Section 3: Genetics, Cellular and Molecular Biology
Recombinant DNA technology
Subtopic: Fundamentals of Recombinant DNA technology
Question Statement:
to 0.14
526.01 to 529.99
1 to 1
864 to 864
1196 to 1196
O to 0
2 to 2
2
52
3
NAT
2.20 to 2.30
25 to 25
153
3
NAT
48.50 to 49.50 OR
18521.20 to 18521.30
54
NAT
83.30 to 83.40
55
NAT
-219.30 to -219.20
Copyright : GATE 2020, IIT Delhi
Options:
(A) Vir genes are located within the T-DNA segment
(B) Phytohormone biosynthesis genes are located outside the T-DNA segment
(C) Opine catabolism genes are located within the T-DNA segment
(D) Opine biosynthesis genes are located within the T-DNA segment
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2020 Q.21)**
**1. Governing Concept**:
- **Topic**: Plant Biotechnology & Agrobacterium Ti Plasmid Architecture
- The tumor-inducing (Ti) plasmid of *Agrobacterium tumefaciens* contains two functional regions:
1. **T-DNA segment**: Flanked by 25-bp direct border repeats (Left and Right borders), transferred into the plant cell nucleus and integrated into chromatin. The T-DNA encodes **auxin and cytokinin biosynthesis genes** (causing crown gall tumor) and **opine biosynthesis genes** (providing nutrients for the bacterium).
2. **Non-transferred Ti plasmid backbone**: Encodes **Virulence (*vir*) genes** (mediating T-DNA excision and transfer), **Opine catabolism genes** (allowing *Agrobacterium* to catabolize opines), and replication origin (*ori*).
- Therefore, **opine biosynthesis genes are located within the T-DNA segment**.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: *Vir* genes are located outside the T-DNA on the Ti plasmid backbone.
- **Option (B) is INCORRECT**: Phytohormone biosynthesis genes (*iaaM, iaaH, ipt*) are located inside the T-DNA segment.
- **Option (C) is INCORRECT**: Opine catabolism genes reside on the plasmid backbone outside the T-DNA.
- **Option (D) [Opine biosynthesis genes are located within the T-DNA segment] is CORRECT**: Synthesized in plant cells using T-DNA-encoded enzymes.
**3. Final Answer**:
- **Correct Choice**: **D**
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