The back bone for different segments in a protein is in the following form.

Options

A. `alpha` - helix
B. `alpha`- pleated
C. coil
D. 1 or 3

Answer

To solve the question regarding the backbone for different segments in a protein, we will analyze the options provided and identify the correct structures that form the backbone of proteins.

### Step-by-Step Solution:

1. **Understanding Protein Structure**:
- Proteins are made up of amino acids linked together by peptide bonds, forming a polypeptide chain. The structure of proteins can be categorized into four levels: primary, secondary, tertiary, and quaternary.

2. **Identifying Secondary Structures**:
- The secondary structure of proteins refers to the local folded structures that form within a polypeptide due to hydrogen bonding between the backbone atoms. The most common types of secondary structures are:
- Alpha helix
- Beta pleated sheet
- Random coil

3. **Evaluating the Options**:
- **Alpha Helix**: This is a common secondary structure where the polypeptide chain coils into a helical shape, stabilized by hydrogen bonds.
- **Beta Pleated Sheet**: This structure consists of beta strands connected laterally by at least two or three hydrogen bonds, forming a sheet-like arrangement. However, the question specifies that this is not part of the backbone.
- **Coil**: This refers to irregular or non-repetitive structures in proteins, which can also be part of the backbone.
- **One-and-Three**: This option is not a standard term used to describe protein structure.

4. **Conclusion**:
- Based on the analysis, the backbone for different segments in a protein is primarily in the form of **alpha helix** and **coil**. Therefore, the correct answer is that the backbone consists of alpha helix and coil.

### Final Answer:
The backbone for different segments in a protein is in the form of **alpha helix and coil**.

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