# DBT JRF 2020 — Question 39

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

## Question

Which of the following microorganism is used for commercial production of dextran?

## Options

- **A.** Streptomyces olivaceus
- **B.** Bacillus thuringiensis
- **C.** Leuconostoc mesenteroides
- **D.** Bacillus polymyxa

## Answer

Option C

## Explanation

Cellulose is the most abundant organic polymer on Earth and the main structural component of plant cell walls. It is a linear, unbranched homopolysaccharide of $\beta$ -D-glucose units linked by $\beta$ -1,4-glycosidic bonds ( $\beta$ configuration at C1 of glucose). The $\beta$ -1,4 linkages force each successive glucose to flip 180°, creating flat, extended chains that hydrogen-bond to adjacent chains, forming highly crystalline, rigid microfibrils. Contrast with starch: $\alpha$ -1,4 linkages (amylose) or $\alpha$ -1,4 and $\alpha$ -1,6 (amylopectin) create helical chains. Chitin is $\beta$ -1,4-linked N-acetylglucosamine. Callose is $\beta$ -1,3-linked glucose.

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