ALDOHEXOSE: MOLECULAR STRUCTURE AND EXAMPLES - BIOLOGY - 2025

The aldohexoses are monosaccharides six carbon atoms containing an aldehyde group in their molecular structure. Its main function is to store chemical energy for use in metabolic activities. This energy is measured in kilocalories (Kcal) and one gram of aldohexose, like any other hexose, can generate up to 4 Kcal.

Aldehydes are all organic compounds that present in their molecular structure a functional group formed by a carbon atom, a hydrogen atom and an oxygen atom (-CHO).

Aldohexose and ketohexose. Taken and edited by Alejandro Porto.

Instead of having an aldehyde group, some hexoses can be attached to a ketone group, in that case they are called ketohexoses.

Molecular structure

The general formula for hexoses can be written as (CH ₂ O) ₆ or C ₆ H ₁₂ O ₆. These molecules are not arranged in a straight line, because angles are formed in the bonds between two carbon atoms.

Thanks to these angles that are formed, the carbon atoms at the ends are relatively close to each other. When a hexose molecule is in solution, a bond can then be established between two terminal carbon atoms. A molecule in the shape of a hexagonal ring is then formed.

The bond can also occur between a terminal carbon and a subminal carbon, forming in this case a pentagonal ring.

Examples of aldohexoses

Alosa

This aldohexose is considered a stereoisomer of glucose, from which it only differs in carbon 3 (epimer). Its chemical name is 6- (hydroxymethyl) oxano-2,3,4,5-tetrol. It is a colorless hexose, it is soluble in water, but it is almost insoluble in methanol. In nature it is very rare and has been isolated from a plant of African origin.

It has multiple applications in medicine. For example, it has anticancer properties, inhibiting the development of liver, prostate, ovarian, womb, and skin cancers, among others.

Other properties of D-allose include anti-hypertensive and anti-inflammatory activities. It favors the success of grafts, with less damage to the cells, it also reduces the production of segmented neutrophils.

Altrosa

Altrose is an aldohexose whose D- isomer is not found in nature, but has been produced artificially in the form of sweet syrup. It is soluble in water and practically insoluble in methanol.

On the other hand, the L-altrose isomer is rare in nature and has been isolated from bacterial strains. This sugar has a molecular weight of 180.156 g / mol, is stereoisomeric with glucose, and is an epimer at carbon 3 of mannose.

Altrosa. Taken and edited from Christopher King.

Glucose

Glucose is an aldohexose, isomer of galactose; It is one of the main products of photosynthesis and used as a primary source of energy in the cellular metabolism of most living beings. Produces 3.75 Kcal / gr.

Inadequate glucose metabolism can lead to hypoglycemia or diabetes. In the former, blood glucose concentrations are abnormally low, whereas in diabetes the reverse is true.

The D- (dextrose) isomer is the predominant form in nature. Glucose can be in linear or ring form of 5 or 6 carbons, with alpha or beta configuration.

In polymer form, animals and plants use it for structural purposes, or for energy storage. Among the main polymers of glucose are:

Cellulose

Main constituent of the cell wall of plants. It is a polymer formed by rings of glucose in its D-glucopyranose form.

Chitin

Polymer of cyclic nitrogenous derivatives of glucose, which is the fundamental constituent of the exoskeleton of arthropods.

Starch

Reserve substance of plants and many algae. It is a polymer of D-glucopyranose.

Glycogen

Another polymer of glucose rings, used as a reserve substance by animals and fungi.

Gulosa

Gulose is a hexose from the group of aldohexoses that does not exist freely in nature. It is an epimer in the C3 of galactose, that is, in its configuration it only differs from the latter in the third carbon of the chain.

The L- (L-gulose) isomer, for its part, is an intermediate product in the biological synthesis of L-ascorbate. This last compound, also known as Vitamin C, is an essential nutrient for humans, it cannot be biosynthesized by it, so it must be contained in your diet.

Gulose is a sugar soluble in water, but not very soluble in methanol, and cannot be used in the fermentative metabolism of yeasts.

Mannose

Mannose is a six-carbon aldose that only differs from glucose at C2. In cyclic form, it can form a five- or six-carbon ring in alpha or beta configuration.

In nature it is found as part of some plant polysaccharides, as well as some proteins of animal origin. It is a non-essential nutrient for humans, that is, it can be biosynthesized by this starting from glucose. It is very important in the metabolism of some proteins.

There are some congenital metabolic disorders due to mutations in enzymes related to the metabolism of this sugar.

Idosa

Idose is an aldohesoxa that does not exist in free form in nature, however, its uronic acid is part of some glycosaminoglycans that are important components of the extracellular matrix.

Among these glucasaminoglycans is dermatan sulfate, also known as chondroitin sulfate B; It is found primarily in the skin, blood vessels, heart valves, lungs, and tendons.

L-ylose only differs from D-galactose in the 5-carbon configuration.

Galactose

Galactose is an epimeric aldohexose of glucose at C4. It can exist in nature, both in linear form and as a 5 or 6 carbon ring, both in alpha and beta configuration.

In its 5-carbon ring form (galactofuranose) it is commonly found in bacteria, fungi, and also protozoa. Mammals synthesize galactose in the mammary glands to later form a galactose-glucose disaccharide, called lactose or milk sugar.

This aldohexose is rapidly converted to glucose in the liver in a metabolic pathway that is highly conservative in many species. However, mutations can occasionally occur in one of the enzymes related to galactose metabolism.

In these cases, the carrier of the mutant gene is unable to properly metabolize galactose, suffering from a disease called galactosemia. The consumption of galactose, even in small amounts, is harmful for those who suffer from this disease.

Galactose. Taken and edited from: Christopher King.

Talosa

It is a sugar that does not exist naturally, but scientists synthesize it artificially. It is an epimer at C2 of galactose, and of mannose at C4. It has high solubility in water and low in methanol.

D-talose is used as a substrate in tests to identify and characterize ribose-5-phosphate isomerase, present in bacteria of the genus Clostridium.

References

1. Hexose. On wikipedia. Recovered from en.wikipedia.org.
2. Hexos. Recovered from Biología-Geología.com.
3. Aldohexose. In Illustrated Glossary of Organic Chemestry. Recovered from che.ucla.udo.
4. TK Lindhorst (2007). Essentials of Carbohydrate Chemestry and Biochemestry. Wiley-VCH.
5. Mannose. On wikipedia. Recovered from en.wikipedia.org.
6. D - (+) - Talose. Recovered from sigmaaldrich.com.
7. Glucose. On wikipedia. Recovered from en.wikipedia.org.