The Brain Hypometabolism Hypothesis Part 75: Adenosine Diphosphate


Ball and Stick Model of ADP by Jynto (Public Domain)

Adenosine Diphosphate (ADP) is a precursor of ATP. ATP is synthesised from ADP and inorganic Phosphate by the enzyme ATP Synthase. ADP contains Adenine and Ribose both of which are also found in RNA.

What is ATP Synthase?


ATP Synthase by ALoopingIcon using QuteMol (CC BY 2.5)

ATP Synthase is an enzyme that combines inorganic phosphate and Adenosine Diphosphate to form Adenosine Triphosphate (ATP). This in turn is used as a source of energy.

What is Oxidative Phosphorylation?

Oxidative phosphorylation is a series of chemical reactions in which electrons are transferred, nutrients are metabolised and ATP is formed.

Brain Hypometabolism Hypothesis

The Brain Hypometabolism Hypothesis focuses on energy metabolism. More specifically the hypothesis states that

Energy hypometabolism in the brain leads to neuropathology


Human Metabolism by Frozen Man (CC BY 4.0)

What is Metabolism?

Metabolism can be defined as the chemical processes that occur in living organisms. There are three types of metabolic processes

(a) Generation of energy

(b) Generation of basic chemicals including fatty acids, amino acids and sugars

(c) Elimination of Nitrogen waste products



Glycolysis is one of the key pathways for energy metabolism in the human body. In this metabolic pathway the molecule Glucose is converted into Pyruvate. This pathway generates energy in the form of ATP. This pathway however does not use oxygen although the products generated are metabolised using oxygen. This is relevant to the bigger picture of energy metabolism in the brain.


Acetyl CoA Space Filling Molecule by Benjah-bmm27 (Public Domain)

What is Acetyl Coenzyme A?

Acetyl Coenzyme A is an important molecule for many pathways involved in energy metabolism. Acetyl Coenzyme A is derived from

(a) Glucose via the Glycolysis pathway

(b) Amino acids via Acetoacetyl-CoA, Pyruvate and directly through multiple pathways

(c) Fatty acids via Beta-oxidation

Vitamin B5 is required for the synthesis of Acetyl CoA.

The Citric Acid Cycle

The Citric Acid Cycle (CC BY 3.0) by Narayanese, WikiUserPedia, YassineMrabet, TotoBaggins, Wadester16

The Citric Acid Cycle is one of the main energy metabolism pathways in humans. Acetyl Co-A which is generated from other pathways is utilised in the Citric Acid Cycle. The Citric Acid Cycle has a number of properties

  1. Generation of energy in the form of ATP
  2. Generating NADH which is utilised in oxidative phosphorylation
  3. Citric Acid is regenerated
  4. Carbon Dioxide is produced

The Citric Acid Cycle takes place in the Mitochondria.

The Citric Acid Cycle is important for the discussion of the Brain Hypometabolism Hypothesis where we have already discussed the metabolism of Glucose.

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