Compound A gives D-galactose and D-glucose on hydrolysis. The compound A is
(a) amylose
(b) sucrose

Q: What is hydrolysis?

Hydrolysis is a chemical reaction where water is used to break down the bonds of a particular substance. In carbohydrates, it breaks the glycosidic bonds between monosaccharides.

Q: Why doesn't sucrose give galactose?

Sucrose is formed by the linkage of glucose and fructose. Therefore, its hydrolysis will only yield glucose and fructose, not galactose.

Q: What is the difference between maltose and lactose?

Maltose is a disaccharide made of two glucose units, whereas lactose is made of one galactose unit and one glucose unit.

Q: Is amylose a disaccharide?

No, amylose is a polysaccharide. It is a linear polymer made of many D-glucose units linked together.

Q: What type of linkage is present in lactose?

Lactose contains a $\beta$-1,4-glycosidic linkage between the C1 of $\beta$-D-galactose and the C4 of $\beta$-D-glucose.

Question

Compound A gives D-galactose and D-glucose on hydrolysis. The compound A is

Options:

(A) amylose

(B) sucrose

(C) maltose

(D) lactose

Sigma Percentile · Accepted Answer

### Analyzing the Setup

Imagine you are a molecular detective, and your job is to identify a mystery compound, let's call it **Compound A**. The only clue you have is that when you break it down using water—a process known as **hydrolysis**—it splits into two specific building blocks: **D-galactose** and **D-glucose**.

Hydrolysis is essentially the chemical equivalent of taking a pair of scissors to the bonds that hold complex sugars together. These bonds are called **glycosidic linkages**. By adding water and a little bit of acid as a catalyst, we can snap these linkages and reveal the fundamental monosaccharides that make up the larger molecule.

### Investigating the Suspects

Let's interrogate our four suspects one by one to see which one matches our clue.

First up is **amylose**. Amylose is a long, linear polymer, like a long chain of identical beads. Every single bead in this chain is a **D-glucose** molecule. So, if we hydrolyze amylose, we will only get a massive pile of D-glucose. Since there is no D-galactose to be found here, amylose is innocent.

$$ 	ext{Amylose} + H_2O \xrightarrow{H^+} n 	ext{ D-glucose} $$

Next, we have **sucrose**, which is the common table sugar you might put in your tea. Sucrose is a disaccharide, meaning it's made of exactly two beads. These beads are **D-glucose** and **D-fructose**. When we hydrolyze sucrose, we get one of each. Still no D-galactose! So, sucrose is also off the hook.

$$ 	ext{Sucrose} + H_2O \xrightarrow{H^+} 	ext{D-glucose} + 	ext{D-fructose} $$

Our third suspect is **maltose**. Maltose is another disaccharide, often found in germinating grains. It is formed by linking two **D-glucose** units together. Naturally, breaking it apart will just give us two molecules of D-glucose. Again, this doesn't match our clue.

$$ 	ext{Maltose} + H_2O \xrightarrow{H^+} 	ext{D-glucose} + 	ext{D-glucose} $$

### The Final Reveal

Finally, we arrive at **lactose**. Lactose is the primary sugar found in milk. It is a disaccharide composed of one molecule of **$\beta$-D-galactose** and one molecule of **$\beta$-D-glucose**, connected by a $\beta$-1,4-glycosidic linkage.

When we subject lactose to hydrolysis, the water molecule perfectly cleaves that specific linkage, releasing exactly what we've been looking for:

$$ 	ext{Lactose} + H_2O \xrightarrow{H^+} 	ext{D-galactose} + 	ext{D-glucose} $$

**Compound A** is undeniably lactose! This is a classic example of why knowing the monosaccharide composition of common disaccharides is so crucial in biochemistry.

Animated Solution for Chemistry - Organic Chemistry: Compound A gives D-galactose and D-glucose on hydrolysis. The compound A is

Select Answer:

Visualized Solution

Concept of Hydrolysis

Hydrolysis of Amylose

Hydrolysis of Sucrose

Hydrolysis of Maltose

Hydrolysis of Lactose

Final Conclusion

The Sigma Insight: Biomolecules

Analyzing the Setup

Investigating the Suspects

The Final Reveal

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