Transcription Packet #10 Chapter #8

Introduction Transcription Transcription is a process that occurs within the nucleus of a cell where a single strand of DNA is used to produce a complementary strand of RNA. The type of RNA produced is mRNA.

Types of RNA mRNA Messenger RNA An RNA molecule transcribed from the DNA of a gene Once mRNA is complete, proteins are translated from mRNA by the help of RIBOSOMES Types of RNA mRNA snRNA tRNA rRNA

The Gene

Chromosome Review DNA strands are composed of segments known as genes. Chromatin DNA Molecules DNA Strands Genes

Genes Genes, used during the process of transcription, have two major segments. Regulatory region Coding region Both regions play a role during transcription. Within the regulatory region, there is a special region known as the promoter region. DNA Strands Genes Regulatory Region Promoter Region Coding Region Terminator

Strands of Transcription Template Strand In transcription, known as the Complementary Strand (cDNA) A molecular “mold” that shapes the structure or sequence of another molecule Controls the nucleotide sequence of RNA during transcription Alignment guide “GUIDE”

Strands of Transcription Complementary Strand (cDNA) DNA transcribed from a specific RNA strand Complementary Strand (cRNA) RNA transcribed from a specific DNA single-stranded template

Transcription The Process

The Process RNA Polymerase, the only enzyme used during transcription, binds at the promoter region (sequence) and unzips the DNA strand RNA Polymerase works downstream adding RNA nucleotides to the 3’ end of the newly formed RNA strand New RNA strand grows in the 5’ to 3’ direction RNA Polymerase hits the “Terminator” sequence that signals the end of transcription Newly made RNA is released. This RNA is called pre-mRNA.

Post-Transcription

Post-Transcription I The new RNA strand is called pre-mRNA Why? Because the pre-mRNA needs to be “groomed” for the moment of Translation Unneeded RNA nucleotide segments, known as introns, need to be removed.

Post-Transcription II The introns are removed and the exons, the good regions, are joined together in a process known as splicing. Process completed using the enzyme known as spliceosome. Spliceosome contains snRNA. The completed mRNA leaves the nucleus and enters into the cytoplasm ready for translation. The mRNA carries the genetic code with it. Pre-mRNA contains both introns and exons. Introns The “Junk in the Trunk” Regions of the RNA strand that must be removed, via splicing, and will not be used during Translation Exons Regions of RNA that WILL be used and translated into amino acids during TRANSLATION

Review