Transcription Notes PDF

WE MAKE DOCTORS Transcription Ana Gabriela Colima Fausto, PhD Learning objectives Identify the elements that constitute a gene Describe the transcription process involved in the flow of genetic information Identify the proteins and consensus sequences involved in transcription as...

WE MAKE DOCTORS Transcription Ana Gabriela Colima Fausto, PhD Learning objectives Identify the elements that constitute a gene Describe the transcription process involved in the flow of genetic information Identify the proteins and consensus sequences involved in transcription as well as their functions Illustrate some current inhibitors of RNA synthesis Gene expression Although a chromosome carries hundreds or thousands of genes, only a fraction of these are in use at any given time. Different cells express different selections of genes depending on their specialized roles in the organism. Gene expression varies with the stage of development. Gene structure Eukaryotic genes are composed of coding exons, noncoding introns, and noncoding consensus sequences. Noncoding regions at the 5′ end to the first exon are referred to as upstream sequences and those at the 3′ end are called downstream sequences. Transcription RNA copy from a DNA strand 2 strands: Template, nontemplate(coding) RNA synthesis: 5’ to 3’ Only one strand is transcribed Not bidirectional Transcription Synthesis of RNA from DNA occurs in the nucleus and is catalyzed by an RNA polymerase RNA polymerase reads DNA 3' to 5' and produces an RNA molecule complementary to it Consensus sequence DNA recognition site. They are usually bound by proteins (transcription factors) and other regulatory proteins PROMOTERS DNA sequences that select or determine the start site of RNA synthesis.  Basal promoters: These sequences have two components. A proximal component (TATA box) and a distal component (CAAT and GC boxes). Enhancers and response elements (regulate gene expression): Enhance or repress expression (silencers), mediate the response to various signals including hormones and chemicals. Located upstream and downstream from the transcription start site.  TFIID (TBP + 8 to 10 TBP- associated factors): binds to the TATA box in the minor groove, it causes a bend in the DNA helix. TFIIF, has DNA helicase activity that promotes the unwinding of the DNA near the transcription start site RNA polymerase Inhibitors of RNA synthesis ✓Alpha-amanitin (α-AMA) is a toxin found in Amanita phalloides mushrooms that works by inhibiting RNA polymerase II in the liver, which leads to a protein deficiency and cell death. ✓Actinomycin D is a chemotherapeutic drug used to treat a number of types of cancer such as Wilms tumor, Ewing's sarcoma, testicular and certain types of ovarian cancer. It has the ability to inhibit transcription by binding DNA at the transcription initiation complex and preventing elongation of RNA chain by RNA polymerase Retroviruses Bibliography Chapter 8 Chandar, Nalini and Viselli, Susan. Lippincott's Illustrated Reviews: Cell and Molecular Biology, 2nd Edition Lippincott Williams & Wilkins, a Wolters Kluwer Health Publication, 2019.