# DBT JRF 2020 — Question 35

Exam: DBT JRF 2020 · Section: B · Topic: Immunology · Difficulty: Hard

## Question

The enzyme-linked immunospot (ELISPOT) assay is highly sensitive because it can measure

## Options

- **A.** RNA copy number of the secreted cytokine
- **B.** total concentration of secreted cytokine
- **C.** size of the cytokine secreting cells
- **D.** frequency of cytokine secreting cells at the single cell level

## Answer

Option D

## Explanation

Eremothecium ashbyi (= Ashbya gossypii), an ascomycete fungus, naturally overproduces riboflavin (Vitamin B2) by >1000-fold above its metabolic needs. The biosynthetic pathway produces GTP → 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione → riboflavin via 6,7-dimethyl-8-ribityllumazine. Industrial riboflavin fermentation (>50,000 tonnes/year) uses Ashbya gossypii or recombinant Bacillus subtilis. Riboflavin (B2) is the precursor to FMN (flavin mononucleotide) and FAD (flavin adenine dinucleotide), essential coenzymes in oxidative metabolism. Saccharomyces rouxii is used for soy sauce; S. cerevisiae for bread/beer/bioethanol; Candida utilis for SCP (single cell protein).

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