We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What are Histones?

By M.J. Casey
Updated May 21, 2024
Our promise to you
All The Science is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At All The Science, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

Histones are structures in eukaryotic cells and some single-celled microorganisms of the phylum Euryarchaeota that serve as spools around which the cell’s deoxyribonucleic acid (DNA) wraps very closely. Without the space conservation that histones enable, cells could not contain their own DNA. Histones also play important roles in gene expression by enabling or hindering the access of transcription-active molecules to the DNA genes. A third task is to maintain structural integrity of the DNA and of the much larger chromosome.

The substances that comprise histones are proteins that differ little from species to species. The most common proteins are called H1/H5, H2A, H2B, H3 and H4. The DNA is bound closely to the histones by the attraction between the side groups of the histone proteins and the DNA. This attractive force is modified by the addition of acetyl or methyl groups to a few lysine or arginine amino acids near the end of the H3 and H4 proteins. The tightening or loosening of the DNA strand results in the genes being accessible or inaccessible, known as turning the gene "on" or "off."

In most cells, regardless of source, eight histone proteins, consisting of two each of H2A, H2B, H3 and H4, form an octet structure. Approximately 146 base pairs of DNA wrap around the octet structure almost twice to form a "nucleosome." A short loop of DNA, stabilized by the H1 protein or its H5 analog, leads to the next nucleosome, forming a structure that is often characterized as "beads on a string." The nucleosomes and their linking DNA sections form tight spirals, with six nucleosomes per turn, to make what are called chromatin fibers. The fibers pack together to form a chromosome.

Histone proteins H2A, H2B, H3 and H4 are of relatively low molecular weight, consisting of 120 to 135 amino acids per protein molecule. Histones H1/H5 are much longer and give structural framework to the nucleosomes, much like a steel rod linking a series of disks. In human cells, if all the DNA were uncoiled and laid end to end, the strand would be about 70 inches long (1.8 m) yet only about 0.0000007 inches thick (180 nanometers). By coiling and recoiling the substructures, the 23 pairs of chromosomes function in a nucleus that is itself less than 0.0004 inches (10 micrometers) in diameter. Histones make this folding possible by controlling the molecular environment.

Histones were initially thought to have only the types mentioned above. Research, however, has pointed to much more diversity than was previously accepted. The basic molecules are still relatively the same even between organisms as divergent as yeast and mammals. This trait is called evolutionary conservation. It indicates that even slight variations in these molecules result in cells that either could not thrive or would reproduce and cause damage and evolutionary penalties to the organism.

All The Science is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.

All The Science, in your inbox

Our latest articles, guides, and more, delivered daily.