Biochemistry

Monosaccharides -definition, structure, types, examples

Table of Contents show 1 What are Monosaccharides? 2 Vant Hoff’s Rule of ‘n’ 3 Classifications of Monosaccharides 4 Characteristics of Monosaccharide...

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This article writter by MN Editors on May 04, 2022

Microbiology Notes is an educational niche blog related to microbiology (bacteriology, virology, parasitology, mycology, immunology, molecular biology, biochemistry, etc.) and different branches of biology.

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Monosaccharides -definition, structure, types, examples
Monosaccharides -definition, structure, types, examples

What are Monosaccharides?

Monosaccharides are the most basic carbohydrates because they can’t be hydrolyzed to smaller carbs. They are the basic unit of Carbohydrates. They consist of just 1 carbohydrate moiety. The general chemical formula for unmodified monosaccharides is (C*H2O)”n”, literally meaning “carbon Hydrate”. This is referred to as the formula for empirical purposes.

In this formula, the “n” ranges between 3-6, and often seven. This means that the natural. of carbon atoms in monosaccharide ranges from minimum 3 to 7.

The monosaccharides with the smallest size (for which there is a n of 3,) include dihydroxyacetone as well as the glyceraldehyde. However, not all carbs are able to meet this exact description of the stoichiometric (e.g. Uronic acids, sugars that are deoxy-sugars, such as fucose) however, neither are all chemical compounds that meet this criteria immediately classified as carbohydrates.

Vant Hoff’s Rule of ‘n’

The number of imaginable isomers of any delivered compound relies upon the digit of the molecule’s asymmetric carbon atoms.

Based on this principle 2n is the number of possible isomers for that compound in which ‘n’ represents the number of carbon asymmetric Atoms within the compound.

Classifications of Monosaccharides

Classifications of Monosaccharides based on number of Carbon atom

Monosaccharides can be classified based on the amount of carbon atoms that they possess. The following groups can be classified as follows:

  • Triose: Triose can be described as a monosaccharide with three carbons. An example is glyceraldehyde-3-phosphate (C3H7O6P). It is a trise which functions as an intermediary in various metabolic pathways of carbohydrate.
  • Tetrose: A tetrose an monosaccharide that has 4 carbon atoms. The most common tetroses that occur naturally are D-erythroseand D-threose and D-erythrulose. The Erythrose, C4H8O4, is a Tetrose that has one aldehyde group. It was first discovered in 1849 by French pharmacist Louis Feux Joseph Garot in 1849. Erythrose is one of the metabolite found in the Calvin cycle and also in the pentose-phosphate pathway. Threose is also a tetrose. It is an enantiomer of the erythrose. Another alternative is the erythrulose. It is the exact chemical formula: C 4H 😯 4 . However, erythrulose is an ketotetrose that has an ketone group within its structure.
  • Pentose: A pentose can be described as monosaccharide with five carbons. Examples of pentoses include arabinose, deoxyribose, lyxose, xylose as well as xylulose. Ribose (chemical formula C5H10O5) and deoxyribose (chemical formula C5H10O4) are the constituents of nucleotides and nucleic acid. Particularly, ribose is the pentose sugar constituent of the nucleotides of DNA, while deoxyribose forms the sugar component of DNA nucleotides.
  • Hexose: Hexose is monosaccharide that has six carbons. The most common hexoses are galactose, mannose and glucose Idose, gulose, altrose, talose, allose piscose, fructose sorbose and tagatose. Particularly, glucose is the most well-known Hexose used as an intermediate in the metabolic process of cell respiration. Extra glucose is stored as glycogen in animals , and by plants as starch.
  • Heptose: Heptose is a monosaccharide with seven carbons. Examples of naturally-occurring heptoses are L-glycero-D-manno-heptose and sedoheptulose. The chemical formula for them is C7H14O7. They are the first intermediates in biosynthesis of lipids A.
  • Octose: Octose is a eight-carbon monosaccharide. Octoses possess an chemical formula of C8H16O8. An example is methylthiolincosamide, i.e. the sugar moiety of antimicrobial agent lincomycin.
  • Nonose: Nonoses are monosaccharide with nine carbons. Examples of nonoses include sialic acid, neuraminic Acid legionaminic acid Psudaminic Acid. Neuraminic acid (chemical formula of C9H17NO8) specifically is an artificial nonose.
Classifications of Monosaccharides based on number of Carbon atom
Classifications of Monosaccharides based on number of Carbon atom

It is important to note that these are terms (e.g. triose, tetrose, pentose, etc.) are distinct from trisaccharide (tetrasaccharide), pentasacc and so on because these terms refer to the quantity of monosaccharide units within the polymer, i.e. the three monosaccharides are different from four five monosaccharides and so on.

Classifications of Monosaccharides based on the type of carbonyl group

Monosaccharides can also be classified according to the carbonyl group that they are part of:

  • Aldose, (-CHO) (aldehyde) A monosaccharide which includes an aldehyde groups(-CHO)
  • Ketose, C=O (ketone) A ketose is one that has one of the ketose (C=O).
Classifications of Monosaccharides based on the type of carbonyl group
Classifications of Monosaccharides based on the type of carbonyl group

Characteristics of Monosaccharide

  • The most basic type are the sugars that have simple structures known as monosaccharides. They are unable to be further broken down into simpler sugars through hydrolysis. Monosaccharides, however, can be combined with each other to create more complex varieties.
  • Glycosidic bonds (also known as glycosidic linkages) are covalent bonds that connect monosaccharides. The union of simple sugars referred to as disaccharide, whereas carbohydrates that consist of 3 to 10 simple sugars are referred to as the oligosaccharides. The ones with more monosaccharide units are referred to as polysaccharides.
  • The process of joining monosaccharide unit is referred to as dehydration synthesizing because it causes that water is released as an resultant. This process, however, is reverse-able. Complex carbohydrates can be broken down into simple sugars for instance, glycogenolysis. glycogen that is stored is transformed into glucose units which can be used for the process of energy metabolism.
  • A monosaccharide is characterized by an overall chemical formula of CnH2nOn, and its physical structure can be described as H(CHOH)nC=O(CHOH)mH. Its ratio of hydrogen oxygen atoms to hydrogen atoms is usually 2:1. One exception is deoxyribose, which is a form of monosaccharide that is found in DNA. Due to this formula rule for chemical formulas monosaccharides as well as other carbohydrates are described as carbon hydrates.
  • Monosaccharides can be transparent, crystalline solids and have a sweet taste. They are dissolved in water, and can be found in the form of syrups or liquid sugar. Similar to other carbohydrate, monosaccharides are organic compounds. They have carbon that is covalently bound to other elements including carbon-carbon (C-C) as well as Carbon-Hydrogen (C-H).

Reactions Of Monosaccharides

1. Tautomerization or enolization

The process of moving hydrogen atoms to one carbon atom another in order to create enediols is called automerization. Sugars that have an omeric carbon atom are subject to tautomerization within alkaline solutions. When glucose is placed in alkaline solution for some time the sugar undergoes isomerization to produce D-fructose as well as D-mannose. This reaction– known as the Lobry de Bruyn-von Ekenstein transformation–results in the formation of a common intermediate–namely enediol–for all the three sugars. The enediols are extremely reactive so sugars in an alkaline solutions can be powerful reducers.

Tautomerization or enolization
Tautomerization or enolization

2. Reducing properties

They are classified by their ability to be either reducing or non-reducing. The property of reducing is attributed by the aldehyde free, or keto group of carbon anomeric. In the lab, a variety of tests are conducted to discover the action of sugars on reducing. They include Benedict’s test the Fehling’s test and Barfoed’s tests etc. The reduction is far more effective in the alkaline medium than the acid medium. The enediol form (explained earlier) or sugars convert cupric Ions (Cu2+) of copper sulphate cupsrous Ions (Cu+) and result in a yellow precipitate of cuprous hydroxide, or an orange crystal of copper oxide, as illustrated in the next. It should be noted that the reduction property of sugars does not allow for the identification of particular sugar since it is an all-encompassing reaction.

Monosaccharides

3. Oxidation

In the event of an agent used for oxidation and the type of oxidizing agent used, the terminal aldehyde (or keto) or the terminal alcohol, or both of them can be converted to oxidation. For instance, consider glucose : 1. Oxidation of the group aldehyde (CHO = COOH) leads to the formation of gluconic acid.

2. Oxidation of the terminal alcohol groups (CH2OH = COOH) results in creation of glucuronic acids.

4. Reduction

If used in conjunction with reducing agents such for sodium amalgam, the aldehyde or keto monosaccharide groups are reduced to alcohol of the same type as shown by the general formula

Reduction

The principal monosaccharides and their alcohols are described below.

Reduction
Reduction

Sorbitol and dulcitol , when accumulated in tissues in huge amounts create strong osmotic reactions leading to cell swelling, and also certain pathological conditions. e.g. cataract, peripheral neuropathy, nephropathy. Mannitol can be used to decrease the intracranial pressure through forced diuresis.

5. Dehydration

In the event of treatment with sulfuric acid concentrated, the bmonosaccharides are dehydrated with an

removal of three water molecules. Therefore, hexoses produce furfural hydroxymethyl while pentoses provide furfural upon dehydration. These furfurals may condense to phenolic substances (D-naphthol) to create colour-changing products. This is the chemical foundation of the well-known Molisch test. In the case of oligo- and polysaccharides they are first hydrolyzed to monosaccharides using acid. This is later followed by dehydration.

Monosaccharides
Monosaccharides
  • Bial’s test: Pentoses react with powerful HCl to create furfural derivatives that then react with orcinol and form a green colored complexes. Bial’s test can be useful to detect xylose in urine when there is a need for pentosuria.
Bial's test
Bial’s test | Image Source: https://upload.wikimedia.org/wikipedia/commons/thumb/a/a3/Bial%27s_test.svg/700px-Bial%27s_test.svg.png
  • Mucic acid test: Galactose is treated by nitric acids creates insoluble crystals of mucic acid.
Mucic acid test
Mucic acid test | Source: https://noteshippo.com/wp-content/uploads/2021/07/Capture-20.jpg

6. Osazone formation

Phenylhydrazine, a component of acetic acid when heated with sugars that reduce and forms osazones during an reaction. Based on it, two first carbons (C1 and C2) are the ones involved as part of osazone formation. The sugars that differ in arrangement on these carbons provide the same type of osazones. This is because the differences are concealed by binding to the phenylhydrazine. Therefore, fructose, glucose and mannose are the same kind of (needle-shaped) Osazones. Reduced disaccharides also produce the osazones maltose sunflower and lactose-style powderpuffs.

7. Formation of esters

Monosaccharides’ alcoholic groups are often esterified using either enzymatic or non-enzymatic processes. Esterification of carbohydrate by the phosphoric acid is a typical reaction in the metabolism. The glucose 1-phosphate and glucose 6-phosphate are excellent examples. ATP contributes the phosphate moiety during the formation of ester.

Derivatives Of Monosaccharides

There are many monosaccharides’ derivatives, some of them are essential to our health.

  • Sugar acids: Oxidation of aldehyde or the primary alcohol group of monosaccharides produces sugar acids. Gluconic acid is created by the oxidation process of the aldehyde (C1 group) and glucuronic acids are produced when the principal alcohol group (C6) is converted to C6.
  • Sugar alcoho: Sugar alcohols (polyols)  are created by the reduction of ketoses or aldoses. For example, sorbitol can be created by removing glucose and mannitol, which is derived from mannose.
  • Alditol: The monosaccharides when reduced, give polyhydroxy alcohols that are known as alditols. Ribitol is one of the constituents of flavin coenzymes. Glycerol and myo-inositol form the basis of the lipids. Xylitol is a sweetener that is used in sugar-free gums and sweets.
  • Amino sugars: When one or more hydroxyl group of monosaccharides are substituted by amino-groups, the compounds created include amino sugars e.g. D-glucosamine, D-galactosamine. They are present as constituents of heteropolysaccharides. N-Acetylneuraminic Acid (NANA) is an acetylmannose derivative and the pyruvic acids. It is a key component of glycolipids and glycoproteins. The term”sialic acid” can be utilized to refer to NANA and its derivatives. Certain antibiotics have amino sugars, which could be associated with the activity of antibiotics, e.g. erythromycin.
  • Desoxysugars: They are sugars with one oxygen lower than the one found within the parent molecules. The groups CHOH and Ch2OH are transformed into CH2 and then CH3 because of their absence of oxygen. D-2-Deoxyribose, the most crucial deoxysugar as it’s an essential structural component that is a component of DNA (in contrast to D-ribose found in the RNA). Feulgen staining can detect deoxyribose, which is DNA within tissues. Fucose can be described as a deoxy L-galactose that is found on blood groups antigens as well as certain glycoproteins.
  • L-Ascorbic Acid (vitamin C):  It is a water-soluble vitamin its structure closely is similar to that of a monosaccharide.
Derivatives Of Monosaccharides
Derivatives Of Monosaccharides

Glycosides

Glycosides form by the hemiacetal or the hemiketal hydroxyl groups (of the anomeric carbon) of one carbohydrate is reacted with a carbohydrate’s hydroxyl group or noncarbohydrate (e.g. an ethanol, methyl, or or glycerol). The bond created is known as glycosidic bond , and the non-carbohydrate component (when there is) is called an aglycone.

Monosaccharides are bonded through glycosidic bonds and result as di- or oligo, or polysaccharides (see the next section for details of structures). Naming of glycosidic bonds : The naming of glycosidic bonds relies on the links between carbon atoms as well as the state of the carbon atoms that are anomeric (D or E). For instance, lactose, which is formed by a link between C1 of E-galactose as well as C4 of glucose is referred to as E(1 or 4) glycosidic bond. The other glycosidic bond types are defined within the structure of polysaccharides and disaccharides.

Glycosides
Glycosides

Physiologically important glycosides

  • Glucovanillin (vanillin-D-glucoside) is a natural substance that imparts vanilla flavour.
  • The Cardiac Glycosides (steroidal glycosides) : Digoxin and digitoxin contain the steroid aglycone, and also enhance the contraction of muscles.
  • Streptomycin is an antibiotic that is used to treat tuberculosis, is glycoside.
  • Ouabain hinders Na+ K+ ATPase and stops the transport activity for Na+.
  • Phlorhizin can cause renal damage in laboratory animals.

Examples of Common Monosaccharides

Glucose

The monosaccharide Glucose is found naturally and is widespread. It is able to join with other monosaccharide unit units to create disaccharides, such as maltose (i.e. 2 glucose molecules) as well as lactose (i.e. galactose and glucose molecules) and sucrose (i.e. fructose and glucose molecules).

Glucose is among the photosynthesis products found in plants as well as other photosynthesis organisms. In plants sugar molecules are stored as repeated sugar units (e.g. starch). It is also a key ingredient in amylopectin as well as cellulose. It is found in plant juices, fruits and a variety of other organs of the plant. It is also an important intermediate in the process of cell respiration as well as a significant fuel source (via aerobic or anaerobic respiratory). Animals, glucose circulates within the bloodstream and is called blood sugar. A surplus of glucose can be stored in the form of glycogen.

Galactose

Galactose is akin to glucose in chemical structure. However the directions of OH and H to carbon4 are switched. Like glucose, galactose is not found in its free state. It is usually a component of biomolecules that are complex. For example, galactose in combination with glucose form lactose (milk sugar) which is disaccharide. Lactose is the disaccharide in milk, is composed of galactose that is joined to glucose through an -(1-4) glycosidic bond. Galactose’s jointment with glucose is catalyzed by enzymes lactase as well as b-galactosidas. The catabolism process of Galactose (where glucose is transformed into glucose) is accomplished through the Leloir pathway.

In human lactation one of the main sources of lactose present in breast milk comes from de novo production of galactose and glucose via Hexoneogenesis. In plant species like the axlewood ( Anogeissus latifolia) and acacia trees galactose monomers join to form a polysaccharide that is referred by its name, galactan.

Fructose

Fructose is thought to be the most sweet naturally occurring carbohydrate. Natural sources of fructose include fruit, honey along with sugarcane. The ketonic monosaccharide is as it has the reduced element (carbonyl) on carbon 2. This is different from the glucose (which can be described as an aldose) with its carbonyl group located at carbon 1. The natural plant source of fructose is and fruits, with a particular focus on roots vegetables, and so on. It is found in abundance or bonds to glucose , resulting in sucrose.

Examples of Common Monosaccharides
Examples of Common Monosaccharides | Source: https://s3-us-west-2.amazonaws.com/courses-images/wp-content/uploads/sites/2569/2017/10/23192554/100000000000048B000001F7B1BD883E.png

Metabolic Pathways Involving Monosaccharides

Monosaccharides play a role in a variety of vital metabolic pathways. Some of these pathways include:

  • Glycolysis is the process of converting one monosaccharide to pyruvate and the subsequent production of biomolecules with high energy
  • Pentose phosphate pathway is an alternative route to metabolically the breakdown of glucose
  • It is the process of converting monosaccharides that are not carbohydrate precursors.
  • Glycogenolysis, the breakdown of glycogen storage into monosaccharide units
  • Glycogenesis – the process of turning glucose into glycogen
  • Fructose metabolism is the process in which fructose is the primary ingredient instead of glucose, is able to enter the glycolytic pathway
  • Galactose metabolism is the process by which galactose enters into the glycolytic pathway after being phosphorylated before being transformed into glucose-6-phosphate.

References

  • BeMiller, James N. (2019). Carbohydrate Chemistry for Food Scientists || Monosaccharides. , (), 1–23. doi:10.1016/B978-0-12-812069-9.00001-7 
  • Yahia, Elhadi M. (2019). Postharvest Physiology and Biochemistry of Fruits and Vegetables || Carbohydrates. , (), 175–205. doi:10.1016/B978-0-12-813278-4.00009-9 
  • http://what-when-how.com/glycoconjugates-and-carbohydrates/monosaccharides-part-1-glycoconjugates-and-carbohydrates/
  • https://www.brainkart.com/article/Monosaccharides_27771/
  • https://biochemden.com/monosaccharide-classify/
  • https://theory.labster.com/monosaccharides/
  • https://noteshippo.com/derivatives-of-monosaccharides-functions-and-importance/
  • http://chemistry2.csudh.edu/rpendarvis/monosacch.html
  • https://www.nutrientsreview.com/carbs/monosaccharides-simple-sugars.html
  • https://www.studysmarter.de/en/explanations/biology/biological-molecules/monosaccharides/
  • https://www.toppr.com/guides/chemistry/biomolecule/monosaccharides/
  • https://www.news-medical.net/health/Carbohydrate-Monosaccharides.aspx
  • https://www.biologyonline.com/dictionary/monosaccharide
  • https://biologydictionary.net/monosaccharide/
  • https://www.thoughtco.com/monosaccharide-definition-and-functions-4780495
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Microbiology Notes is an educational niche blog related to microbiology (bacteriology, virology, parasitology, mycology, immunology, molecular biology, biochemistry, etc.) and different branches of biology.

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