Section 4: Bioprocess Engineering and Process Biotechnology
Mass transfer in bioprocesses (kLa)
Subtopic: Fundamentals of Mass transfer in bioprocesses (kLa)
Question Statement:
Which of the following technique(s) can be used to study conformational changes in
myoglobin?
P. Mass spectrometry
Q. Fluorescence spectroscopy
R. Circular dichroism spectroscopy
S. Light microscopy
Options:
(A) P only
(B) P and S only
(C) Q and R only
(D) S only
Official Answer Key:
C
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2018 Q.22)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Biophysical Techniques (Protein Structure & Spectroscopy)
**2. Detailed Step-by-Step Analysis**:
- Conformational changes in globins (like myoglobin upon ligand binding, e.g., deoxymyoglobin $\leftrightarrow$ oxymyoglobin) involve alterations in secondary structure, tertiary packing, and electronic environment around the heme prosthetic group:
- **P. Circular Dichroism (CD)**: Far-UV CD (190–250 nm) sensitively measures secondary structure content ($lpha$-helices, $eta$-sheets), while near-UV CD (250–320 nm) reports on the tertiary asymmetric environment of aromatic residues and prosthetic groups. Both directly detect conformational transitions in myoglobin.
- **Q. Fluorescence spectroscopy**: The intrinsic fluorescence of tryptophan residues (such as Trp14 and Trp7) in myoglobin is highly sensitive to local dielectric environments and distance-dependent quenching by the heme iron, making it an excellent probe for conformational changes.
- **R. Optical rotatory dispersion (ORD)**: Measures optical rotation as a function of wavelength and directly probes chiral secondary structures ($lpha$-helical content) and conformational shifts.
- **S. Infrared (FTIR) spectroscopy**: Amide I ($1600-1700 ext{ cm}^{-1}$, $C=O$ stretch) and Amide II bands directly monitor secondary structural changes and protein conformational dynamics.
- Therefore, all four techniques (P, Q, R, and S) can be employed to track conformational transitions in myoglobin.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Omits R and S.
- **Option (B) [INCORRECT]**: Omits fluorescence and infrared spectroscopy.
- **Option (C) [CORRECT]**: P, Q, R, and S can all be used to investigate protein conformational changes.
- **Option (D) [INCORRECT]**: Incomplete subset.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **C**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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