Question

Demonstrate how the genome is compacted in eukaryote cells.

Answer 1

A brief explanation of every step involved in the compaction of DNA is listed below.

1. DNA has different levels of organization, from the basic unwound double helical chain to the chromosome, which is the final level of genome compaction.
2. Genome compaction is necessary due to the sheer length of DNA (2 meters) it has to be compacted to be around a few micrometres.
3. Moreover, there is the question of euchromatin and heterochromatin, euchromatin is relatively loosely packed. This loose organization makes it more transcriptionally active. This is another function of the condensation, only free DNA is able to make mRNA and by extension, proteins.
4. The first level of DNA organization is the nucleosome.
5. Round yo-yo like proteins around which DNA is wound like a spool tightly.
6. The nucleosome is a complex consisting of DNA, core histones, and linker proteins.
7. The histone proteins consisting of H3, H4, H2A, and H2B make up the core around wHich DNA winds.
8. Then come the linker histones which bind to the area of linker DNA between two nucleosomes.
9. The first step of compaction is when DNA is deposited onto the H3-H4 complex. This is called a sub nucleosome.
10. Then H2A -h2B dimers bind to the sub nucleosome.
11. Linkers are then bound to the linker DNA and the steps repeat for the next stretch of DNA, this is basic nucleosome assembly.
12. Each nucleosome is present after a certain distance forming the nucleofilament.
13. Next is the chromatin assembly.
14. The histones are acetylated, this allows proteins like the chromatin assembly factor to interact with H3-H4 during assembly.
15. Major multimeric protein complexes such as the chromatin remodeling machines then assemble the nucleosomes in bands.
16. The G, C, and R bands are known. They exist as part of the chromosome.