Glycolysis

Steps of Glycolysis (enzymes, reactions)

Hexokinase

Step 1

Conversion of glucose to glucose-6-phosphate

glucose is phosphorylated using 1 ATP molecule

ATP → ADP (tri- to di-)

Phosphogluco-isomerase

Step 2

Rearrangement of glucose 6-phosphate (G6P) into fructose 6-phosphate (F6P) (fructose is an isomer of glucose)

6-member ring to 5-member ring

Phosphofructokinase

Step 3

Fructose-6-phosphate is converted to fructose- 1,6-bisphosphate (FBP)

uses 1 additional ATP molecule for second phosphate

ATP → ADP

Aldolase

Step 4

cleavage of FBP to yield two 3-carbon molecules

Yields glyceraldehyde-3-phosphate (GAP) dihydroxyacetone phosphate (DHAP) (isomers)

Triosephosphate isomerase

Step 5

Converts DHAP molecules into GAP to continue onto the next step

Should have two GAP molecules at the end

Glyceraldehyde-3-phosphate

dehydrogenase

Step 6

1. Glyceraldehyde-3-phosphate (GAP) is oxidized by the coenzyme nicotinamide adenine dinucleotide (NAD)

2. The molecule is phosphorylated by the addition of a free phosphate group yielding 1,3-bisphosphoglycerate and NADH

Phosphoglycerokinase

Step 7

1,3 bisphoglycerate is converted to 3-phosphoglycerate

Phosphate is transferred to a molecule of ADP yielding ATP

happens x2 with both 1,3 bisphoglycerate molecules, yielding a total of 2 ATP

Phosphoglyceromutase

Step 8

Rearrangement of the position of the phosphate group on the 3-phosphoglycerate molecule, making it 2-phosphoglycerate

Enolase

Step 9

Conversion of 2-phosphoglycerate to phosphoenolpyruvate (PEP)

Dehydration yielding H₂O

Pyruvate kinase

transfers a P from phosphoenolpyruvate (PEP) to ADP to form pyruvic acid and ATP

happens x2 with both phosphoenolpyruvate molecules, yielding 2 ATP and 2 pyruvate molecules

Glycolysis Equation

Energy Generating Steps

Steps 7 & 10 = +4 ATP

Energy Consuming Steps

Steps 1 & 3 = -2 ATP

Reaction Coupling

Endergonic (unfavorable) reactions are paired with exergonic (favorable) reactions to proceed

Steps 1 & 3 utilize this by coupling phosphorylation with ATP hydrolysis

Aerobic Conditions

Pyruvate is converted into Acetyl CoA, enters the TCA cycle

NADH transfers its electrons into the ETC

Anaerobic Conditions

Fermentation

Pyruvate is reduced into either lactate (animals/bacteria) or ethanol and CO₂ (fungi/plants)

NADH transfers electrons to pyruvate, oxidizes back to NAD to restart glycolysis

Redox Reactions

An oxidation-reduction (redox) reaction is a type of chemical reaction that involves a transfer of electrons between two molecules

Glycolysis: Step 6 GAP is oxidized by NAD, NAD is reduced to NADH