# DBT JRF 2020 — Question 79

Exam: DBT JRF 2020 · Section: B · Topic: Biochemistry · Difficulty: Medium

## Question

A protein with 1000 amino acids was tagged with GFP. The molecular weight of GFP is 26 KDa. What will be the most likely molecular weight of the fused target protein?

## Options

- **A.** 100 KDa
- **B.** 136 KDa
- **C.** 126 KDa
- **D.** 150 KDa

## Answer

Option B

## Explanation

Average amino acid molecular weight $\approx 110$ Da (ranges from 75 Da for Gly to 186 Da for Trp; weighted average for a typical protein $\approx 110$ Da). For a GFP-tagged protein: Protein (1000 AA): $1000 \times 110 = 110{,}000 \text{ Da} = 110 \text{ kDa}$ . GFP tag: 26 kDa (239 amino acids). Total fusion protein: $110 + 26 = 136 \text{ kDa}$ . Note: for SDS-PAGE, the fusion protein would run as a single band at ~136 kDa. GFP does not significantly alter the migration pattern of large proteins but is easily detectable by fluorescence.

Source: https://mypyqbuddy.com/questions/a-protein-with-1000-amino-acids-was-tagged-6a05a8a02adafec470293267