Identify the monosaccharide containing only one asymmetric carbon atom in its molecule.

Options

A. Ribulose
B. Ribose
C. Erythrose
D. Glyceraldehyde

Answer

To identify the monosaccharide containing only one asymmetric carbon atom in its molecule, we will analyze the structures of the given options step by step.

### Step-by-Step Solution:

1. **Understanding Asymmetric Carbon:**
- An asymmetric carbon atom (also known as a chiral carbon) is a carbon atom that is bonded to four different substituents. This gives rise to optical activity in the compound.

2. **Analyzing Option 1: Ribulose**
- Ribulose is a five-carbon monosaccharide with a ketone functional group.
- Structure of Ribulose:
- CH2OH - C(=O) - CH - OH - CH - OH - CH2OH
- In this structure, none of the carbon atoms are attached to four different groups. Therefore, Ribulose does not contain an asymmetric carbon.

**Hint:** Check if any carbon in the structure has four different groups attached.

3. **Analyzing Option 2: Ribose**
- Ribose is also a five-carbon sugar and is a component of RNA.
- Structure of Ribose:
- CH2OH - CH - OH - CH - OH - CH - OH - CH=O
- Similar to Ribulose, none of the carbon atoms in Ribose are attached to four different groups. Thus, Ribose does not have an asymmetric carbon.

**Hint:** Look for carbon atoms that can be bonded to four distinct groups.

4. **Analyzing Option 3: Erythrose**
- Erythrose is a four-carbon sugar (aldose).
- Structure of Erythrose:
- CH2OH - CH - OH - CH - OH - CH=O
- In this structure, again, none of the carbon atoms are attached to four different groups. Therefore, Erythrose does not contain an asymmetric carbon.

**Hint:** Count the number of different groups attached to each carbon atom.

5. **Analyzing Option 4: Glyceraldehyde**
- Glyceraldehyde is a three-carbon sugar (triose) with an aldehyde group.
- Structure of Glyceraldehyde:
- CH2OH - CH - OH - CH=O
- In this case, the second carbon (C2) is attached to four different groups:
- CH2OH (from C1),
- H (hydrogen),
- OH (hydroxyl group),
- CHO (part of the aldehyde).
- Therefore, Glyceraldehyde contains one asymmetric carbon atom.

**Hint:** Identify the carbon atom that has four distinct substituents.

### Conclusion:
The monosaccharide containing only one asymmetric carbon atom in its molecule is **Glyceraldehyde**.