2.1. Definition

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

Carbohydrates are a type of biomolecule that can be identified as either polyhydroxy aldehydes or ketones. This means they contain multiple hydroxyl (-OH) groups and one aldehyde or ketone group. They are important because, when they undergo hydrolysis (a chemical reaction involving water), they break down into simpler sugars, which are crucial for providing energy to living organisms.

Think of carbohydrates like a multi-layered cake. When you cut and serve the cake, you access the individual layers (or sugars). In this analogy, the layers represent the complex carbohydrates that break down into simpler forms when consumed.

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 can be grouped into three main types: monosaccharides, oligosaccharides, and polysaccharides.

• Monosaccharides are the simplest form and cannot be broken down into smaller sugars. Examples include glucose and fructose.
• Oligosaccharides consist of 2 to 10 monosaccharides linked together and can include sugars such as sucrose and lactose.
• Polysaccharides are long chains of monosaccharides, which can include starch and cellulose, and serve as energy storage or structural components in cells.

Imagine you have a set of stacking blocks. Each individual block represents a monosaccharide. When you connect several blocks together, you're creating an oligosaccharide. Finally, when you assemble a large tower of blocks, you're forming a polysaccharide. This illustrates how simple sugars can combine to create more complex carbohydrate structures.

• Simplest sugars with the general formula Cₙ(H₂O)ₙ. • Classified as aldoses (with an aldehyde group) or ketoses (with a ketone group). Examples: • Glucose (aldohexose) • Fructose (ketohexose)

Monosaccharides are the most basic units of carbohydrates. They can be classified based on the presence of specific functional groups:

• Aldoses contain an aldehyde group, while ketoses have a ketone group.
• They generally follow the formula Cₙ(H₂O)ₙ, indicating that they are composed of carbon, hydrogen, and oxygen atoms. Common examples are glucose, which is an aldohexose (six carbons with an aldehyde), and fructose, which is a ketohexose (six carbons with a ketone).

Consider monosaccharides like pieces of fruit. Just as a single apple or a single pear can represent a component of a salad, monosaccharides are the individual pieces that combine to form larger carbohydrate structures. Each type of fruit has its unique taste and characteristics, similar to how aldoses and ketoses have different chemical properties.

Glucose (C₆H₁₂O₆) • Most important sugar in biology. • Found in honey, fruits. • Prepared by hydrolysis of starch. • Exists in cyclic (α and β) forms.

Glucose is vital in biology, functioning as a primary energy source for cells. It has the chemical formula C₆H₁₂O₆, which sums up its six carbon atoms, twelve hydrogen atoms, and six oxygen atoms. Glucose is naturally found in foods like honey and fruits and can also be produced from starch through hydrolysis. Furthermore, glucose can exist as two different cyclic forms called alpha (α) and beta (β), which differ in the orientation of one of the hydroxyl groups.

Imagine glucose as a currency that fuels currency exchanges, similar to how money is crucial for transactions. In our bodies, glucose acts like this currency, providing energy that is exchanged for fuel whenever our cells perform activities. Whether it comes from fruits in our diets or is made from starch, glucose is always at the center of the energy economy in our body.

• Formed by glycosidic linkage between two monosaccharide units. Examples: • Sucrose = Glucose + Fructose • Lactose = Glucose + Galactose • Maltose = Glucose + Glucose

Disaccharides are carbohydrates formed when two monosaccharide molecules bond together through a process called glycosidic linkage. This connection is important because it allows different types of simple sugars to form more complex sugars. For example, sucrose (table sugar) is made of glucose and fructose, lactose is formed from glucose and galactose, and maltose consists of two glucose molecules. This bonding is essential for the formation of many sugars we encounter in our diets.

Consider disaccharides like a pair of friends teaming up to complete a project. Just as the combined efforts of two different people can produce greater results, two monosaccharides come together to create a disaccharide, resulting in new flavors and functions in foods we consume, like how sucrose sweetens our tea.

• Long chains of monosaccharide units. Examples: • Starch – Storage carbohydrate in plants. • Cellulose – Structural component in plant cell walls. • Glycogen – Storage carbohydrate in animals.

Polysaccharides are large, complex carbohydrates made up of long chains of monosaccharide units. They serve various functions in organisms: starch acts as an energy storage form in plants, cellulose provides structural support in plant cell walls (making up the fibers in our diet), and glycogen serves a similar energy storage role in animals but is readily available for quick energy use when needed. These features highlight the diversity of roles that polysaccharides play in living organisms.

Think of polysaccharides as living libraries filled with information. Just like books in a library contain extensive knowledge, polysaccharides store energy and information critical for life processes. Each type (like starch, cellulose, and glycogen) represents a different section that serves a unique purpose in the 'library' of life.

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