Section 3: Genetics, Cellular and Molecular Biology
Recombinant DNA technology
Subtopic: Fundamentals of Recombinant DNA technology
Question Statement:
Which one of the following hosts is used in mammalian cell culture
for the production of glycosylated recombinant therapeutic proteins?
Options:
(A) Pichia pastoris
(B) Sf9 cells
(C) Escherichia coli
(D) Chinese hamster ovary cells
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2025 Q.20)**
**1. Governing Concept**:
- **Topic**: Biophysics & Circular Dichroism (CD) Spectroscopy of Proteins
- Far-UV CD spectroscopy (190–250 nm) probes peptide backbone secondary structure:
- **$\alpha$-Helix**: Displays two prominent negative minima at **208 nm** ($\pi \to \pi^*$ parallel transition) and **222 nm** ($n \to \pi^*$ transition), and a strong positive peak at **192 nm**.
- **$\beta$-Sheet**: Displays a single negative minimum at **218 nm** and a positive maximum at **195 nm**.
- **Random Coil (Disordered)**: Displays a strong negative minimum near **198 nm** and weak band near zero above 210 nm.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Describes predominantly random coil / disordered conformation.
- **Option (B) is INCORRECT**: A single minimum at 218 nm is characteristic of $\beta$-sheet structure.
- **Option (C) is CORRECT**: Negative ellipticity minima at both 208 nm and 222 nm is the definitive diagnostic signature of an $\alpha$-helical polypeptide.
- **Option (D) is INCORRECT**: Tryptophan near-UV tertiary CD occurs between 250–320 nm, not far-UV backbone spectra.
**3. Final Answer**:
- **Correct Choice**: **C**
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