# DBT JRF 2020 — Question 51

Exam: DBT JRF 2020 · Section: B · Topic: Environmental Science · Difficulty: Easy

## Question

To maintain soil fertility, the most sustainable agricultural practice is

## Options

- **A.** repeated use of fertilizers
- **B.** growing same crop
- **C.** burning the crop waste in the field
- **D.** crop rotation

## Answer

Option D

## Explanation

$\text{PrP}^C$ (normal cellular prion protein) is predominantly $\alpha$ -helix-rich (~42% $\alpha$ -helix, ~3% $\beta$ -sheet) and is GPI-anchored to the cell surface of neurons. $\text{PrP}^{Sc}$ (scrapie prion protein) is the misfolded, disease-causing isoform: predominantly $\beta$ -sheet-rich (~43% $\beta$ -sheet, ~30% $\alpha$ -helix), highly insoluble, forms aggregated amyloid fibrils, and is resistant to protease K digestion. $\text{PrP}^{Sc}$ acts as a template, inducing conformational conversion of $\text{PrP}^C \rightarrow \text{PrP}^{Sc}$ in a self-perpetuating ('protein-only hypothesis', Nobel Prize Prusiner 1997) manner. Accumulation of $\text{PrP}^{Sc}$ in neurons causes spongiform neurodegeneration (Creutzfeldt-Jakob disease, kuru, BSE, scrapie).

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