Question

The polypeptide chain in a protein has amino acids linked with each other in a specific sequence. This specific sequence of amino acids is called :

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

Hint:

Protein Structure Levels: Primary Structure \(\rightarrow\) Sequence of amino acids Secondary Structure \(\rightarrow\) \(\alpha\)-Helix and \(\beta\)-Sheet Tertiary Structure \(\rightarrow\) Three-dimensional folding of one chain Quaternary Structure \(\rightarrow\) Arrangement of multiple polypeptide chains

Answer 1

The Correct Option is A

Concept: Proteins are biological macromolecules formed by the polymerization of amino acids through peptide bonds. The properties and functions of proteins depend not only on the amino acids present but also on the precise order in which these amino acids are arranged. Protein structures are generally classified into four levels:

• Primary structure

• Secondary structure

• Tertiary structure

• Quaternary structure
Each level represents a different degree of structural organization.

Step 1: Understanding the primary structure of a protein. The primary structure of a protein refers to the exact sequence in which amino acids are arranged along the polypeptide chain. For example, if a protein chain contains amino acids arranged as \[ Ala-Gly-Val-Leu-Ser \] then this order itself represents the primary structure. Thus, the primary structure is simply the linear arrangement of amino acids connected through peptide bonds.

Step 2: Understanding the secondary structure of a protein. The secondary structure refers to regular folding patterns within the polypeptide chain. Common examples are \[ \alpha\text{-helix} \] and \[ \beta\text{-pleated sheet} \] These structures arise because of hydrogen bonding between different parts of the chain. Therefore, secondary structure is related to folding and not to the sequence itself. Hence, Option (B) is incorrect.

Step 3: Understanding the tertiary structure of a protein. The tertiary structure represents the three-dimensional arrangement of an entire polypeptide chain. It results from interactions such as

• Hydrogen bonding

• Ionic interactions

• Hydrophobic interactions

• Disulfide linkages
Since it describes the overall shape of a protein molecule, it is not the sequence of amino acids. Therefore, Option (C) is incorrect.

Step 4: Understanding the quaternary structure of a protein. The quaternary structure is observed when two or more polypeptide chains associate together to form a functional protein. For example, haemoglobin consists of multiple polypeptide subunits. Hence, quaternary structure refers to the arrangement of different subunits and not to the amino acid sequence. Therefore, Option (D) is incorrect.

Step 5: Identifying the structure described in the question. The question specifically mentions: quote "The polypeptide chain in a protein has amino acids linked with each other in a specific sequence." quote The term "specific sequence of amino acids" directly corresponds to the primary structure of a protein. Hence, \[ \boxed{\text{Primary Structure}} \] is the correct answer. Therefore, \[ \boxed{\text{Option (A)}} \]