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Difference between EMP, ED, and HMP pathway

Difference between EMP pathway, ED pathway and HMP pathway


EMP pathway (Embden-Meyerhof-Parnas pathway):
  • Also known as glycolysis, it is a metabolic pathway that converts glucose into pyruvate.
  • It involves a series of enzymatic reactions that ultimately generate ATP (energy) and pyruvate, which can further undergo fermentation or enter the citric acid cycle.
  • The EMP pathway occurs in the cytoplasm of cells and is central to both aerobic and anaerobic respiration.

ED pathway (Entner-Doudoroff pathway):
  • An alternative pathway to glycolysis for the oxidation of glucose to pyruvate.
  • It is utilized by some bacteria, archaea, and a few eukaryotes.
  • In the ED pathway, glucose is oxidized to pyruvate via a series of enzymatic reactions that generate ATP, NADH, and NADPH.
  • This pathway is particularly important in certain microorganisms living in environments with low oxygen levels.

HMP Pathway: 
  • HMP pathway (Hexose Monophosphate Pathway), also known as the Pentose Phosphate Pathway (PPP):
  • It is a metabolic pathway parallel to glycolysis that occurs in the cytoplasm of cells.
  • The primary function of the HMP pathway is to generate NADPH, which is essential for biosynthetic reactions and antioxidant defense mechanisms.
  • Additionally, the pathway produces ribose-5-phosphate, a precursor for the synthesis of nucleotides and other important cellular molecules.
  • The HMP pathway is especially active in tissues with high biosynthetic demands, such as the liver, adipose tissue, and rapidly dividing cells.

Difference between EMP pathway, ED pathway and HMP pathway:

Feature EMP Pathway ED Pathway HMP Pathway
ATP Generation per Glucose Molecule Generates 2 molecules of ATP Generates 1 molecule of ATP per glucose molecule Does not generate ATP
End Products Pyruvate or lactic acid Pyruvate or PGLAD Fructose 6 phosphate and PGLAD
Intermediates Consists of 3 and 6 carbon sugars Contains only 6 carbon sugars Consists of 3, 4, 5, and 6 carbon sugars
Anaerobic/Aerobic Nature Anaerobic breakdown of sugars Oxidative breakdown of sugars and sugar acids Not specified
Phases Preparative phase and payoff phase Not divided into any phases Oxidative irreversible and non-oxidative reversible phase
Reducing Power Molecules Does not generate any Generates NADPH+ and H+ Generates 2 molecules of NADPH+ and H+
Substrate Utilization Utilizes glucose as a substrate Can utilize glucose, gluconic acid, sugar acids Begins with glucose-6-phosphate
Pathway Universality Followed by plants, animals, and microbes Specialized pathway for certain bacteria Followed in specific eukaryotic tissues



Difference between EMP pathway, ED pathway and HMP pathway in Points:

Differences between the EMP (Embden-Meyerhof-Parnas) Pathway, the ED (Entner-Doudoroff) Pathway, and the HMP (Hexose Monophosphate) Pathway:

1. ATP Generation per Glucose Molecule:
  • EMP Pathway: Generates 2 molecules of ATP per glucose molecule.
  • ED Pathway: Generates 1 molecule of ATP per glucose molecule.
  • HMP Pathway: Does not generate ATP.

2. End Products:
  • EMP Pathway: Produces pyruvate or lactic acid.
  • ED Pathway: Produces pyruvate or phosphoglyceraldehyde (PGLAD).
  • HMP Pathway: Produces fructose 6-phosphate and PGLAD.

3. Intermediates:
  • EMP Pathway: Consists of 3 and 6 carbon sugars.
  • ED Pathway: Contains only 6-carbon sugars.
  • HMP Pathway: Consists of 3, 4, 5, and 6 carbon sugars.

4. Aerobic/Anaerobic Nature:
  • EMP Pathway: Follows anaerobic breakdown of sugars.
  • ED Pathway: Oxidative breakdown of sugars and sugar acids.
  • HMP Pathway: Not specified, but it is likely to be aerobic.

5. Phases:
  • EMP Pathway: Divided into preparatory phase and payoff phase.
  • ED Pathway: Not divided into any phases.
  • HMP Pathway: Divided into oxidative irreversible and non-oxidative reversible phase.

6. Reducing Power Molecules:
  • EMP Pathway: Does not generate any reducing power molecule.
  • ED Pathway: Generates NADPH+ and H+.
  • HMP Pathway: Generates 2 molecules of NADPH+ and H+.

7. Substrate Utilization:
  • EMP Pathway: Begins with the utilization of glucose as a substrate.
  • ED Pathway: Can utilize glucose, gluconic acid, mannonic acid (sugar acids).
  • HMP Pathway: Begins with the utilization of glucose-6-phosphate.

8. Pathway Universality:
  • EMP Pathway: Universal pathway followed by plants, animals, and microbes.
  • ED Pathway: Specialized pathway followed by certain bacteria like Pseudomonas, Xanthomonas, and Azotobacter.
  • HMP Pathway: Followed in eukaryotic adipose tissue, adrenal cortex, and mammary glands.
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