|WEEK 5 & 6: LAB BIOS390 transcription in prokaryotes |isolate Plasmid DNA

WEEK 5: LAB: transcription in prokaryotes Transcription is the first step in gene expression. It involves copying a gene's DNA sequence to make an RNA molecule. Before transcription can take place, the DNA double helix must unwind near the gene that is getting transcribed. The region of opened-up DNA is called a transcription bubble. Transcription uses one of the two exposed DNA strands as a template; this strand is called the template strand. The RNA product is complementary to the template strand and is almost identical to the other DNA strand, called the nontemplate (or coding) strand. However, there is one important difference: in the newly made RNA, all the T nucleotides are replaced with U nucleotides. The site on the DNA from which the first RNA nucleotide is transcribed is called the +1 site, or the initiation site. Nucleotides that come before the initiation site are given negative numbers and said to be upstream. Nucleotides that come after the initiation site are marked with positive numbers and said to be downstream.