Why is dna coiled up

The second level of packaging DNA happens when the string of DNA and nucleosomes crunch together to form a thick fiber. This fiber is 30 nanometers in diameter, and is referred to as the nanometer fiber.

This fiber then folds on itself to form loops along a rod of proteins, like branches growing out from a tree trunk. This tree trunk structure then takes on a helical shape, like that of a telephone cord. DNA is so long that the helical coil itself becomes like a big fiber, which can be coiled again.

The density of a chromosome is like that of many cords coiled into a circle and stacked together in large crates, which are shipped in cargo containers pulled by wheeled trucks -- but in a chromosome, all the cords are connected. Human chromosomes have similarities in their structure. Near the middle of the chromosome is a region of proteins called the centromere.

The centromere is like a strong belt. During cell division, when chromosomes are pulled apart into two cells, they are pulled by their centromeres. Pulling the strong centromere, not other parts of the chromosome, reduces the chance of breaking the chromosome. The ends of human chromosomes contain stretches of DNA called telomeres. Telomeres do not contain genes, but are shortened every time the cell divides.

They exist to protect the genes further in on the chromosome, because the chromosome shortens a bit after each cell division. Nicholas Cozzarelli of the University of California, Berkeley, and colleagues show that this protein called 13S condensin can make DNA twist up into positive supercoils. Researchers know that this protein somehow completes the job, but, until now, no one had any idea how.

Unlike a phone cord, which, much to one? They also showed that condensin can do its thing only when the cell is getting ready to divide. At other times during the cell? You can also search for this author in PubMed Google Scholar. Reprints and Permissions. Wunsch, H. How DNA does the twist. Nature Download citation. Published : 05 August Anyone you share the following link with will be able to read this content:.

Sorry, a shareable link is not currently available for this article. In all living things, from plants and animals to microbes, these instructions tell cells which molecules to make. That reemitted light is known as a fluorescence. Offspring inherit genes from their parents. Genes influence how an organism looks and behaves. The field of science dealing with these biological instructions is known as genetics.

People who work in this field are geneticists. Strands of DNA coil around sets of eight of these proteins to fit inside of cells. Each chromosome within a cell has its own strand of DNA. So with 23 pairs of human chromosomes, every human cell should host 46 strands of DNA — each wrapped around hundreds of thousands of histones. This tight coiling helps the body to pack its long DNA molecules into very tiny spaces.

Molecules can be made of single types of atoms or of different types. For example, the oxygen in the air is made of two oxygen atoms O 2 , but water is made of two hydrogen atoms and one oxygen atom H 2 O. Some mutations occur naturally. Others can be triggered by outside factors, such as pollution, radiation, medicines or something in the diet. A gene with this change is referred to as a mutant. The hundreds of thousands of nucleosomes found on a single strand of DNA help to pack the DNA into a very small space.

Typically a single rounded structure encased within a membrane, the nucleus contains the genetic information. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. The hemoglobin in blood and the antibodies that attempt to fight infections are among the better known, stand-alone proteins.

Medicines frequently work by latching onto proteins. They are represented by the letters A,C,T and G.