When chromatin is treated with non specific neucleases, what is the length of the resulting pieces of DNA
Answers
Explanation:
The haploid human genome contains approximately 3 billion base pairs of DNA packaged into 23 chromosomes. Of course, most cells in the body (except for female ova and male sperm) are diploid, with 23 pairs of chromosomes. That makes a total of 6 billion base pairs of DNA per cell. Because each base pair is around 0.34 nanometers long (a nanometer is one-billionth of a meter), each diploid cell therefore contains about 2 meters of DNA [(0.34 × 10-9) × (6 × 109)]. Moreover, it is estimated that the human body contains about 50 trillion cells—which works out to 100 trillion meters of DNA per human. Now, consider the fact that the Sun is 150 billion meters from Earth. This means that each of us has enough DNA to go from here to the Sun and back more than 300 times, or around Earth's equator 2.5 million times!
Each nucleosome is composed of DNA wound 1.65 times around eight histone proteins. Nucleosomes fold up to form a 30-nanometer chromatin fiber, which forms loops averaging 300 nanometers in length.
- The amount of DNA per nucleosome was determined by treating chromatin with an enzyme that cuts DNA (such enzymes are called DNases).
- One such enzyme, micrococcal nuclease (MNase), has the important property of preferentially cutting the linker DNA between nucleosomes well before it cuts the DNA that is wrapped around octamers.
- By regulating the amount of cutting that occurs after the application of MNase, it is possible to stop the reaction before every linker DNA has been cleaved. At this point, the treated chromatin will consist of mononucleosomes, dinucleosomes, trinucleosomes, and so forth.
- If DNA from MNase-treated chromatin is then separated on a gel, a number of bands will appear, each having a length that is a multiple of mononucleosomal DNA.
- The simplest explanation for this observation is that chromatin possesses a fundamental repeating structure.