Question

Which of the following can have a quaternary structure:

• A. Fatty acid
• B. Protein
• C. Polysaccharide
• D. RNA

Hint:

Only multi-subunit proteins (oligomeric proteins) possess quaternary structure.
Single-chain proteins, like myoglobin, only fold up to the tertiary level of structural organization.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Biochemical macromolecules exhibit different levels of structural organization to perform their biological functions.
Proteins are characterized by four levels of structure: primary, secondary, tertiary, and quaternary.

Step 2: Detailed Explanation:
- Primary structure: The linear sequence of amino acids in a polypeptide chain.
- Secondary structure: Local folding patterns, such as \( \alpha \)-helices and \( \beta \)-pleated sheets, stabilized by hydrogen bonds.
- Tertiary structure: The overall three-dimensional folding of a single polypeptide chain, stabilized by hydrophobic interactions, disulfide bonds, and ionic linkages.
- Quaternary structure: The spatial arrangement and assembly of multiple individual polypeptide chains (subunits) into a single functional multi-protein complex.
Examples of proteins with quaternary structure include hemoglobin (a tetramer of four subunits) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO).
Other macromolecules listed (fatty acids, polysaccharides, and RNA) do not exhibit this multi-subunit quaternary protein structure.
Therefore, quaternary structure is a defining level of organization in proteins.

Step 3: Final Answer:
Quaternary structure is a characteristic level of structural organization found in Proteins.