What are monosaccharides?


The monosaccharide also known as simple sugar , are any of the basic compounds serving as basic components of carbohydrates . Monosaccharides are polyhydric aldehydes or ketones ; that is, they are molecules with more than one hydroxyl group (-OH) and one carbonyl group (C = O) at the terminal carbon atom (aldose) or at the second carbon atom (ketosis). The carbonyl group combines in aqueous solution with a hydroxyl group to form a cyclic compound ( hemi-acetal or hemi-ketal). The resulting monosaccharide is a water soluble crystalline solid .


What are monosaccharides

Monosaccharides are the simplest carbohydrates that we can find and are chemically made up of a single chain of polyalcohols with an aldehyde or a ketone group, so they cannot be decomposed by hydrolysis .

  • Characteristics of monosaccharides
  • Classification
  • Structure
  • Formula
  • Physical properties of monosaccharides
  • Chemical properties
  • Applications
  • Monosaccharide foods
  • Examples

Characteristics of monosaccharides

The main characteristics of monosaccharides are:

  • Monosaccharides are a source of energy ; most of them provide about 4 calories (kilocalories) per gram, just like other carbohydrates.
  • They are non-essential nutrients , so the body can make all it needs for proper function from other nutrients.
  • They do not need to be extracted from other foods.
  • They are absorbed in the small intestine and can be absorbed without being previously broken down by enzymes in the intestines.
  • They are the simplest carbohydrates and cannot be hydrolyzed .
  • They are made up of C, H and O in a ratio of 1: 2: 1 respectively.
  • They are of solid consistency , are crystalline , white in color and have a very sweet flavor.
  • Depending on the number of carbons that make it up, the osa ending is used .
  • The best known are glucose , fructose, and galactose .


Monosaccharides can be classified depending on the number of carbon atoms they have and according to the position that the carbonyl group occupies in the molecule . Depending on the number of carbon atoms, they are divided into:

  • Trioses : 3 carbon atoms
  • Tetrosses : 4 carbon atoms
  • Pentose : 5 carbon atoms
  • Hexos : 6 carbon atoms
  • Heptoses : 7 carbon atoms

Whenever the carbonyl group is located at the end of the molecule, the monosaccharide will be an aldose . When the carbonyl group is not at the end, but in an intermediate position, the monosaccharide will then be a ketosis .


They are made up of carbon chains of 3 to 12 carbon atoms . These chains are named by adding the suffix – ose to the prefix that indicates the number of carbons in the molecule. The most abundant and of greatest biological importance are the trioses , pentoses and hexoses .

Those monosaccharides that have an aldehyde functional group (-CHO), always located in C1, are called aldoses, and those that have a ketone group (-CO-), always located in C2, are called ketoses.

Most have asymmetric carbons, which means that they have carbons attached to four different groups.


Monosaccharides have three to seven carbon atoms1 and their empirical formula is known as (CH2O) n, where n ≥ 3.

Physical properties of monosaccharides

Monosaccharides have a solid consistency and are crystalline or white in color . They have a sweet taste and are soluble in water. They have among their properties the ability to have spatial or optical isometry . The number of isomers that a monosaccharide has will depend on the number of asymmetric carbon atoms that its molecule has.

They have optical isomerism so they are optically active since they can rotate the plane of polarized light.

Chemical properties

Monosaccharides have different chemical properties, for example, they are molecules that have a high degree of radioactivity . All of them are soluble in water, and very little in ethanol, in addition to being insoluble in ether . They have a reducing power due to their carbonyl group reducing characteristics and their reaction to reagents such as Tollens, Benedict or Fehling, form the first property gluconic acid product used in reducing sugars in urine .

They can also produce glycosides when a monosaccharide reacts to alcohol. This chemical reaction can also happen between two monosaccharides, giving rise to a disaccharide.

They have the ability to mutarrotation because they have free rotation of hydroxyl and hydrogen from the carbonyl group


Some of the uses that can be given to monosaccharides are:

  • They are used as a source of energy because acceptable amounts of ATP are formed in their oxidation.
  • They can be transformed into lipids when there are excess carbohydrates in the diet, and they are stored in adipose tissue or in amino acids.
  • They are part of more complex structures such as glycoproteins , glycolipids, and nucleotides .
  • They are precursors of oligo and polysaccharides .
  • They comply with the principle of use because they are capable of performing different functions within the body.
  • They represent the main source of energy for all living beings because they oxidize easily. In this way, they are a source of fuel for our metabolism .

Monosaccharide foods

Some foods that have monosaccharides are:

  • Glucose : honey, fruits, dairy products, nuts, cereals, vegetables and breads.
  • Lactose : butter, margarine, yogurt, ice cream, milk, custard, cheese.
  • Fructose : it is found in fruits, honey and in vegetables, vegetables, vegetable oils and cereals.


Among the examples of monosaccharides that we can cite are:

  • Glyceraldehyde
  • Eritrosa
  • Treosa
  • Pentosas by aldosas
  • Ribose, arabinonose, and xylose
  • Disaccharides such as sucrose, lactose, and maltose.
  • Polysaccharides such as starch, glycogen, and cellulose.

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