Which one of the following is a non-reducing carbohydrate?

Options

A. Maltose
B. Sucrose (table sugar)
C. Lactose
D. Ribose 5-phosphate

Answer

To determine which of the given options is a non-reducing carbohydrate, we can follow these steps:

### Step 1: Understand the Definition of Reducing and Non-Reducing Sugars
- Reducing sugars are carbohydrates that have a free aldehyde or ketone group, allowing them to reduce other compounds.
- Non-reducing sugars do not have a free aldehyde or ketone group, meaning they cannot act as reducing agents.

### Step 2: Analyze Each Option
1. **Maltose**:
- Maltose is a disaccharide formed from two glucose molecules linked by an alpha 1,4 glycosidic bond.
- The second glucose retains a free aldehyde group, making maltose a reducing sugar.

2. **Sucrose**:
- Sucrose is a disaccharide composed of one glucose and one fructose unit linked by an alpha 1, beta 2 glycosidic bond.
- The aldehyde group of glucose is involved in the bond with the ketone group of fructose, leaving no free aldehyde or ketone group. Thus, sucrose is a non-reducing sugar.

3. **Lactose**:
- Lactose is a disaccharide made up of glucose and galactose.
- It has a free aldehyde group on glucose, which means lactose is a reducing sugar.

4. **Ribose 5-phosphate**:
- Ribose 5-phosphate is a monosaccharide.
- All monosaccharides, including ribose, typically have a free aldehyde or ketone group, making them reducing sugars.

### Step 3: Conclusion
From the analysis, the only non-reducing carbohydrate among the options provided is **sucrose**.

### Final Answer
**Sucrose is a non-reducing carbohydrate.**

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