D-glucose
Glucose is a primary source of energy for the brain, and hence its availability influences psychological processes.
When glucose is low, psychological processes requiring mental effort
(e.g., self-control, effortful decision-making) are impaired.[5][6][7][8]
Glucose (/ˈɡluːkoʊs/ or /-koʊz/; C6H12O6, also known as D-glucose, dextrose, or grape sugar) is a simple sugar (monosaccharide) and an important carbohydrate in biology.
Cells use it as the primary source of energy[1] and a metabolic intermediate. Glucose is one of the main products of photosynthesis and fuels for cellular respiration. Glucose exists in several different molecular structures, but all of these structures can be divided into two families of mirror-images (stereoisomers).
Only one set of these isomers exists in nature, those derived from the "right-handed form" of glucose, denoted D-glucose. D-glucose is sometimes referred to as dextrose, although the use of this name is strongly discouraged. The term dextrose is derived from dextrorotatory glucose.[2]
This name is therefore confusing when applied to the enantiomer, which rotates light the opposite direction. Starch and cellulose are polymers derived from the dehydration of D-glucose.
The other stereoisomer, called L-glucose, is hardly ever found in nature.
The name "glucose" comes from the Greek word glukus (γλυκύς), meaning "sweet", and is the preferred name. The suffix "-ose" denotes a sugar.
The reason that glucose, and not another monosaccharide such as fructose, is so widely used in organisms is not clearly understood.
One reason might be that glucose has a lower tendency, relative to other hexose sugars, to react non-specifically with the amino groups of proteins.
This reaction (glycation) reduces or destroys the function of many enzymes.
The low rate of glycation is due to glucose's preference for the less reactive cyclic isomer.
Nevertheless, many of the long-term complications of diabetes (e.g., blindness, renal failure, and peripheral neuropathy) are probably due to the glycation of proteins or lipids.[3]
In contrast, enzyme-regulated addition of glucose to proteins by glycosylation is often essential to their function.[citation ^needed]