Define the term “histone.” Which amino acids typically comprise a large part of histones? What about these amino acids make them ideal for interacting with DNA
Added by David H.
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” Histones are a group of small, positively charged proteins that play a crucial role in the packaging and organization of DNA within the cell nucleus. They help form nucleosomes, which are the fundamental units of chromatin, allowing DNA to be compacted and Show more…
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Histones are proteins that bind to DNA in eukaryotes, promoting the folding of DNA into tightly packed chromatin (this in turn can have important consequences for expression of genes). The sugar-phosphate backbone is negatively charged due to Oxygen atoms (of the phosphate groups within a phosphodiester bond). The pI of histones is very high (~11). A) What amino acid residues do you think are particularly enriched in histones, which specifically are contributing to such a high pI? B) How would these same amino acid residues (that are contributing to a high pI) contribute to strong binding of histone proteins to DNA?
Adi S.
The four core histones are relatively small proteins with a very high proportion of positively charged amino acids; the positive charge helps the histones bind tightly to DNA, regardless of its nucleotide sequence.
Histone proteins are positioned on DNA, in part, based on the abundance of clusters of A=T base pairs in DNA. Partial enzymatic digestion of chromatin results in DNA fragments of about 1.00 x 10^2 bp. Most histones are large (more than 250 amino acid residues), acidic proteins rich in Lys and Arg. The histones H2A, H2B, H3, and H4 make up the nucleosome octamer that binds DNA. DNA binding to histones enables overall positive supercoiling without enzymes that underwind the DNA helix. Degradation of linker DNA yields DNA fragments of about 200 bp.
Sri K.
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