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Aldose

Structure

Aldoses are a sub class of monosaccharides, which have a carbon backbone chain with many alcohol (hydroxy groups) and an aldehyde. (Ketones beget ketoses). They are polar molecules and very soluble in water thanks to their polyhydroxy nature. Monosaccharides are a type of carbohydrates, organic structures which can be thought of as having the ingredients for many water (H2O) molecules attached to the carbons in the chain, hence the the 'hydrate" of carbohydrate. For most organisms, carbohydrates are an important source of energy that is taken in as food, and broken down in a series of processes called metabolism. Aldoses feature prominently in two metabolic regimes, glycolysis which is the break down of sugars, and gluconeogenesis which is the opposite.

Nomenclature

Aldoses, like all carbohydrates are categorized first by the presence of an aldehyde or a ketone on the carbon chain. They can be further differentiated by the number of carbons in the main chain using greek prefixes. The minimum number of carbons in a backbone needed to form a molecule that is still considered a carbohydrate is 3, and carbohydrates with three carbons are called trioses. The only aldotriose is Glyceraldehyde, which has one chiral stereocenter and thus 2 possible enantiomers, D and L Glyceraldehyde. The most commonly discussed category of aldoses are those with 6 carbons, aldohexoses. . Some aldohexoses that are widely called by common names are

• D-(+)-Allose
• D-(+)-Altrose
• D-(+)-Glucose
• D-(+)-Mannose
• D-(-)-Gulose
• D-(+)-Idose
• D-(+)-Galactose

• D-(+)-Talose

to name a few

Aldoses can be further differentiated according to the number of carbon atoms they contain in the main chain using greek roots (tri-, tet-, pent-, hex-, etc), the common formula is to place the number signifier after aldo (or keto if it is a ketose), as in aldotriose.

Stereochemistry

Aldoses are commonly referred to by names specific to one stereoisomer of the compound. This distinction is especially vital in Biochemistry, as many systems can only use one enantiomer of the carbohydrate and not the other. However, aldoses are by no means locked into any one conformation forever, they can and do fluctuate between a couple of different forms.

Aldoses can tautomerize to ketoses in a dynamic process with an enol intermediate. This process is reversible and when discussing a mass group of sugars, aldoses and ketoses are thought of as being in equilibrium with each other due to the low energy barrier of the transition. However aldehydes and ketones are almost always more stable than their enol forms, so the aldo- and keto- forms are assumed to predominate at any given moment. This process, with it's enol intermediate, when applied occurring at other carbons on the chain allows stereoisomerization. Basic solutions exacerbate the interconversion of isomers.

Carbohydrates, especially those with more than 4 carbons, exist in an equibrium between two forms, often called the cyclic, and open-chain forms for clarity. Cyclic aldoses are usually drawn as Haworth projections, and open chain forms are commonly drawn as Fischer projections, both of which represent important stereochemical information about the forms the depict.

Stereochemical labels of carbohydrates are partially determined by two carbons, the aldehylic carbon (1), and the anomeric carbon (5) which distinguishes cyclic forms.

Metabolic Relevance

Glycolysis - glucose is a very very important part of this and you get to talk about fructose briefly, lol get into that glyceraldehyde and dihydroxyacetone. just all the aldoses relevant to this

Pentose Phosphate pathway

actually read that chapter because we did not actually cover that in class lulz

Polysaccharides- mention cellulose, a digluco glycan