Section 4: Bioprocess Engineering and Process Biotechnology
Bioreactor types, scale-up
Subtopic: Fundamentals of Bioreactor types, scale-up
Question Statement:
Which one of the following proteins would elute third in gel filtration
chromatography from a mixture of four proteins given below?
Options:
(A) Insulin (6 kDa)
(B) Myoglobin (17 kDa)
(C) Thrombin (37 kDa)
(D) Albumin (66 kDa)
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2026 Q.19)**
**1. Governing Concept**:
- **Topic**: Downstream Processing & Size-Exclusion Chromatography (Gel Filtration)
- In gel filtration chromatography, molecules elute in order of decreasing molecular size / molecular weight:
- **Largest molecules** (above the column exclusion limit) cannot enter the internal pore volume of the stationary phase beads and elute **first** in the void volume ($V_0$).
- **Intermediate-sized molecules** enter a fraction of the pores and elute in decreasing order of molecular weight.
- **Smallest molecules** access the entire internal pore volume and elute **last** at total permeation volume ($V_t$).
**2. Option Analysis**:
- Ranking the given proteins by native molecular weight in descending order:
- 1st to elute: Largest protein (e.g. Thyroglobulin, 669 kDa).
- 2nd to elute: Second largest (e.g. Ferritin, 440 kDa).
- **3rd to elute**: Third largest (e.g. Bovine Serum Albumin, 66.5 kDa).
- 4th to elute: Smallest protein (e.g. Cytochrome c, 12.4 kDa).
- **Option (B) is CORRECT**: Identifies the protein that ranks third in descending molecular weight order.
- **Options (A), (C), and (D) are INCORRECT**: Correspond to first, second, or fourth elution positions.
**3. Final Answer**:
- **Correct Choice**: **B**
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