Question

What are histones? What are their functions?

Answer 1

Hint: These are made up of positively charged amino acid residues. They are nuclear proteins. They package DNA. They aid in ribosomal access to the DNA. They also aid in chromatin compaction along with nucleosome dynamics and transcription. They form nucleosomes. These nucleosomes form a solenoid by getting wrapped together in a spiral structure. They can be located inside the nucleus of the cell (eukaryotic organisms). They form nucleoproteins as they combine ionically with DNA.

Complete answer:
A histone is a protein which is highly alkaline and basic in nature. They are small and positively charged proteins. They could be termed as $$H1$$, $$H2A$$, $$H2B$$, $$H3$$, and $$H4$$. Two copies of each of these forms an octamer (histone octamer). They are composed of lysine and arginine. DNA is negatively charged, due to the phosphate groups in its phosphate-sugar backbone, so histones bind with DNA very tightly. Histones bind with DNA very tightly as the phosphate groups of DNA in its sugar-phosphate backbone is negatively charged.
The functions of histones are countless. These are found in eukaryotic cells and provide structural support to a chromosome. DNA wraps around complexes of histone proteins to fit into the nucleus. Thus, they confer a more compact shape to the chromosome. They also aid in regulation of gene expression and are critical in the packing of DNA into the cell and further into chromatin and chromosomes.

Note:
Changes in histone units may lead to changes in the physical state and function of the chromatin. This occurs during cell division and the transcription. Histones are water-soluble as discovered in avian red blood cell nuclei by Albrecht Kossel. Thymus and pancreas are said to have an abundance of histones. Bacteria lack histones but most archaea (prokaryotic) have them. Artificially incorporating histones in bacteria as studied in E.coli doesn’t shut down the gene expression.