An `alpha`- helix is the example of which type of protein structure ?

Options

A. a) Primary
B. b) Secondary
C. c) Tertiary
D. d) Quaternary

Answer

To determine the type of protein structure represented by an alpha-helix, we can follow these steps:

### Step 1: Understand Protein Structure Levels
Proteins have four levels of structure: primary, secondary, tertiary, and quaternary. Each level of structure is defined by the arrangement of amino acids and the interactions between them.

### Step 2: Define Primary Structure
The primary structure of a protein refers to the linear sequence of amino acids in a polypeptide chain. This structure does not include any coiling or folding.

### Step 3: Define Secondary Structure
The secondary structure of a protein refers to the local folded structures that form within a polypeptide due to hydrogen bonding between the backbone atoms. The two main types of secondary structures are the alpha-helix and the beta-pleated sheet.

### Step 4: Identify the Alpha-Helix
The alpha-helix is a specific type of secondary structure characterized by a right-handed coil. It is stabilized by hydrogen bonds between the carbonyl oxygen of one amino acid and the amino hydrogen of another amino acid that is four residues earlier in the sequence.

### Step 5: Define Tertiary and Quaternary Structures
The tertiary structure refers to the overall three-dimensional shape of a single polypeptide chain, which is formed by the folding of the secondary structures. The quaternary structure involves the assembly of multiple polypeptide chains into a larger complex.

### Conclusion
Since the alpha-helix is a type of structure formed by the folding of the polypeptide chain and is stabilized by hydrogen bonds, it is classified as a **secondary structure** of proteins.

### Final Answer
The alpha-helix is an example of **secondary protein structure**.

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