DNA packaging (detailed explanation)

How DNA is Packaged (Advanced). This video shows advanced explanation of dna packaging. The essential unit of DNA packaging is the nucleosome. A nucleosome consists of a small amount of DNA wrapped up with protein. The proteins that interact with DNA to form chromatin comprise a family of basic (positively charged) proteins called histones. There are five different types of histone protein: H1, H2A, H2B, H3, and H4. Of these, two molecules each of H2A, H2B, H3, and H4 combine to form a histone octamer. DNA wraps around the octamer, making 1 3/4 turns around the protein complex. The amount of DNA associated with the histone octamer is 146 bp. The octamer plus the DNA comprise what is called the nucleosome core. A small stretch of DNA (60 bp) runs between adjacent nucleosome cores, and is known as the linker. A single nucleosome consists of one core plus a linker. The total amount of DNA involved in a single nucleosome is approximately 206 bp. Chromatin therefore consists of DNA wrapped around one histone octamer after another, like a long string of beads (as shown in panel B). In fact, when viewed under an electron microscope, this configuration looks just like beads on a string. This configuration, known as the 10 nm chromatin fiber (based on its approximate diameter), corresponds to the state of chromosomes during interphase, when most of the chromosomes exist as euchromatin. Read more: http://www.emunix.emich.edu/~rwinning/genetics/chrom.htm

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Channels: Molecular Biology Molecular Genetics

Tags: DNA packaging

Uploaded by: ( Send Message ) on 23-11-2010.

Duration: 1m 43s