1. 11/14/08
Lecture 29 - Molecular Genetics 4
 Promoter (regions): regions where RNA polymerase binds.
 In Eukaryotic cells, promoter contain a sequence of nucleotides called TATA (DNA) box.
 Transcription factors bind to the promoter before the RNA polymerase can bind.
 Termination
 Prokaryotic cells
 The termination sequence is in the DNA.
 When RNA polymerase detaches from DNA.
 The mRNA is released (going to the ribosomes).
 Eukaryotic cells
 RNA polymerase continues transcription beyond the coding section of the gene (adding a non-
coding signal, usually being AAUAAA).
 In the prokaryotic cell, mRNA goes directly to the ribosome.
 In the eukaryotic cell, two kinds of mRNA exist, pre-mRNA and final mRNA.
 Pre-mRNA has to be proceeded and edited (all happening in the nucleus) to make final mRNA.
 - Split genes: many sequences are removed from the pre-mRNA.
 Introns: the pieces of the mRNA strand that are removed.
 Exons: the pieces of the mRNA that are used in the final mRNA.
 Both (5' and 3') ends of the mRNA strand are modified.
 A modified “guanine cap” is added to the 5' end.
 A “poly A tail” is added to the 3' end.
 Final mRNA is sent from the nucleus to the ribosome.
 Translation
 Transfer RNA (tRNA) is needed for translation.
There are many kinds of tRNA. There is 1 tRNA for each codon; the total is 61 tRNA molecules.
 An anticodon is attached to the bottom loop of the tRNA molecule.
 Ribosomes
 Ribosomes are necessary in prokaryotic and eukaryotic cells.
 They are where polypeptide chains are assembled.
 Ribosomes consist of 2 sub-units (large and small)
 rRNA (ribosomal RNA) consist of RNA and a ribosomal protein