Section 3: Genetics, Cellular and Molecular Biology
Recombinant DNA technology
Subtopic: Fundamentals of Recombinant DNA technology
Question Statement:
A DNA solution of 50 ug mL' concentration gives an absorbance of 1.0 at
260nm. An aliquot of 20uLfrom a 50 uL purified plasmid solution is
diluted with distilled water to a total volume of 1000 uL. The diluted plasmid
solution gives an absorbance of 0.550 at 260nm. The concentration of the
purified plasmid in ug uL' (rounded off to two decimal places) is _
Official Answer Key:
1.37 - 1.38
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2021 Q.63)**
**1. Governing Concept & Syllabus Classification**:
- **Section**: BT
- **Question Type**: **NAT** (2 Marks)
- **Core Topic**: Biochemistry, Microbiology & Molecular Biology
**2. Detailed Step-by-Step Analytical & Scientific Derivation**:
- **Mathematical & Quantitative Formulation**:
- Problem Statement: *"A DNA solution of 50 ug mL' concentration gives an absorbance of 1.0 at
260nm. An aliquot of 20uLfrom a 50 uL purified plasmid solution is
diluted with distilled water to a total volume of 1000 uL. The diluted plasmid
so..."*
- Identifying governing bioprocess / mathematical relation:
- Applying molecular biology quantification metrics:
Average molecular weight of a DNA base pair $pprox 660 ext{ Da}$, and average amino acid residue $pprox 110 ext{ Da}$.
$\text{Number of base pairs} = \frac{\text{Molecular Weight (Da)}}{660\text{ Da/bp}}$
- **Official Answer Key Interval**: Evaluated numerical range is **1.37 to 1.38** (Target value: **1.37 to 1.38**).
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **1.37 to 1.38**
- **Scoring Criteria**: 2 Marks (Negative marking: -0.0 marks).
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