Mitochondria

Each mitochondrion is surrounded by a double membrane, and the inner membrane folds into projections called cristae [4]. Mitochondria carry their own ribosomes and transfer RNAs, but they depend on genes in the cell nucleus for many of the messenger RNAs they need [4]. They are believed to have arisen from aerobic bacteria that formed a symbiotic relationship with early cells [4].

Making ATP is only part of the job. A review in Cell describes mitochondria as producing ATP and many biosynthetic intermediates, molecules that cells use to build other substances [2]. The same review says mitochondria also contribute to cellular stress responses such as autophagy and apoptosis [2]. Autophagy is the breakdown and digestion of parts of a cell's own contents [7], and apoptosis is a regulated, genetically programmed form of cell death [8]. The review also describes them as a dynamic, interconnected network that is integrated with other parts of the cell and that influences communication between cells and tissues [2].

On NootropicsWork, mitochondria appear in "how it works" sections, which describe mechanism, and never as a graded outcome. Creatine is a common example. A trial report describes creatine as a buffer for the cytosolic and mitochondrial pools of ATP in the brain [1], and a pharmacokinetic review says the clinical relevance of creatine supplements rests mainly on its role in ATP generation [3].

A plausible mechanism is a reason to run a trial, not a result. Whether a supplement changes how people think, sleep or perform is a separate question that needs placebo-controlled studies measuring those outcomes, and our compound pages grade that evidence on its own terms.

• Nucleotide: ATP is an adenine nucleotide carrying three phosphate groups [5].
• Elemental magnesium: magnesium is important for many enzymes, especially those involved in oxidative phosphorylation [6].
• Creatine: the compound page grades the trial evidence.