Question

Alpha-helix is found in which level of protein structure ?

• A. Tertiary structure
• B. Quaternary structure
• C. Secondary structure
• D. Primary structure

Hint:

Think of protein levels like a phone cord: The wire is Primary, the coiling of the wire is Secondary, the tangled mess of the cord is Tertiary, and multiple cords together is Quaternary.

Answer 1

The Correct Option is C

Step 1: Understanding the Question
The question asks to identify the specific organizational level of a protein where the alpha-helix motif is formed. Proteins have four hierarchical levels of structure: primary, secondary, tertiary, and quaternary, each defined by the types of bonds and the complexity of the folding. Step 2: Key Formula or Approach
To solve this, we define each level of protein structure: - Primary: Order of amino acids. - Secondary: Localized folding (helices/sheets). - Tertiary: Total 3D folding of one chain. - Quaternary: Assembly of multiple chains. Step 3: Detailed Explanation
Primary Structure: This is simply the linear sequence of amino acids in a polypeptide chain, held together by covalent peptide bonds.
Secondary Structure: This level describes the local coiling or folding of the polypeptide backbone. It is stabilized by hydrogen bonds between the carbonyl oxygen and amide hydrogen of the peptide backbone. The two major types are the alpha-helix and the beta-pleated sheet.
Tertiary Structure: This is the overall three-dimensional shape of a single protein molecule. It results from interactions between the R-groups (side chains), such as disulfide bridges and hydrophobic interactions.
Quaternary Structure: This level exists only in proteins composed of more than one polypeptide subunit (e.g., hemoglobin).
Step 4: Final Answer
The alpha-helix is a fundamental component of the secondary structure of a protein. Thus, (A) is the correct answer.