Monosaccharides

• Monosaccharides are organic compounds with unbranched carbon chains.
• Monosaccharides are defined as mono means “one” and saccharides mean “sugars”.
• They are simple sugars, sweet in taste, and soluble in water.
• They polyhydroxy aldehyde or ketone with formula (CH2O)n. This means monosaccharides are composed of carbon, hydrogen, and oxygen. The number of carbon and oxygen are the same and the hydrogen number is twice the carbon number.
• They are the simplest carbohydrates.
• They cannot be hydrolyzed into simple sugar units on hydrolyzes.

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Classification

Monosaccharides are classified based on the number of carbon atoms and functional groups they contain.

Based on the carbon atom

Trioses ( C3H6O3 )

Tetroses ( C4H8O4 )

Pentoses ( C5H10O5 )

Hexoses ( C6H12O6 )

Heptoses ( C7H14O7 )

Based on functional group

Aldoses (sugars which contain aldehyde functional group)

Ketoses (sugars which contain ketone functional group)

Structure

All monosaccharides contain a carbon chain as a backbone, each carbon attaches to oxygen either with a single bond or a double bond. All carbon makes single bonds to oxygen only one makes double bonds either as an aldehyde (if present at the terminal carbon atom) is aldoses, or keton (if present at the central carbon atom) is ketoses.

For. For example:

In glucose (an aldohexose), there are six carbon atoms (hexose) with a carbonyl group at carbon 1 (C1), forming an aldehyde. The other five carbons are attached to hydroxyl groups (-OH). Fructose, on the other hand, is a ketohexose, where the carbonyl group is at carbon 2 (C2), forming a ketone.

Example

Glucose

Glucose is a fundamental monosaccharide, widely recognized for its pivotal role in biological systems. As a six-carbon sugar, it serves as a primary source of energy in organisms ranging from bacteria to humans. Found abundantly in nature, glucose is a key component of carbohydrates like starch and cellulose, crucial for plant structure and energy storage.

In human metabolism, glucose plays a central role as the primary fuel for cellular respiration, providing energy for vital physiological processes. Its versatility extends beyond energy production; glucose serves as a building block for larger carbohydrates like glycogen and is a foundational component of disaccharides such as sucrose and lactose. Its regulation in the bloodstream is tightly controlled to maintain optimal health, making glucose not only essential for immediate energy needs but also for long-term storage and structural integrity in biological systems.

Fructose

Fructose is a monosaccharide that plays a significant role in human nutrition and metabolism. It is commonly known as fruit sugar due to its high concentration in fruits and honey. Structurally similar to glucose, fructose is also a six-carbon sugar but differs in its metabolic pathway and sweetness. While glucose is metabolized throughout the body, fructose is primarily metabolized in the liver, where it can be converted into glucose or stored as glycogen for future energy needs. Its intense sweetness, about 1.7 times sweeter than glucose, makes it a popular sweetener in the food industry, often used in beverages, processed foods, and desserts.

However, excessive consumption of fructose, particularly in the form of high-fructose corn syrup, has been linked to metabolic disorders such as obesity and insulin resistance. Despite these concerns, fructose remains an essential component of the human diet when consumed in moderation through natural sources like fruits, contributing to overall nutritional balance and dietary diversity.

Galactose

Galactose is a monosaccharide that, along with glucose, forms the disaccharide lactose, commonly known as milk sugar. Structurally similar to glucose and fructose, galactose is a six-carbon sugar that plays a crucial role in biological processes and nutrition. It is primarily obtained through the digestion of lactose-containing dairy products such as milk, yogurt, and cheese. In the body, galactose is metabolized into glucose through a series of enzymatic reactions, primarily occurring in the liver. This conversion process is essential for providing energy to cells and tissues throughout the body.

Galactose also contributes to the structure of complex carbohydrates like glycolipids and glycoproteins, which are important components of cell membranes and signaling molecules. While deficiencies in enzymes required for galactose metabolism can lead to rare genetic disorders such as galactosemia, in normal physiological conditions, galactose serves as a vital nutrient contributing to overall health and energy metabolism.