What are Monosaccharides?
Monosaccharides or simple sugars are any of the basic compounds that serve as the building blocks of carbohydrates. The structure of monosaccharides is formed with more than one hydroxyl group (-OH) and a carbonyl group (-C=O) either at the terminal carbon atom known as an aldose or at the second carbon atom known as a ketose. Molecules with such structures are called polyhydroxy aldehydes or ketones.
Monosaccharides are classified by the number of carbon atoms present in the molecule:
Dioses have two
Trioses have three
Tetroses four
Pentoses five
Hexoses six
Heptoses seven.
These different Monosaccharides can be found combined as xylem in woody materials or as arabinose from coniferous trees even in our body as ribose, a component of ribonucleic acids (RNA) and several vitamins.
Nomenclature:
The nomenclature of monosaccharides is regulated by international rules. The common names for the carbohydrates are used together with the type of anomalism, cyclic form, D- series, L- series, and the rotatory power. A few examples for this kind of nomenclature are α-D (+)-glucopyranose, 2-amino-2-deoxy-D (+)-glucopyranose.
A few initials have been adopted to facilitate the writing some of the common names for that are Glc: glucose; Gal: galactose; Man: mannose; Fuc: fucose; Xyl: xylose; Ara: arabinose; Rha: rhamnose; GlcN: glucosamine; GlcNAc: N- acetyl-glucosamine; Mur NAc: N-acetylmuramic acid; Glc AU: glucuronic acid; NeuAc: N-acetylneuraminic acid.
Uses of monosaccharides:
Several derivatives of monosaccharides are important for different requirements. Ascorbic acid (vitamin C) is derived from glucose. Important sugar alcohols (alditols), formed by the reduction of (i.e., in addition of hydrogen to) a monosaccharide, include sorbitol (glucitol) from glucose and mannitol from mannose; both are used as sweetening agents. Glycosides derived from monosaccharides are abundant and found almost everywhere, especially in plants.
Types of Monosaccharides are as follows:
Neutral monosaccharides
Osamines
Uronic acids
Sialic acids
Neutral Monosaccharides
They include the carbohydrates which contain only an alcohol group with their ketone and aldehyde group. Examples: D-glucose, D-galactose, D-mannose, D-xylose. The Deoxys, which are monosaccharides having lost 1 or 2 oxygen atoms also are included in this type of monosaccharides.
Osamines:
They are derived from neutral monosaccharides. The neutral monosaccharides hydroxyl (generally the one carried by carbon 2) is replaced by an amine group.
Uronic acid:
Uronic acids are derived from aldoses by oxidation of the primary- alcohol group into a carboxylic group (and therefore maintain the aldehyde group). D-Glycuronic (also called “glucuronic”) acid.
Sialic acids:
Sialic acids are derivatives of neuraminic acid which consists of a molecule of pyruvic acid which then is condensed with a molecule of D-monoamine.
These acids are constituents of various glycoproteins and glycolipids.
To understand the concept of monosaccharides better you must know the physical and chemical properties of monosaccharides. The students are advised to understand these properties properly as the questions asked will be based on these few properties of monosaccharides.
Physical properties:
Monosaccharides dissolve in water and give a sweet taste.
They are all able to pass through a plasma membrane.
The monosaccharides are soluble in water as when they dissolve in water they take up aring-like form which is the main cause for their solubility in water.
The lowering of water potential can be initiated by dissolving monosaccharides in water.
Chemical properties:
Formation of ethers
Alkylation
Oxidation of monosaccharides
The action of concentrated acids
The action of Phenyl hydrazine
Action of alcohols
Elements of Monosaccharides
Monosaccharides fill two principal roles in the cell. They are utilized to store and create energy.
Glucose is an especially significant energy particle. Energy is delivered when a compound bond is broken.
Monosaccharides are likewise utilized as a part to make more perplexing sugars, which are significant underlying parts.
Properties of Monosaccharides
In an unadulterated structure, monosaccharides are glasslike, water-solvent, boring solids. Monosaccharides are sweet on the grounds that the direction of the OH bunches is associated with the taste receptors on the tongue to perceive pleasantness. Because of the lack of hydration response, two monosaccharides structure disaccharides, 3 to 10 oligosaccharides, and at least 10 polysaccharides.
Principle Discoveries: Monosaccharides
Monosaccharides are the littlest starch particles. They are additionally called monosaccharides since they can't be separated into less complex sugars.
Instances of monosaccharides incorporate glucose, fructose, ribose, xylose, and mannose.
The two principal elements of monosaccharides in the body are energy stockpiling and complex sugars utilized as underlying parts as parts.
Monosaccharides are water-dissolvable, normally sweet-tasting glasslike solids.
More with regards to Monosaccharides
Monosaccharides are starch particles and can't be hydrolyzed into less complex (more modest) sugar atoms. Accordingly, monosaccharides are once in a while alluded to as "monosaccharides" or just sugars.
This recommends that monosaccharides are the least complex (least) sugars. (The term sugar stick comes from the old sugar stick term sucrose.
It currently applies to all sugars, particularly monosaccharides. Notwithstanding, it very well may be applied to sugars, everything being equal, as the following part on oligosaccharides and polysaccharides shows.
The thing comes from one of the Greek words. In science, the term monosaccharide implies sugar or sugar, which implies that it is a particle that comprises just one sugar unit and no at least two sugar units are bound to it).
Monosaccharides are monomeric units of oligosaccharides and polysaccharides, the two of which contain numerous (sugar) units and can be hydrolyzed to deliver the constituent monosaccharides.
Common monosaccharides utilized as a part of oligosaccharides and polysaccharides in food sources incorporate a gathering called the sucrose bunch.
Starches (a term derived from French hydrate decarbonizer like German sugars) have the essential piece Cx (H2O) y (that is, they contain carbon and hydrogen, oxygen iotas, which are normal to most basic carbs). Addresses the way that it has an atom that contains). ) At a similar rate as it happens in water). Their piece is associated with the way that they are composed of carbon dioxide and water by photosynthesis, as shown by the accompanying imbalanced condition.
CO2 + H2O → sugar + O2
Nonetheless, It has been seen that a large portion of the normal carb found in living beings don't have the straightforward exact recipe Cx (H2O) y. Rather, the most normally happening carbs are oligomers (oligosaccharides) or polymers (polysaccharides) made by consolidating sugars with basic observational equations, or basically altered sugars related with straightforward exact recipes.
Low sub-atomic weight carbs for food frequently get from the depolymerization of regular macromolecules, yet the book starts with an outline of monosaccharides, from which it is incorporated into bigger, more mind-boggling structures.
Starches (additionally called sugars) are described by the way that they contain chiral carbon molecules.
Chiral carbon molecules are carbon particles that can exist in two diverse spatial plans (developments).
Chiral carbon particles are not difficult to perceive on the grounds that every one of the four tetrahedral bonds is a carbon iota clung to an alternate molecule or gathering of iotas.
Two unique game plans (organizations) of the four gatherings of rooms are supposed to be identical representations that can't be overlaid.
A few Derived Compounds from Monosaccharides are as follows:
1. L-Ascorbic Acid (Vitamin C):
A study of its structure revealed that it is the γ-lactone of a hexatonic acid, which itself derives from an aldohexose by oxidation of the aldehyde group to acid. It is further characterized by a double bond between 2 carbon atoms, each carrying a hydroxyl (enediol). L-Ascorbic Acid (Vitamin C) substance readily oxidized to dehydroascorbic acid, which enables its participation in cellular oxidation-reduction processes.
2. Polyalcohol (or Polyols):
Reduction of the aldehyde or ketone group to the alcohol group gives us a carbohydrate called Polyalcohol. There is a type of Polyalcohol or cyclic polyalcohol, called cyclitols. The representative of this group most frequently found in nature is Myo-inositol, it is present either in the Free State or Hexa-esterified by phosphoric acid or as a constituent of certain phospholipids, the phosphatidylinositol.
A few more Derivatives of Monosaccharides are mentioned below:
Amino sugars such as:
Galactosamine
Glucosamine
Sialic acid
N-Acetyl Glucosamine
Sulfa Sugars such as:
Sulfoquinovose
Others
Ascorbic acid
Mannitol
Glucuronic acid.
Isomerism of Monosaccharides:
The isomerism in monosaccharides is a very important phenomenon. But before we try to understand isomerism in monosaccharides we first need to understand the general meaning of the term isomerism.
It is a phenomenon where two or more compounds have the same chemical formula but possess different structural formulas and different properties. Isomers are compounds exhibiting isomerism. The isomerism in monosaccharides works similarly.
When we consider the projection of the three-dimensional structure of any monosaccharide we find that there are 2 possibilities. For example, if we take glyceraldehyde; in one case, the hydroxyl carried by the carbon next to the primary alcohol group (this carbon atom is called asymmetric because it carries 4 different types of substitutes and is indicated by an asterisk) is situated to the right of the plane formed by the carbon chain; this is the D-configuration; in the other case, the hydroxyl is situated to the left of this plane; this is the L-configuration.
These two forms are mirror images that practically have the same chemical properties but their structure is different from each other.
The Aldoses and Ketoses can be summarized and explained in the following way:
Carbohydrates can be divided into two parts: polyhydroxy aldehydes, the aldoses, or polyhydroxy ketones, the ketoses.
For a carbohydrate to be termed as an aldose it needs an aldehyde group.
Aldehyde groups can be written as CH=O, and are also often written as CHO.
For a carbohydrate to be a ketose it needs to have a ketone group.
The chiral centers are always marked with an asterisk mark or ‘*'.
The assignment of molecules is very apparent in the acyclic form of the sugars.
To find an aldose or a ketose, in a cyclic form first find the anomeric center (*). The Substituents on that are to be taken care of; if one of them is an H then it is an aldose.
The systems can be further classified based on how many C atoms there are:
O4 C = tetrose
O5 C = pentose
O6 C = hexose
Cyclic structures of Monosaccharides:
Knowing the cyclic structure of the monosaccharides is very important, as, like the melting point or boiling point, the rotatory power is a constant characteristic of a substance, and this change must reflect a structural modification.
The conversion of monosaccharides from linear to cyclic occurs due to their reaction with alcohols. Monosaccharides that contain five or more carbon atoms form cyclic structures, in an aqueous solution. Two cyclic stereoisomers can form from straight-chain monosaccharides that will be known as anomers. An equilibrium mixture forms between the two anomers, and the straight-chain structure of a monosaccharide, in an aqueous solution. This process is known as mutarotation.
The difference between α and β forms of sugars must seem trivial, but such structural differences are often very important in biochemical reactions. How energy is obtained from the starch in potatoes and other plants but not from cellulose, although both starch and cellulose are polysaccharides that are composed of glucose molecules linked together are explained by this.
A few questions that can be asked in the theory exams can be as follows:
1. Define each term.
Mutarotation
Anomer
Anomeric carbon
2. How can you prove that mutarotation is exhibited by a solution of α-D-glucose?
3. Explain the reduction of aldoses and the reduction of ketoses in detail.
4. Mention a few structural importance of sugars and the basic physical properties of Monosaccharides.
5. Explain all the chemical properties of monosaccharides and make sure you write the reactions of every property as well with a proper description by using an example. To test if you understood the concept properly or not the students are advised to solve the few exercises given below:
Draw the cyclic structure for β-D-glucose. Identify the anomeric carbon.
Draw the cyclic structure for α-D-fructose. Identify the anomeric carbon.
Draw the cyclic structure for α-D-mannose for a given aldohexose D-mannose that differs from D-glucose at the second carbon atom only in the configuration.
Draw the cyclic structure for β-D-allose for a given aldohexose D-allose that differs from D-glucose at the third carbon atom, only in the configuration.
The types of multiple-choice questions that can be asked are also given below:
1. Glucose is a monosaccharide and is a
Hexose
Pentose
Furanose
Sucrose
2. The simplest form of sugars is usually
Colorless
Water-soluble
Crystalline
All of the above
3. The formula for monosaccharides is
(CH2O)n
CnH2n
Both A and B
None of the above
4. A monosaccharide switches from an open-chain to a cyclic form through
Hydroxylation
Nucleophilic addition
Hydrogenation.
FAQs on Monosaccharides
1. What are monosaccharides and why are they called simple sugars?
Monosaccharides are the most basic form of carbohydrates and are often called simple sugars because they cannot be broken down (hydrolysed) into smaller carbohydrate units. Structurally, they are polyhydroxy aldehydes or ketones, meaning they consist of a carbon chain with multiple hydroxyl (-OH) groups and one carbonyl (C=O) group. Their simplicity makes them the fundamental building blocks for more complex carbohydrates.
2. What is the general chemical formula for monosaccharides?
The general chemical formula for most monosaccharides is Cn(H2O)n, where 'n' represents the number of carbon atoms. This formula indicates that for every carbon atom, there are atoms of hydrogen and oxygen in the same ratio as in water. Typically, 'n' ranges from 3 to 7 for common monosaccharides.
3. How are monosaccharides classified?
Monosaccharides are classified in two primary ways:
- Based on the number of carbon atoms: They are named using a prefix that indicates the carbon count, such as trioses (3 carbons), tetroses (4 carbons), pentoses (5 carbons), and hexoses (6 carbons).
- Based on the functional group: They are classified as either an aldose (containing an aldehyde group, -CHO) or a ketose (containing a ketone group, C=O). For example, glucose is an aldohexose, while fructose is a ketohexose.
4. What is the key difference between an aldose and a ketose sugar?
The key difference lies in the location of the carbonyl group (C=O). In an aldose, the carbonyl group is at the end of the carbon chain, forming an aldehyde group. An example is glucose. In a ketose, the carbonyl group is located at any other position within the carbon chain, forming a ketone group. An example is fructose, where the C=O group is on the second carbon atom.
5. What are some common examples of monosaccharides and their natural sources?
Some of the most common and important monosaccharides include:
- Glucose: Often called blood sugar, it is the primary energy source for cells and is found in fruits, honey, and as the building block of starch and cellulose.
- Fructose: Known as fruit sugar, it is found in fruits, honey, and vegetables. It is one of the sweetest naturally occurring sugars.
- Galactose: This monosaccharide is a component of lactose, the sugar found in milk and dairy products.
6. What are the primary functions of monosaccharides in living organisms?
Monosaccharides serve two principal roles in biological systems:
- Energy Source: They are the primary fuel for cellular respiration. Glucose, in particular, is broken down to produce ATP, the main energy currency of the cell.
- Structural Components: They act as monomeric units or building blocks for larger, more complex carbohydrates. For instance, ribose and deoxyribose are pentose sugars that form the backbone of RNA and DNA, respectively.
7. Why do most monosaccharides form cyclic structures in aqueous solutions instead of remaining as open chains?
In an aqueous solution, the open-chain form of a monosaccharide (especially those with five or more carbons) is unstable. An intramolecular reaction occurs where a hydroxyl group attacks the carbonyl carbon. This reaction forms a stable cyclic hemiacetal (in aldoses) or cyclic hemiketal (in ketoses). This ring structure is energetically more favourable than the linear form, and an equilibrium is established in the solution, with the vast majority of molecules existing in the cyclic form.
8. How do monosaccharides, disaccharides, and polysaccharides differ from each other?
The primary difference among these carbohydrate types is the number of sugar units they contain:
- Monosaccharides: Consist of a single sugar unit (e.g., glucose, fructose).
- Disaccharides: Composed of two monosaccharide units joined by a glycosidic bond (e.g., sucrose, which is glucose + fructose).
- Polysaccharides: Are polymers made of many monosaccharide units linked together (e.g., starch and cellulose, which are polymers of glucose).
9. What determines if a monosaccharide has a D or L configuration?
The D or L configuration is determined by the spatial arrangement of the hydroxyl (-OH) group on the chiral carbon atom that is farthest from the main carbonyl group. When drawing the molecule in a Fischer projection:
- If the -OH group on this specific carbon is on the right, the sugar is designated as a D-isomer.
- If the -OH group is on the left, it is designated as an L-isomer.
Most naturally occurring sugars in biological systems, such as D-glucose, are in the D-configuration.
10. What are anomers, and how does this concept apply to the structure of glucose?
Anomers are specific types of stereoisomers found in cyclic monosaccharides. They differ only in the configuration at the new chiral centre that is formed upon cyclisation, known as the anomeric carbon (which was the original carbonyl carbon). For glucose, this results in two anomers:
- α-D-glucose: The hydroxyl group on the anomeric carbon is on the opposite side of the ring from the -CH2OH group.
- β-D-glucose: The hydroxyl group on the anomeric carbon is on the same side of the ring as the -CH2OH group.
11. In which common foods can a student find monosaccharides like glucose and fructose?
Monosaccharides are naturally present in many foods and are also products of digestion. Key sources include:
- Fructose: Abundantly found in fruits (like apples, grapes), honey, and root vegetables (like beets and carrots).
- Glucose: Found in honey and some fruits. More importantly, it is the building block of starches, so foods like potatoes, rice, and bread provide glucose after being broken down by the digestive system.
