Question
Write short note on : DNA packaging in eukaryotic cell.
✓
Answer
1. In eukaryotic cells, DNA ( $2.2$ metres) is condensed, coiled and supercoiled to be packaged efficiently in the nucleus ( $10^{-16} m$ ).
2. DNA is associated with histone and non-histone proteins.
3. Histones are a set of positively charged, basic proteins, rich in basic amino acid residues lysine and arginine.
4. Nucleosome consists of nucleosome core (two molecules of each of histone proteins viz. $H _2 A, H _2 B, H _3$ and $H _4$ forming histone octamer) and negatively charged DNA $( 146\ bps )$ that wraps around the histone octamer by $1 3/4$ turns.
5. $H _1$ protein binds the DNA thread where it enters and leaves the nucleosome.
6. Adjacent nucleosomes are linked with linker DNA (varies in length from 8 to $114\ bp$, average length of linker DNA is about 54 bp ).
7. Each nucleosome contains $200\ bp$ of DNA.
8. Packaging involves formation of - Beads on string ( $10\ nm$ diameter), Solenoid fibre (looks like coiled telephone wire, $30\ nm$ diameter/ $300 \AA$ ), Chromatin fibre and Chromosome.
9. Non-Histone Chromosomal Proteins (NHC) contribute to the packaging of chromatin at a higher level.
2. DNA is associated with histone and non-histone proteins.
3. Histones are a set of positively charged, basic proteins, rich in basic amino acid residues lysine and arginine.
4. Nucleosome consists of nucleosome core (two molecules of each of histone proteins viz. $H _2 A, H _2 B, H _3$ and $H _4$ forming histone octamer) and negatively charged DNA $( 146\ bps )$ that wraps around the histone octamer by $1 3/4$ turns.
5. $H _1$ protein binds the DNA thread where it enters and leaves the nucleosome.
6. Adjacent nucleosomes are linked with linker DNA (varies in length from 8 to $114\ bp$, average length of linker DNA is about 54 bp ).
7. Each nucleosome contains $200\ bp$ of DNA.
8. Packaging involves formation of - Beads on string ( $10\ nm$ diameter), Solenoid fibre (looks like coiled telephone wire, $30\ nm$ diameter/ $300 \AA$ ), Chromatin fibre and Chromosome.
9. Non-Histone Chromosomal Proteins (NHC) contribute to the packaging of chromatin at a higher level.
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