Final answer:
The statement mentioning tyrosine as a reason for histones' positive charge is false. Histones are positively charged due to the presence of lysine and arginine, which bind tightly to the negatively charged DNA. Histone modifications regulate DNA packaging and gene expression.
Step-by-step explanation:
The statement 'Histones contain a large number of tyrosine and series and are therefore positively charged proteins' is false. Histones are indeed positively charged, but not due to tyrosine. Histones are basic proteins that are rich in the amino acids lysine and arginine, which are responsible for their positive charge. These charged side chains are crucial for binding to the acidic, negatively charged phosphodiester backbone of DNA, facilitating the formation of nucleosomes. In eukaryotic cells, DNA wraps around octamers of histones, forming a nucleosome, which is the fundamental unit of DNA packaging.
Histones play a key role in regulating gene expression as their interaction with DNA can be modified by the addition of chemical groups such as phosphates, methyl groups, or acetyl groups to histone tails. These modifications can alter how tightly the DNA is wound around the histone proteins, which in turn affects the accessibility of transcription machinery to the DNA and regulates gene expression.