# DBT JRF 2020 — Question 23

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

## Question

Which histone is NOT a part of the nucleosomes?

## Options

- **A.** H1
- **B.** H3
- **C.** H2B
- **D.** H2A

## Answer

Option A

## Explanation

Anaerobic digestion proceeds through four stages: (1) Hydrolysis — complex polymers (cellulose, proteins, lipids) broken to monomers by extracellular enzymes; (2) Acidogenesis — monomers fermented to volatile fatty acids (VFAs), alcohols, $\text{CO}_2$ , $\text{H}_2$ ; (3) Acetogenesis — VFAs converted to acetate, $\text{CO}_2$ , and $\text{H}_2$ ; (4) Methanogenesis — methanogens (archaea: Methanobacterium, Methanosarcina) convert acetate → $\text{CH}_4 + \text{CO}_2$ (acetoclastic pathway: $\text{CH}_3\text{COO}^- + \text{H}_2\text{O} \rightarrow \text{CH}_4 + \text{HCO}_3^-$ ) or $\text{CO}_2 + \text{H}_2 \rightarrow \text{CH}_4$ (hydrogenotrophic). Final biogas: ~60–70\% $\text{CH}_4$ , ~30–40\% $\text{CO}_2$ , traces of $\text{H}_2\text{S}$ .

Source: https://mypyqbuddy.com/questions/which-histone-is-not-a-part-of-the-6a05a8a02adafec47029322f