a1.2.13 - nucleosome structure

Question 1

describe the structure of eukaryotic DNA and associated histone proteins during interphase (chromatin).

Answer 1

to compact DNA while regulating gene accessibility for transcription, eukaryotic organisms organize their genomes:

1. DNA double helix.
2. DNA wraps around histone proteins, forming nucleosomes and the “beads on a string” structure.
3. multiple nucleosomes wrap into a fibre (chromatin).
4. supercoiling of the chromatin produces the chromosome (during mitosis and meiosis). supercoiling refers to the repeated twisting and winding of the DNA strand. supercoiling functions to reduce the space required for DNA packaging, allowing for more compact storage of DNA.

Question 2

draw and label the structure of a nucleosome, including the H1 protein, the octamer core proteins, linker DNA and two wraps of DNA.

Answer 2

the nucleosome is the basic unit of DNA packaging in eukaryotes. each nucleosome is composed of two turns of DNA wrapped around a group of eight histone proteins (called an octamer core). each nucleosome connects to the adjacent nucleosomes through another type of histone protein (called the H1) and a region of “linker” DNA.