Monosaccharides are the simplest carbohydrates. They are crystallizable, solid at room temperature, very soluble, white and sweet.
It is because of that sweet taste that they are called sugars. They are monomers, which means that they are a simple molecule that can not be divided into simpler compounds. This process of division is known as hydrolysis , And monosaccharides do not.
Chemical structure of glucose, a monosaccharide.
Monosaccharides have three to seven carbon atoms in their composition. The main monosaccharide that exists is glucose, which is the main food in the cells of living things.
Monosaccharides are composed of a linear carbon chain, meaning that it has no branching.
All the carbon atoms forming the chain, minus one, contain an alcohol group, which in its chemical formula is represented by the OH termination.
The carbon atom of the chain which does not have the alcohol group has a carbonyl group attached.
Carbonyl is a functional group having a double bond of carbon to an oxygen molecule. Depending on the location in the carbonyl chain of this carbonyl, the monosaccharides can be differentiated.
If the carbonyl is at one end of the carbon chain, an aldehyde group (-CHO) will form and the monosaccharides will then be aldoses.
If on the contrary the carbonyl is in any other position of the chain, it will be a ketone (-CO-) and the monosaccharides will be called ketoses
Featured examples of Monosaccharides
Glucose
It is the most important monosaccharide and is present in all living beings. This carbon chain is the necessary one so that the cells can exist since it gives them energy.
It is composed of a carbon chain of six carbon atoms, and complemented with twelve atoms of hydrogen and six of oxygen.
Group of Aldosas
This group is formed by the carbonyl at one end of the carbon chain:
Glyceraldehyde
This monosaccharide is the only one of the aldoses that is formed by three carbon atoms. So it is known as a triosa.
It is the first monosaccharide that is obtained in photosynthesis. In addition, it is part of metabolic pathways such as glycolysis.
Erythrosa and Treosa
These monosaccharides have four carbon atoms and one aldehyde group. The erythrosa and the treosa differ in the conformation of chiral carbons.
In the treosa they are in conformations D-L or L-D whereas in the erythrosa the conformations of both carbons are D-D or L-L
Patosas de Aldosas
Within this group we find carbonate chains that have five carbon atoms.
According to the position of the carbonyl we differentiate the monosaccharides Ribosa, Arabinosa, Xilosa and Lixosa
La Ribosa Is one of the major components of RNA and helps to form nucleotides like ATP that provide energy to the cells of living beings.
The Arabinosa Is one of the monosaccharides that appear in pectin and hemicellulose. This monosaccharide is used in bacterial cultures as a source of carbon.
The Xylosa Is also commonly known as wood sugar. Its main function is related to human nutrition, and is one of the eight essential sugars for the human body.
The Lixosa Is a rare monosaccharide in nature and is found in the bacterial walls of some species.
Hexose of Aldosas
In this group of monosaccharides are six carbon atoms. And they are also classified depending on the place where their carbonyl is found:
La Alosa Is a rare monosaccharide that has been obtained from the leaves of an African tree only
The Altrosa Is a monosaccharide found in some strains of bacteria Butyrivibrio fibrisolvens
La Manosa Has a composition similar to glucose and its main function is the production of energy for the cells
La Gulosa Is an artificial monosaccharide with a sweet taste that is not fermented by yeast
The elderly Is an epimer of glucose and is used as the energy source of the extracellular matrix of living cells.
Galactose Is a monosaccharide that is part of glycolipids and glycoproteins and is found primarily in brain neurons.
La Talosa Is another artificial monosaccharide that is soluble in water and with sweet taste
Group of Ketones
Depending on the number of carbon atoms we can distinguish the Dihydroxyacetone, formed by three carbon atoms and Erythrulose formed by four.
Also, if they have five carbon atoms and attending to the position of the carbonyl, we find Ribulose and Xylulose. And formed by six carbon atoms we have Sicosa, Fructose, Sorbose and Tagatose.
Disaccharides
In the Disaccharides Two molecules of monosaccharides are bound by the loss of a molecule of water, which is known as a glycosidic bond. Among them we distinguish:
Saccharose
This disaccharide is formed by the union of glucose and fructose monosaccharides. It is also called common sugar.
Lactose
This disaccharide is formed by a molecule of glucose and one of galactose. It is found in dairy products.
Maltose, Isomaltosa, Trehalose and Celobiosa
These disaccharides are made up of two glucose molecules, depending on where they occur in binding they are called in a different way.
Polysaccharides
Polysaccharides are formed by the bonding of many monosaccharide molecules. Here we explain the most important and most common of nature:
Starch
Composed of amylose polysaccharides and amylopectin, it is the reserve carbohydrate of vegetables. And it is important for human nutrition
Glycogen
This is composed of branched chains of glucose. It is the energy reserve of animals and is found in the muscles and in some cells of the brain.
Cellulose
It is composed of glucose molecules and is the most abundant biomolecule and forms part of terrestrial biomass
Chitin
It is composed of acetylglucosamine units and forms part of the cell walls of fungi.
References
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- AKSELROD, SOLANGE, et al. Glucose /? J. Physiol , 1975, vol. 228, p. 775.
- DARNELL, James E., et al. Molecular cell biology . New York: Scientific American Books, 1990.
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- ZAHA, Arnaldo; FERREIRA, Henrique Bunselmeyer; PASSAGLIA, Luciane MP. Basic Molecular Biology-5 . Artmed Editora, 2014.
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