Transcription of genes

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  1. Transcription of genes is controlled by transcription factors that bind to DNA sequences in the regulatory regions of genes
    1. regions are most commonly upstream (5’) of the transcription start site and are referred to as promoters
      1. minimal promoter usually consists of the TATA box which binds TATA binding protein that starts the transciption process
    2. transciption termination signals reside downstream (3’) of a gene
      1. termination signals such as AAUAAA at the 3’ end of the mRNA designate the site for polyadenylation, a process that influences mRNA transport to the cytoplasm, stability and translational efficiency
  2. Exons refer to portions of genes that are eventually spliced together to form mRNA; introns refer to the spacing regions between the exons that are spliced out of precursor RNAs during RNA processing
  3. transcription activation and repression
    1. RNA transcription begins when RNA polymerase II begins at a DNA sequence start site which is approximately 25 nucleotides downstream from the TATA box
      1. RNA polymerase II initiates separation of the DNA strands using one strand in a 5’ to 3’ direction at a rate of 30 nucleotides per second until a stop codon is reached
  4. Translation
    1. begins with initiation factors that bind to a special tRNA called methionyl initiation tRNA; this complex binds to the 40s ribosome; this entire complex then binds to mRNA until the triplet AUG is identified which is a universal signal for starting translation; once the AUG is identified the 60s ribosome binds and protein synthesis begins
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