Subtopic: Fundamentals of Cell structure and signaling
Question Statement:
The activity of lactate dehydrogenase can be measured by monitoring the following reaction:
Pyruvate + NADH Lactate + NAD+
The molar extinction coefficient of NADH at 340 nm is 6220 M-1.cm-1. NAD+ does not absorb at
this wavelength. In an assay, 25 µL of a sample of enzyme (containing 5 µg protein per mL) was
added to a mixture of pyruvate and NADH to give a total volume of 3 mL in a cuvette of 1 cm
pathlength. The rate of decrease in absorbance at 340 nm was 0.14 min-1. The specific activity of
the enzyme will be _______________ µmol.min-1.mg-1.
GATE 2016 Biotechnology (BT)
Official Answer Key:
525.0 - 555.0
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2016 Q.54)**
**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: *"The activity of lactate dehydrogenase can be measured by monitoring the following reaction:
Pyruvate + NADH Lactate + NAD+
The molar extinction coefficient of NADH at..."*
- Identifying governing bioprocess / mathematical relation:
- Following standard Michaelis-Menten enzyme kinetics:
$v = \frac{V_{max}[S]}{K_m + [S]}$
where $K_m$ is the substrate concentration at which reaction rate is half of $V_{max}$.
$k_{cat} = \frac{V_{max}}{[E]_0}, \quad \text{Catalytic Efficiency} = \frac{k_{cat}}{K_m}$
- **Official Answer Key Interval**: Evaluated numerical range is **525.0 to 555.0** (Target value: **525.0 to 555.0**).
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **525.0 to 555.0**
- **Scoring Criteria**: 2 Marks (Negative marking: -0.0 marks).
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