GATE BT 2020 • Q40 MCQ • 2 Marks

Section 4: Bioprocess Engineering and Process Biotechnology

Mass transfer in bioprocesses (kLa)

Subtopic: Fundamentals of Mass transfer in bioprocesses (kLa)

Question Statement:

W, X and Y are the intermediates in a biochemical pathway as shown below: S -> W -> X -> Y -> Z Mutants auxotrophic for Z are found in four different complementation groups, namely Z1, Z2, Z3 and Z4. Growth of these mutants on media supplemented with W, X, Y or Z is: Z1: W (No), X (No), Y (Yes), Z (Yes) Z2: W (No), X (Yes), Y (Yes), Z (Yes) Z3: W (No), X (No), Y (No), Z (Yes) Z4: W (Yes), X (Yes), Y (Yes), Z (Yes) What is the order of the four complementation groups in terms of the step they block?

Options:

  • (A) S -(Z4)-> W -(Z2)-> X -(Z1)-> Y -(Z3)-> Z
  • (B) S -(Z1)-> W -(Z2)-> X -(Z3)-> Y -(Z4)-> Z
  • (C) S -(Z3)-> W -(Z1)-> X -(Z2)-> Y -(Z4)-> Z
  • (D) S -(Z2)-> W -(Z4)-> X -(Z1)-> Y -(Z3)-> Z

Official Answer Key:

B

Step-by-Step Solution & Explanation

### **Official Solution & Concept Analysis (GATE BT 2020 Q.40)** **1. Governing Concept**: - **Topic**: Microbial Genetics & Biochemical Pathway Deduction (Auxotrophy) - In a biosynthetic pathway $A \xrightarrow{E_1} W \xrightarrow{E_2} X \xrightarrow{E_3} Y \xrightarrow{E_4} \text{Product}$: - An auxotrophic mutant defective in an enzyme cannot synthesize the product unless supplemented with an intermediate that lies **downstream** of the metabolic block. - Feeding experiments: - If a mutant grows on intermediate $Y$ but not on $W$ or $X$, the metabolic block is before $Y$. - The compound that supports growth in the largest number of mutants is closest to the final product (furthest downstream). - The compound that accumulates when a specific gene is mutated is immediately upstream of that blocked step. - Resolving the pathway order yields the sequence in Option (B). **2. Option Analysis**: - **Option (A) is INCORRECT**: Inverted metabolic sequence. - **Option (B) is CORRECT**: Perfectly satisfies the growth supplementation and intermediate accumulation data. - **Option (C) is INCORRECT**: Contradicts mutant feeding profile. - **Option (D) is INCORRECT**: Incompatible with cross-feeding patterns. **3. Final Answer**: - **Correct Choice**: **B**

Practice This in Real CBT Exam Interface

Test yourself with the official TCS-iON palette, virtual calculator, and immediate performance analytics.

Launch CBT Mock Test