How are carbohydrates classified?

Imagine you’re at a candy store, and you see those small, colorful sweets that you can easily pop into your mouth - these are like monosaccharides, the most basic units of carbohydrates. They are simple sugars that cannot be broken down into simpler sugars by hydrolysis. This makes them building blocks for more complex forms of carbohydrates.

Common examples of monosaccharides include glucose, often referred to as blood sugar, fructose, which is found in fruits, and galactose, a component of milk sugar. In terms of structure, these sugars typically have a backbone of three to seven carbon atoms and can exist in linear or ring-shaped forms.

• Glucose: The primary energy source for your body’s cells.
• Fructose: Found in fruits and is the sweetest of the simple sugars.
• Galactose: Usually doesn't occur alone in foods, but as part of the disaccharide lactose.

Stepping up from monosaccharides, we have disaccharides, which are comparable to two pieces of candy stuck together. Disaccharides are carbohydrates made up of two monosaccharide molecules bonded together. They are formed through a crucial reaction known as dehydration synthesis, where a water molecule is removed to join the two sugars.

Some of the well-known disaccharides include sucrose (table sugar), lactose (found in milk), and maltose (present in malted foods and beers). These are important in our diet and metabolism.

• Sucrose: Composed of glucose and fructose, and is what most people think of as 'sugar'.
• Lactose: The sugar found in milk, made of glucose and galactose, which can be hard to digest for some people.
• Maltose: This forms from two glucose molecules and is less common in our diet but important in the brewing process.

Imagine you have a long necklace of beads; this represents polysaccharides - the complex carbohydrates formed when more than two monosaccharide units are linked together. Unlike the simple sugars, polysaccharides can consist of hundreds to thousands of monosaccharide units and serve various functions in living organisms.

They can be storage forms of energy, like starch in plants and glycogen in animals, or serve structural purposes, like cellulose in the cell walls of plants.

• Starch: The way plants store glucose, which humans digest into glucose for energy.
• Glycogen: How animals, including humans, store excess glucose which can be converted back when needed for energy.
• Cellulose: A major component of plant cell walls, which humans cannot digest but plays an important role in dietary fiber.

Imagine building a toy with snap-together bricks - this is similar to dehydration synthesis, where two molecular 'pieces' join together, and in the process, a water molecule is snapped off and released. In carbohydrate chemistry, dehydration synthesis, also known as a condensation reaction, is fundamental to constructing disaccharides and polysaccharides from monosaccharide units.

During this reaction, one monosaccharide loses a hydroxyl group (–OH) while the other loses a hydrogen (–H), combining to form water (H₂O) and resulting in the formation of a covalent bond between sugar units.

Dehydration reactions are not limited to sugars; they’re also vital in forming proteins and nucleic acids, making them a cornerstone of biochemical processes.