Section 4: Bioprocess Engineering and Process Biotechnology
Mass transfer in bioprocesses (kLa)
Subtopic: Fundamentals of Mass transfer in bioprocesses (kLa)
Question Statement:
An octapeptide composed of these L-amino acids - Lys, Thr, Ser, Met,
Arg, Trp, Tyr, Glu - was subjected to analyses with the following outcomes:
P. The N-terminal sequencing analysis by Sanger's method yielded
'Ser' at the N-terminus
Q. Chymotrypsin treatment gave a pentapeptide, a 'Tyr' containing
dipeptide and a free 'Glu'
R. Cyanogen bromide treatment gave two tetrapeptides
S. Trypsin treatment gave two tripeptides and a dipeptide
Which one of the following is the correct octapeptide sequence?
Options:
(A) Ser-Tyr-Arg-Met-Lys-Thr-Trp-Glu
(B) Ser-Arg-Lys-Met-Tyr-Thr-Trp-Glu
(C) Ser-Met-Lys-Arg-Thr-Tyr-Trp-Glu
(D) Ser-Arg-Met-Lys-Trp-Thr-Tyr-Glu
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2025 Q.38)**
**1. Governing Concept**:
- **Topic**: Biochemistry & Glycolysis Regulation (Phosphofructokinase-1)
- **Phosphofructokinase-1 (PFK-1)** catalyzes the committed, rate-limiting step of glycolysis:
$\text{Fructose 6-phosphate} + \text{ATP} \rightarrow \text{Fructose 1,6-bisphosphate} + \text{ADP}$
- Allosteric regulation of PFK-1:
- **Allosteric Activators**: **Fructose 2,6-bisphosphate ($\text{F-2,6-BP}$)** (the most potent physiological activator), **AMP**, and **ADP**.
- **Allosteric Inhibitors**: **ATP** (high energy charge signals sufficient energy) and **Citrate** (signals abundant TCA cycle precursors).
**2. Option Analysis**:
- **Option (A) is INCORRECT**: High ATP allosterically inhibits PFK-1 by binding to a low-affinity regulatory site.
- **Option (B) is INCORRECT**: Citrate is an allosteric inhibitor, not an activator.
- **Option (C) is CORRECT**: Fructose 2,6-bisphosphate is the most potent allosteric activator, relieving ATP inhibition and increasing affinity for fructose 6-phosphate.
- **Option (D) is INCORRECT**: AMP stimulates PFK-1, it does not inhibit.
**3. Final Answer**:
- **Correct Choice**: **C**
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