The Glycolysis Pathway:


Dehydrogenase (DH): "oxidation-reduction" reactions, look for NADH or FADH2

Kinase: "Substrate Level Phosphorylation"

Overall Pathway:

Glucose is metabolized to pyruvate.

All intermediates carry phosphate groups to lock them into the cell (stops diffusion).

Hexokinase / Glucokinase: both irreversible

Glucose + ATP ----> Glucose-6-phosphate + ADP


Catalyzes the phosphorylation of hexoses in general and is found in all cells that metabolize glucose.

Has a low Km (high affinity) so that it is active even at low glucose concentrations.


Glucose specific, found in liver.

Has a high Km (low affinity) to ensure a n appropriate response to elevation of glucose from the diet.

Phosphofructokinase-1 (PFK-1): irreversible

Fructose-6-phosphate + ATP ------> Fructose-1,6-bisphosphate + ADP

Rate-Limiting, Major Regulated Step.


Fructose-1,6-bisphosphate <----> Dihydroxyacetone phosphate +Glycerladehyde-3-phosphate

Completes the first phase of glycolysis.

These trioses are interconverted by triose phosphate isomerase ------------>

To produce a single product, glyceraldehyde-3-phosphate.

Two molecules of glyceraldehyde-3-phosphate continue through glycolysis.

Glyceraldehyde-3-phosphate Dehydrogenase: Oxidation-Reduction

Glyceraldehyde-3-phosphate + NAD+ + Pi <---> 1,3-Bisphosphoglycerate + NADH

NADH formed must be reoxidized to regenerate NAD+ to sustain glycolysis.

Energy released from this reaction is conserved as a high energy phosphate bond in 1,3-bisphosphoglycerate.

Inorganic phosphate, rather than ATP, provides the source of the phosphoryl group.

Aerobic Conditions:

Mitochondrial systems oxidize NADH and produce ATP.

Phosphoglycerate Kinase: "Substrate Level Phosphorylation"

1,3-bisphosphoglycerate + ADP <----> 3-phosphoglycerate + ATP

1,3-Bisphosphoglycerate is a high energy intermediate that drives the phosphorylation of ADP to ATP.

Remember: Two molecules are proceeding through glycolysis, so 2 ATP.

Pyruvate Kinase: "Substrate Level Phosphorylation"

Phosphoenolpyruvate + ADP -------> Pyruvate + ATP

Irreversible, Highly Regulated.

Produce 2 ATP.

Lactate Dehydrogenase: "Anaerobic"

Pyruvate + NADH ----> Lactate + NAD+

This step regenerates NAD+ for glyceraldehyde-3-phosphate dehydrogenase or glycolysis would STOP.

H4: heart isozyme, high affinity for lactate (low Km), allosterically inhibited by pyruvate.

When pyruvate is high oxidizes to Acetyl CoA.

M4: muscle isozyme, produces lactate in muscle when pyruvate is high.

Energy Yield:

Anaerobic (i.e. RBC): Pyruvate ---> Lactate, 2 ATP per glucose molecule.

Aerobic: Mitochondrial oxidation of NADH via electron transfer shuttles.

NADH ----> 2 ATP, a-glycerol phosphate shuttle (4 ATP per glucose)

NADH ----> 3 ATP, malate-aspartate shuttle (6 ATP per glucose)


Fructose Metabolism:

Occurs in liver.



Galactose Metabolism:

Occurs in liver.


UDP-Glucose is an activated form of glucose found as an intermediate in glycogen formation.

UDP-Glucose is recycled from UDP-Galactose thus, there is no NET change in concentration of this compound.

Fructose and Galactose Energy Production: still 2 ATP.

(Fructose enters at glyceraldehyde-3-phosphate)

(Galactose enters at glucose-6-phosphate)

© Dr. Noel Sturm 2020

Disclaimer: The views and opinions expressed on unofficial pages of California State University, Dominguez Hills faculty, staff or students are strictly those of the page authors. The content of these pages has not been reviewed or approved by California State University, Dominguez Hills.