Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
Which of the following are CORRECT about protein structure?
P. Secondary structure is formed by a repeating pattern of interactions
among the polypeptide backbone atoms
Q. Tertiary structure is the three-dimensional arrangement of the
polypeptide backbone atoms only
R. Quaternary structure refers to an assembly of multiple polypeptide
subunits
Options:
(A) P and Q only
(B) P and R only
(C) Q and R only
(D) P, Q and R
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2022 Q.42)**
**1. Governing Concept**:
- **Topic**: Biochemistry & Hierarchy of Protein Architecture
- Evaluating structural levels of proteins:
- **P. Secondary structure**: Formed by regular, repeating hydrogen bonding patterns between polypeptide **backbone** amide ($\text{N}-\text{H}$) and carbonyl ($\text{C}=\text{O}$) atoms ($\alpha$-helices, $\beta$-sheets) $\rightarrow$ **CORRECT**.
- **Q. Tertiary structure**: The 3D arrangement of the polypeptide chain including both **backbone and side-chain atoms (R-groups)**, stabilized by hydrophobic interactions, salt bridges, hydrogen bonds, and disulfide bonds. Restricting it to "backbone atoms only" is factually false $\rightarrow$ **INCORRECT**.
- **R. Quaternary structure**: The spatial arrangement and assembly of multiple polypeptide chains (subunits) into an oligomeric functional complex $\rightarrow$ **CORRECT**.
- Therefore, statements **P and R only** are correct.
**2. Option Analysis**:
- **Option (A) [P and Q only] is INCORRECT**: Statement Q erroneously excludes amino acid side-chain interactions.
- **Option (B) [P and R only] is CORRECT**: P and R are precise, textbook structural definitions.
- **Option (C) [Q and R only] is INCORRECT**: Q is false.
- **Option (D) [P, Q and R] is INCORRECT**: Includes incorrect statement Q.
**3. Final Answer**:
- **Correct Choice**: **B**
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