All monosaccharides containing five or six carbon atoms have

Options

A. Open chain structures only
B. Pyranose structures only
C. Furanose structures only
D. may have pyranose or furanose structures

Answer

To solve the question "All monosaccharides containing five or six carbon atoms have," we need to analyze the structures of monosaccharides and their forms.

### Step-by-Step Solution:

1. **Identify Monosaccharides**:
- Monosaccharides are the simplest form of carbohydrates and consist of single sugar units. Common examples include glucose (6 carbons) and ribose (5 carbons).

2. **Understand Carbon Count**:
- We are focusing on monosaccharides that contain either 5 or 6 carbon atoms. For instance, glucose (C6H12O6) has 6 carbon atoms, while ribose (C5H10O5) has 5 carbon atoms.

3. **Open Chain Structure**:
- Monosaccharides can exist in an open-chain (linear) form. For example, glucose can be represented in a straight chain where each carbon is connected to hydroxyl (OH) groups and hydrogen (H) atoms.

4. **Cyclic Forms**:
- In addition to the open-chain structure, monosaccharides can also form cyclic structures. For 6-carbon sugars like glucose, the cyclic form is called pyranose (6-membered ring). For 5-carbon sugars like ribose, the cyclic form is called furanose (5-membered ring).

5. **Equilibrium Between Forms**:
- Both the open-chain and cyclic forms exist in equilibrium. This means that monosaccharides can interconvert between their linear and cyclic forms.

6. **Conclusion**:
- Therefore, monosaccharides containing five or six carbon atoms can exist in an open-chain structure, a pyranose structure, a furanose structure, or can be in equilibrium between the open-chain and cyclic forms (pyranose and furanose).

7. **Final Answer**:
- The correct answer is that they may have pyranose or furanose structures, as well as open-chain forms.