Final answer:
In summary, nucleosomes, which are part of eukaryotic chromosomes, include a core of eight histone proteins with DNA wrapped around it about twice, greatly compacting DNA's length. These histones are rich in basic amino acids, aiding tight DNA binding and further compaction.
Step-by-step explanation:
A. Nucleosomes are present in eukaryotic chromosomes, but not in prokaryotic chromosomes. B. A nucleosome contains two molecules each of histones H2A and H2B as well as histones H3 and H4. C. A nucleosome core particle contains a core of histone with DNA wrapped around it approximately twice. D. Nucleosomes are aided in their formation by the high proportion of basic amino acids in histone proteins. E. Nucleosome formation compacts the DNA into approximately one-third of its original length.
Step-by-step explanation:
- Nucleosomes are structural units within the eukaryotic chromosome where DNA is wrapped around a set of histone proteins. Prokaryotes lack nucleosomes because they have a less complex packaging system for DNA and generally have circular chromosomes.
- The core particle of a nucleosome consists of eight histone proteins, with two copies each of H2A, H2B, H3, and H4. The histone H1 is involved in linking these nucleosomes together.
- DNA wraps around the histone core about 1.65 times in a nucleosome core particle, leading to a compact structure that reduces the length of DNA. Subsequent levels of compaction further reduce the length.
- Basic amino acids, which are prevalent in histones, positively charge these proteins, facilitating the tight binding with negatively charged DNA.
- The initial wrapping of DNA around nucleosomes condenses the length considerably, and further packing into higher order structures reduces the length even more, which is vital for fitting the long DNA molecules into the nucleus of eukaryotic cells.