1.1. Definition

Carbohydrates are polyhydroxy aldehydes or ketones or compounds that yield such products upon hydrolysis.

Carbohydrates are organic molecules characterized by the presence of multiple hydroxyl groups (-OH) and a carbonyl group (either an aldehyde or a ketone). Polyhydroxy refers to the presence of many hydroxyl groups. When these carbohydrates are broken down through a chemical reaction called hydrolysis, they yield simpler molecules such as aldehydes or ketones, which are fundamental structures in organic chemistry.

You can think of carbohydrates like a complex Lego structure. When you pull apart the pieces (like in hydrolysis), you can create simpler shapes (like aldehydes or ketones), which can be reassembled in different ways.

Carbohydrates are classified based on their hydrolysis behavior:

1. Monosaccharides – Cannot be hydrolysed further (e.g., glucose, fructose).
2. Oligosaccharides – Yield 2–10 monosaccharide units on hydrolysis (e.g., sucrose, lactose).
3. Polysaccharides – Yield many monosaccharides on hydrolysis (e.g., starch, cellulose).

Carbohydrates are categorized into three main classes based on how they can be broken down:

1. Monosaccharides are the simplest form and cannot be further hydrolyzed. They include sugars like glucose and fructose.
2. Oligosaccharides contain a small number of monosaccharide units, typically between two and ten. Examples include sucrose and lactose, which are composed of one or two monosaccharides linked together.
3. Polysaccharides are complex carbohydrates made up of numerous monosaccharide units, such as starch and cellulose, which can be hydrolyzed into many sugar molecules.

Think of carbohydrates like a necklace made of beads. Each bead can represent a monosaccharide (like glucose), while a small group of beads strung together would be like an oligosaccharide, and a long chain of many beads would represent a polysaccharide.

• Simplest sugars with the general formula Cₙ(H₂O)ₙ. • Classified as aldoses (with an aldehyde group) or ketoses (with a ketone group).

Monosaccharides are basic units of carbohydrates and are recognized by their formula, which indicates they are composed of carbon (C), hydrogen (H), and oxygen (O) in a specific ratio (Cₙ(H₂O)ₙ). These sugars can be organized into two categories:

• Aldoses: Monosaccharides that contain an aldehyde group. An example is glucose.
• Ketoses: These feature a ketone group, such as fructose.

Imagine you have building blocks where one type (aldoses) has a unique flag at one end (the aldehyde), and the other type (ketoses) has a star sticker (the ketone). Each type represents different monosaccharides, and depending on the flag or sticker, you classify them accordingly.

Examples: • Glucose (aldohexose) • Fructose (ketohexose)

Glucose and fructose are common examples of monosaccharides:

• Glucose (aldohexose) is crucial in biology as it serves as an important energy source. It is commonly found in fruits and honey.
• Fructose (ketohexose) is also a sugar found in many plants and is known for being sweeter than glucose.

Think of glucose as a staple food item, like rice, providing energy for activities. Fructose, on the other hand, is like dessert, sweeter and often used in snacks and candies due to its higher sweetness.

• Most important sugar in biology. • Found in honey, fruits. • Prepared by hydrolysis of starch. • Exists in cyclic (α and β) forms.

Glucose is considered the most significant sugar in biological systems because it is a primary energy source for cells. It naturally occurs in honey and various fruits. Glucose can also form from the breakdown of starch, which is a polysaccharide. Moreover, glucose can exist in different structures: open-chain form and cyclic forms known as α (alpha) and β (beta) depending on the orientation of the hydroxyl group at carbon 1.

Think of glucose as currency for your body's energy. Just like how you can have different denominations of money (like coins or bills), glucose has different forms that it can take, being versatile for different purposes in your body.

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