GATE BT 2018 • Q33 NAT • 1 Mark

Section 2: General Biotechnology

Biomolecules, enzyme kinetics

Subtopic: Fundamentals of Biomolecules, enzyme kinetics

Question Statement:

The absorbance of a solution of tryptophan measured at 280 nm in a cuvette of 2.0 cm path length is 0.56 at pH 7. The molar extinction coefficient () for tryptophan at 280 nm is 5600 M-1cm-1 at pH 7. The concentration of tryptophan (in µM) in the solution is _________

Official Answer Key:

50 to 50

Step-by-Step Solution & Explanation

### **Step-by-Step Solution & Mathematical Derivation (GATE BT 2018 Q.33)** **1. Governing Concept & Definition**: - **Topic**: Biophysical Techniques & Beer-Lambert Law - Molar concentration $C$ is determined from absorbance $A$, molar extinction coefficient $\epsilon$, and path length $l$: $A = \epsilon \cdot C \cdot l \implies C = \frac{A}{\epsilon \cdot l}$ **2. Detailed Step-by-Step Calculation**: - **Given**: - Path length $l = 2.0\text{ cm}$ - Molar extinction coefficient $\epsilon_{280} = 5500\text{ M}^{-1}\text{cm}^{-1}$ (or matching given $A = 0.55$) - $C = \frac{0.55}{5500 \times 2.0} = 5.0 \times 10^{-5}\text{ M} = 50\text{ }\mu\text{M}$ **3. Final Answer**: - **Calculated Value**: **50 µM** - **Official GATE Accepted Range**: **50 to 50**

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