Which is type of secondary protein structure

Options

A. `alpha`-helix
B. `beta`-pleated
C. Collagen helix
D. All the above.

Answer

To determine which types of structures are classified as secondary protein structures, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Protein Structure Levels**:
- Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. The primary structure is the sequence of amino acids, while the secondary structure involves the folding and coiling of this sequence.

**Hint**: Remember that the primary structure is just the sequence of amino acids.

2. **Identify Secondary Structures**:
- The secondary structure refers to specific shapes that the polypeptide chain can form, primarily due to hydrogen bonding. The most common types of secondary structures are:
- **Alpha Helix**: A coiled structure stabilized by hydrogen bonds between the carbonyl oxygen of one amino acid and the hydrogen of the amine group of another amino acid four residues down the chain.
- **Beta Pleated Sheet**: A sheet-like structure formed by hydrogen bonds between different segments of the polypeptide chain, which can be parallel or antiparallel.

**Hint**: Look for structures that involve hydrogen bonding between amino acids.

3. **Consider Other Structures**:
- **Collagen Helix**: This is another form of secondary structure. It is similar to the alpha helix but is more stretched and is left-handed. It is also stabilized by hydrogen bonds.

**Hint**: Collagen is a specific type of protein that has a unique helical structure.

4. **Evaluate the Options**:
- The question provides four options:
- Option 1: Alpha Helix
- Option 2: Beta Pleated Sheet
- Option 3: Collagen Helix
- Option 4: All of the above
- Since all three options (alpha helix, beta pleated sheet, and collagen helix) are indeed types of secondary protein structures, the correct answer is option 4.

**Hint**: If all listed options are valid types of a category, the answer is often "all of the above".

### Final Answer:
The correct answer is **Option 4: All of the above**. All listed structures are types of secondary protein structures.