Monosaccharides (glucose)

What are Monosaccharides?

Monosaccharides are poly- hydroxy-aldehydes or -ketones, generally with an unbranched C-chain. A carbohydrate is an organic compound with the formula (CH2O), with n > 3.

Monosaccharides are the most basic form of carbohydrates. Most organisms produce and store energy by breaking down the monosaccharides glucose and harvest the energy released. This type of glucose are classified in terms of the number of carbon atoms and also the functional group attached to it. The monosaccharide which contains aldehyde is known as aldose and those which contain a ketone group is known as a ketose.

Where can we find Glucose?

Glucose occurs in both combined as well as in the free state in nature. We can find this in sweet fruits and in honey. Glucose present in ripe grapes in a large amount.

Monosaccharides (glucose)

Structure of Glucose

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Structure of Monosaccharides

All the monosaccharides have the formula as (CH2O) n. Here, the two hydrogen atoms and one oxygen atom associate itself to the central carbon molecule. A hydroxyl group is formed when oxygen will bond with hydrogen. Several carbon molecules bond together because 4 bonds can form on carbon.

One of the carbon will form a double bond with oxygen in the chain, which is termed as a carbonyl group. Depending upon its position, if it is formed at the end of the chain, then, the monosaccharides are said to belong to the aldose family and if it formed in the middle of the chain, then it belongs to the ketose family.

Preparation of Glucose

1. From sucrose (cane sugar): We get glucose and fructose in exactly equal amounts if sucrose is boiled with dilute HCl and H2SO4 in an alcoholic solution.

C12H22O11(Sucrose)+ H2O → C6H12O6 (Glucose)+ C6H12O6 (Fructose)

2. From Starch: When hydrolysis of starch is carried out in boiled and diluted H2SO4 at 393 K under pressure, we get glucose.

(C6H10O5)n (Starch or cellulose) + nH2O + H+ → nC6H12O6 (Glucose)

Examples of Monosaccharides

1. Glucose

Glucose molecules can be broken down by glycolysis in the process of cellular respiration. Glucose can be connected in long strings of monosaccharides to form polysaccharides. In plants, this thing is produced as cellulose. In plants, each cell is surrounded by cellulose that helps plants stand tall and turgid.

2. Fructose

Fructose belongs to the ketose group. Differently shaped monosaccharides break down the specific enzyme. If fructose, combines with other monosaccharides then they form oligosaccharides. Sucrose has a fructose molecule joined with a glucose molecule with the help of a glycosidic bond.

3. Galactose

Galactose is produced by mammals in the form of milk. Lactose holds a lot of energy in its bonds and for breaking down the bonds apart, specific enzymes are developed by offsprings of mammals.

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