Describe how long strands of

Two types of base pairing occur: nucleotide A pairs with T, and nucleotide C pairs with G. Further Exploration Concept Links for further exploration helicase phosphate backbone nucleic acid DNA phosphate backbone replication. Related Concepts 6. You have authorized LearnCasting of your reading list in Scitable. Do you want to LearnCast this session?

DNA is a long, floppy molecule, and there's more than three feet of it in every cell. Scientists from the department of Biochemistry and Biophysics at the University of Rochester School of Medicine and Dentistry worked with colleagues in France and Japan to describe the first step of DNA packing in a cell. They provided the first-ever detailed picture of the most basic building block of chromosomes, known as the nucleosome, and found that a protein known as H1 for linker histone H1 helps DNA become more compact and rigid within the nucleosome.

In contrast, when H1 isn't present, the DNA is loose and flexible. The tight structure that H1 creates helps shield our DNA from various factors that can activate or "turn on" certain genes. Without H1, DNA is more accessible to factors that could trigger disease-causing genes.

Published in the journal Molecular Cell , this finding will inform research on all processes that involve chromosomes, such as gene expression and DNA repair, which are critical to the understanding of diseases such as cancer, according to Jeffrey J.

Hayes, Ph. The teams in France and Japan used specialized microscopes and X-rays to capture pictures of DNA molecules interacting with H1 and other key proteins. Because of the size of the DNA and protein molecules, the pictures generated by these techniques were fuzzy and difficult to analyze. Lead study author Amber Cutter, a graduate student in Hayes' lab, put all of the components -- DNA, H1, and other proteins -- together in tiny test tubes and conducted various biochemical experiments. An important property of DNA is that it can replicate, or make copies of itself.

Each strand of DNA in the double helix can serve as a pattern for duplicating the sequence of bases. This is critical when cells divide because each new cell needs to have an exact copy of the DNA present in the old cell. Other chapters in Help Me Understand Genetics.

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