nucleosomes

(noun)

The fundamental subunit of chromatin, composed of a little less than two turns of DNA wrapped around a set of eight proteins called histones.

Related Terms

Examples of nucleosomes in the following topics:

  • Epigenetic Control: Regulating Access to Genes within the Chromosome

    • These nucleosomes control the access of proteins to the underlying DNA.
    • Nucleosomes can slide along DNA.
    • When the nucleosomes are spaced far apart (bottom), the DNA is exposed.
    • Modifications to the histones and DNA affect nucleosome spacing.
    • Modifications affect nucleosome spacing and gene expression.

  • Eukaryotic Chromosomal Structure and Compaction

    • The beadlike, histone DNA complex is called a nucleosome.
    • DNA connecting the nucleosomes is called linker DNA.
    • The next level of compaction occurs as the nucleosomes and the linker DNA between them are coiled into a 30-nm chromatin fiber.
    • Double-stranded DNA wraps around histone proteins to form nucleosomes that have the appearance of "beads on a string."
    • The nucleosomes are coiled into a 30-nm chromatin fiber.

  • Elongation and Termination in Eukaryotes

    • These DNA–histone complexes, collectively called nucleosomes, are regularly spaced and include 146 nucleotides of DNA wound twice around the eight histones in a nucleosome like thread around a spool.
    • FACT reassembles the nucleosome behind the RNA Polymerase II by returning the missing histones to it.
    • DNA in eukaryotes is packaged in nucleosomes, which consist of an octomer of 4 different histone proteins.
    • When DNA is tightly wound twice around a nucleosome, RNA Polymerase II cannot access it for transcription.
    • FACT also reassembles the nucleosome immediately behindd the RNA Polymerase by returning the missing histones.

  • DNA Packaging

    • At the most basic level, DNA is wrapped around proteins known as histones to form structures called nucleosomes.
    • This nucleosome is linked to the next one with the help of a linker DNA.
    • The euchromatin usually contains genes that are transcribed, with DNA packaged around nucleosomes but not further compacted.

  • Prokaryotic versus Eukaryotic Gene Expression

    • Regulation may occur when the DNA is uncoiled and loosened from nucleosomes to bind transcription factors (epigenetics), when the RNA is transcribed (transcriptional level), when the RNA is processed and exported to the cytoplasm after it is transcribed (post-transcriptional level), when the RNA is translated into protein (translational level), or after the protein has been made (post-translational level).

  • Bacterial Chromosomes in the Nucleoid

    • In contrast to histones, the DNA-binding proteins of the nucleoid do not form nucleosomes, in which DNA is wrapped around a protein core.

  • Binary Fission

    • Although the DNA of the nucleoid is associated with proteins that aid in packaging the molecule into a compact size, there are no histone proteins and thus, no nucleosomes in prokaryotes.

  • DNA Replication in Eukaryotes

    • Eukaryotic DNA is bound to proteins known as histones to form structures called nucleosomes.
    • Instead, the replication initiation proteins might identify and bind to specific modifications to the nucleosomes in the origin region.

  • Cell Signaling and Gene Expression

    • Regulation may occur when the DNA is uncoiled and loosened from nucleosomes to bind transcription factors (epigenetic level); when the RNA is transcribed (transcriptional level); when the RNA is processed and exported to the cytoplasm after it is transcribed (post-transcriptional level); when the RNA is translated into protein (translational level); or after the protein has been made (post-translational level).

  • The Mitotic Phase and the G0 Phase

    • Nuclear envelopes form around the chromosomes and nucleosomes appear within the nuclear area.