Section 4: Bioprocess Engineering and Process Biotechnology
Bioreactor types, scale-up
Subtopic: Fundamentals of Bioreactor types, scale-up
Question Statement:
The power required for agitation of non-aerated medium in fermentation is ________ kW.
Operating conditions are as follows:
Fermentor diameter = 3 m
Number of impellers = 1
Mixing speed = 300 rpm
Diameter of the Rushton turbine = 1 m
Viscosity of the broth = 0.001 Pa.s
Density of the broth = 1000 kg.m
-3
Power number = 5
Options:
(A) sucrose and maltose
(B) sucrose and isomaltose
(C) maltose and isomaltose
(D) lactose and cellobiose
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2016 Q.20)**
**1. Governing Concept & Question Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Topic**: Biochemistry / Carbohydrate Chemistry (Disaccharide Structures & Glycosidic Linkages)
**2. Detailed Step-by-Step Analysis**:
- Let us analyze the glycosidic bonds in common disaccharides:
- **Lactose**: Composed of $\beta$-D-galactopyranose and D-glucopyranose joined by a **$\beta(1 \to 4)$** glycosidic bond ($\text{Gal}\beta1\to4\text{Glc}$).
- **Cellobiose**: Composed of two D-glucopyranose units joined by a **$\beta(1 \to 4)$** glycosidic bond ($\text{Glc}\beta1\to4\text{Glc}$); the repeating disaccharide unit of cellulose.
- **Maltose**: Composed of two D-glucose units linked by an **$\alpha(1 \to 4)$** glycosidic bond.
- **Isomaltose**: Composed of two D-glucose units linked by an **$\alpha(1 \to 6)$** glycosidic bond.
- **Sucrose**: Composed of $\alpha$-D-glucose and $\beta$-D-fructose linked by an **$\alpha1 \leftrightarrow \beta2$** glycosidic bond.
- Therefore, the disaccharide pair that both contain **$\beta(1 \to 4)$** glycosidic linkages is **lactose and cellobiose**.
- **Option-by-Option Evaluation**:
- **Option (A) [INCORRECT]**: Sucrose has $\alpha1 \leftrightarrow \beta2$, and maltose has $\alpha(1 \to 4)$.
- **Option (B) [INCORRECT]**: Isomaltose has $\alpha(1 \to 6)$.
- **Option (C) [INCORRECT]**: Maltose is $\alpha(1 \to 4)$ and isomaltose is $\alpha(1 \to 6)$.
- **Option (D) [CORRECT]**: Both lactose and cellobiose contain $\beta(1 \to 4)$ glycosidic linkages.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **D**
- **Scoring Criteria**: +1.0 Mark (Negative marking: -0.33 marks).
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