# DBT JRF 2020 — Question 24

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

## Question

If four atoms A, B, C and D are connected linearly and there is rotation possible along bond BC, dihedral angle on this bond is described as

## Options

- **A.** the angle formed between plane ABC and plane BCD
- **B.** the angle formed between plane ABD and plane ACD
- **C.** the angle between AC and BD
- **D.** the angle between AB and CD

## Answer

Option B

## Explanation

Nucleosome core particle composition: DNA (147 bp of DNA wrapped ~1.65 turns) + an octamer of 4 core histone pairs = $2\times(\text{H2A + H2B + H3 + H4})$ . H1 (linker histone) binds to the linker DNA connecting nucleosome core particles (the 'beads' between beads on a string) and to the entry/exit points of DNA around the core. H1 is NOT part of the core octamer. H1 compacts chromatin further by stabilising the 30 nm fibre. There are multiple H1 subtypes (H1.1–H1.5, H1°, H1t). H1 can be removed from chromatin without disrupting the core particle, confirming it is peripheral not core.

Source: https://mypyqbuddy.com/questions/if-four-atoms-a-b-c-and-d-6a05a8a02adafec470293230