The Citric Acid Cycle (CC BY 3.0) by,
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
- Generation of energy in the form of ATP
- Generating NADH which is utilised in oxidative phosphorylation
- Citric Acid is regenerated
- 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.
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
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‘
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.
Sekhon MS, Ainslie PN, Griesdale DE. Clinical pathophysiology of hypoxic ischemic brain injury after cardiac arrest: a “two-hit” model. Crit Care. 2017 Apr 13;21(1):90. doi: 10.1186/s13054-017-1670-9.
Thorens B, Mueckler M. Glucose transporters in the 21st Century. American Journal of Physiology – Endocrinology and Metabolism. 2010;298(2):E141-E145. doi:10.1152/ajpendo.00712.2009.
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