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 is the most suitable type of impeller for mixing high viscosity
(viscosity > 105 cP) fluids?
(A) Propeller (B) Helical ribbon (C) Paddle (D) Flat blade turbine
Options:
(A) Propeller
(B) Helical ribbon
(C) Paddle
(D) Flat blade turbine
Official Answer Key:
B
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2016 Q.21)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Immunology (Generation of Antibody Diversity & V(D)J Recombination)
**2. Detailed Step-by-Step Analysis**:
- Primary antibody diversity is generated through combinatorial and junctional mechanisms:
1. **Combinatorial V(D)J joining**: Random pairing of distinct V, D, and J gene segments.
2. **Junctional diversity**: Generates massive variability precisely at the V-D and D-J junctions encoding the hypervariable CDR3 loop:
- **P-nucleotide addition**: Asymmetric cleavage of hairpin DNA loops by the RAG1/2 and Artemis complex produces palindromic (P) single-stranded overhangs.
- **Exonuclease nibbling**: Random removal of germline nucleotides by exonucleases.
- **N-nucleotide addition**: Non-templated (N) random nucleotides added to free 3′ ends by the enzyme **Terminal Deoxynucleotidyl Transferase (TdT)** before ligation.
- Thus, junctional diversity specifically results from the addition of **N and P nucleotides** (and exonuclease trimming) at segment boundaries.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Switch region recombination mediates immunoglobulin heavy chain class switching (isotype switching), not junctional diversity.
- **Option (B) [CORRECT]**: Junctional diversity results directly from the addition of N- and P-nucleotides during V(D)J recombination.
- **Option (C) [INCORRECT]**: The joining of segments per se is combinatorial diversity.
- **Option (D) [INCORRECT]**: Somatic hypermutation introduces point mutations in mature B cells during affinity maturation.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **B**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
Practice This in Real CBT Exam Interface
Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.