 5 membered ring (+0.4)

∆G⁰’ Formula

∆G⁰’ = -RTlnKeq

Phosphofructose Kinase-1 (PRK-1)’s Enzyme Class

transferase

Phosphofructose Kinase -1 (PFK-1) refers to what step

3

Phosphofructose Kinase -1’s reagaent

Fructose-6-Phosphate 

Phosphofructose Kinase -1’s product

Fructose- 1,6- Biphosphate (FBP)

Phosphofructose Kinase -1’s Energy 

Exergonic due to use of ATP -3.4 kcal/mol

use ATP to make ADP

Phosphofructose Kinase -1’s Formulas

F6P + Pi → FBP

ATP → ADP + Pi

Aldolase is what enzyme class

synthase/lyase

Aldolase refers to what step

4

Aldolase’s reagent

Fructose-1,6-Biphosphate (FBP)

Aldolase’s products

Glyceraldehyde-3-phosphate (GAP) and Dihdroxyacetone Phosphate (DHAP )

Aldolase’s Energy

Endergonic due to sigma bonds becoming pi bonds

+5.7 kcal/mol

Step 4’s products ___ in the pathway

move forward

This is important because they will move forward in the next steps in glycolysis and FBP will continue to react to take these products place. 

Triose Phosphate Isomerase (TIM) is what enzyme class 

isomerase

Triose Phosphate Isomerase refers to what step

5

Triose Phosphate Isomerase ’s reagent

Dihydroxyacetone Phosphate (DHAP)

Triose Phosphate Isomerase’s product

Glyceraldehyde-3-Phosphate (GAP)

Triose Phosphate Isomerase’s Energy

endergonic due to a ketone becoming an aldehyde (+7.5 kcal/mol)

Step 5’s Products _____ in the Glycolysis pathway

move forward

This is important because they will move forward in the next steps in glycolysis and FBP will continue to react to take these products place. 

GAP Dehydrogenase is what enzyme class

oxidoreductase

GAP Dehydrogenase is used in what step

6

GAP Dehydrogenase’s reagent

Glyceraldehyde-3-phosphate

GAP Dehydrogenase’s product

1,3- Biphosphoglycerate (BPG) & NADH (2)

GAP Dehydrogenase’s energy

+1.5 kcal/mol

Mercury inhibition

Inhibits Step 6. 

Shuts down the reaction by interacting with the Sulfur molecule

Arsenate Inhibition

can replace the Pi as a substrate for GAP DH. The resulting product of arseno analog is unstable and falls off. Step 7 is skipped, which is very bad because Step 7 makes ATP. 

GAP Dehydrogenase's Formulas

GAP + Pi → BPG +2e-

NAD⁺ + 2e- → NADH

GAP Dehydrogenase’s Oxidation and Reduction

GAP is oxidized to BPG.  NAD⁺ is reduced to NADH. 

Phosphoglycerate Kinase is what enzyme class

Transferase

Phosphoglycerate Kinase refers to what step

step 7

Phosphoglycerate Kinase’s reagents

1,3- Biphophoglycerate (BPG)

Phosphoglycerate Kinase’s products

3-Phosphoglycerate & 2 ATP!!

Phosphoglycerate Kinase involves

Substrate Level Phosphorylation

Phosphoglycerate Kinase’s Energy

Exergonic due to the phosphoryl ester becoming a carboxylate

-4.5 kcal/mol

Phosphoglycerate Kinase’s Formula

BPG → 3 PG + Pi

ADP + Pi → ATP

In red blood cells, ~20% of glycolysis is used to make

2,3 BPG

This is an example of how cells like to use what they already have

Phosphoglycerate Mutase is what enzyme class

isomerase

Phosphoglycerate Mutase refers to what step

step 8

Phosphoglycerate Mutase’s Reagent

3- Phosphoglycerate

Phosphoglycerate Mutase’s product

2-Phosphoglycerate (2PG)

Phosphoglycerate Mutase’s Energy

Endergonic due to closer negative charges 

+1.0 kcal/mol

Enolase is what enzyme class

synthase/lyase

Enolase refers to what step

step 9

Enolase’s reagent

2 Phosphoglycerate (2PG)

Enolase’s product

Phosphoenolpyruvate (PEP)

Enolase (step 9)’s energy

Endergonic due to pi bond alkene formation

+0.4 kcal/mol

Pyruvate Kinase is what enzyme class

Transferase

Pyruvate Kinase refers to what step 

step 10

Pyruvate Kinase (step 10) reagent

Phosphoenolpyruvate (PEP)

Pyruvate Kinase (step 10) products

Pyruvate and 2 ATP!S

Pyruvate Kinase (step 10) Energy

Exergonic due to enol becoming a keto and removal of the negative repulsion (closeness of the negative charges) 

-7.5 kcal/mol

Pyruvate Kinase (step 10) involves

Substrate Level Phosphorylation

Pyruvate Kinase (step 10) Formulas

PEP → Pyruvate + Pi

ADP + Pi → ATP

Which steps involve substrate level phosphorylation (make ATP)

Step 7 (Phosphoglycerate Kinase) and Step 10 (Pyruvate Kinase)

Which steps involve oxidation/reduction (make NADH)?

Step 6 (GAP DH)

What is the net energy carriers made from 1 Glucose to 1 Pyruvate?

2 ATP and 2 NADH

Which steps are exergonic steps?

1,3,7,10

Which steps are endergonic?

2,4,5,6,8,9

Which steps are regulated?

1,3,10

What inhibits Hexokinase?

Its product (G6P) inhibits it. 

This controls the amount of G6P in the cell

classical feedback inhibition

Which step is committed?

Step 3

Why is step 3 the committed step?

It’s the earliest irreversible step exclusive to glycolysis. Step 1 is too early because other sugars feed into glycolysis after this step. Step 10 is too late in the pathway. 

PRK-1 is inhibited by 

ATP 

stabilizes the T-state (right shift)

PRK- 1 is activated by 

Fructose-2,6-Biphosphate (F2,6BP)

stabilizes the R state (left shift) 

indirect feedback activation

Pyruvate Kinase is inhibited by

ATP

Pyruvate Kinase is activated by

Fructose 1, 6, Biphosphate (Step 3 product) 

classic feedback activation