without introns (noncoded sections of DNA); however, there are many introns in eukaryotic DNA, interspersed between exons, which are the coded segments of DNA. A gene may consist of exons and introns with the introns ultimately spliced out of the RNA molecule or are not translated by the ribosomes. Genes contain a regulatory sequence that is necessary for their expression. There must be a promoter region on a gene that signals it is ready to be transcribed. There are transcription factors that attach to the promotor sequence along with RNA polymerase. There can be more than one promotor region per gene. There can be regulatory regions in the different genes. These alter the expression of the gene and will bind to transcription factors to cause the DNA to form a loop so that the transcribed region will be closer to the RNA polymerase binding site. There are things like enhancers that bind to activator proteins that make RNA polymerase more available and silencers that bind to repressor proteins to make DNA less available to RNA polymerase. What gets transcribed is called pre-RNA. There are many untranslated regions, such as those that contain ribosomal binding sites, terminator ends, and both start and stop codons. There are, particularly in eukaryotes, sequences of exons and introns that get spliced so that only the mature RNA will code for the protein. Prokaryotes are slightly different. Their genes are organized into operons, which code for multiple proteins at a time. They get transcribed as a continuous messenger RNA, called polycistronic mRNA. This is the scientific term for polygenic mRNA. While there are separate proteins made, they often are related to one another when it comes to the different functions they have in the cell, so they need to be regulated together.
GENE MUTATIONS Gene mutations can occur when genes are transcribed. The error rate in eukaryotic cells is very low; it is higher in RNA viruses. What this means is that, per generation in humans, about 1 to 2 new mutations occur.
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