Lesson 5 – Carbohydrates (Part 2)

Projections of Sugar Structures

When we study the structure of sugar molecules (like glucose), there are two common ways scientists draw them to understand their shape and how the atoms are connected. These drawings are called “projections”.

📌 1. Fischer Projection

• Named after a German chemist, Emil Fischer, who created this in 1891.
• It shows the sugar molecule in its open-chain (straight-line) form, not in a ring shape.
• Think of it like this: If you imagine unfolding a bracelet into a straight wire — that’s how a sugar ring looks in the Fischer projection.

Real-life analogy: Imagine a beaded necklace that’s been straightened out flat — that’s like a Fischer projection of a sugar!

📌 2. Haworth Projection

• Named after Sir Norman Haworth, a British chemist.
• This projection shows the cyclic (ring) form of sugars, which is how sugars exist in water most of the time.
• In this model, the sugar “closes” into a ring like a bracelet.

Real-life analogy: Just like a belt is used in a circle around your waist, many sugar molecules form a circular ring structure — this is the Haworth projection.

2. Disaccharides (Double Sugars)

✅ Definition and Formation

• Disaccharides are made by joining two monosaccharides (simple sugars).
• This joining happens through a special reaction called dehydration synthesis, where a water molecule is removed to form a bond.

🧪 Glycosidic Bond:
This is the special covalent bond (strong chemical link) that forms between two sugar molecules.

🌀 Hydrolysis:
When we want to break this bond and split the disaccharide into two monosaccharides, we add water — this process is called hydrolysis.

💧 Mnemonic for Formation and Breakdown:

“Dehydration makes them bond, Hydrolysis breaks the bond.”

📉 Solubility

• Disaccharides are less soluble in water than monosaccharides. That means they don’t dissolve as easily.

🌟 Physiologically Important Disaccharides

Let’s explore three important disaccharides that you might hear about in daily life.

🧁 1. Maltose (Malt Sugar)

• Made from: Two glucose molecules.
• Bond: The two glucose units are joined with a 1,4-glycosidic bond.
  • This means carbon 1 of the first glucose is connected to carbon 4 of the second one.
• Where it is found: In cereals like wheat, corn, and barley.
• How it is formed: It’s an intermediate product when our body digests starch (like bread or rice).

📌 Real-life analogy:
Think of maltose like two friends (two glucose molecules) holding hands (glycosidic bond) while walking through a cereal field!