Answer to Question #277433 in Biochemistry for osc

Question

1. What is "junk DNA"? Does if vary across different organisms? Explain.

Answer 1

Only about 1 percent of DNA is made up of protein-coding genes; the other 99 percent is noncoding. Noncoding DNA does not provide instructions for making proteins. Scientists once thought noncoding DNA was “junk,” with no known purpose.Some of this noncoding DNA is used to produce noncoding RNA components such as transfer RNA, regulatory RNA and ribosomal RNA.

A new study led by researchers at University of California, Berkeley, and Washington University explored the function of one component of this junk DNA, transposons, which are selfish DNA sequences able to invade their host genome. The study shows that at least one family of transposons -- ancient viruses that have invaded our genome by the millions -- plays a critical role in viability in the mouse, and perhaps in all mammals. When the researchers knocked out a specific transposon in mice, half their mouse pups died before birth.

This is the first example of a piece of "junk DNA" being critical to survival in mammals.

University, and his colleagues discovered that during vertebrate evolution, a novel retroposon—a DNA fragment, reverse-transcribed from RNA, that can insert itself anywhere in the genome—was exapted as an enhancer, a signal that increases a gene's transcription. On the other hand, anonymous sequences that are nonfunctional in one species may, in another organism, become an exon—a section of DNA that is eventually transcribed to messenger RNA.