Transcription 2024 PDF

Nov, 2024  Transcription Structure of nucleic acids DNA replication and repair Transcription Translation, synthesis of protein https://www.youtube.com/watch?v=WsofH466lqk https://www.youtube.com/watch?v=-AnsJILjbz8 – HHMi 1:55 Usually every gene contains 2...

Nov, 2024  Transcription Structure of nucleic acids DNA replication and repair Transcription Translation, synthesis of protein https://www.youtube.com/watch?v=WsofH466lqk https://www.youtube.com/watch?v=-AnsJILjbz8 – HHMi 1:55 Usually every gene contains 2 types of information 1.Specifies the primary structure of the final product 2.Critical for regulated expression of the gene’s product  Gene expression begins with Transcription – the DNA-directed synthesis of RNA To produce an mRNA 2 things need to be identified a gene sequence on DNA Information necessary for the exact start site Messenger RNA (mRNA) Carries genetic Transfer RNA (tRNA) info from DNA to - -functions cytosol for Ribosomal MicroRNA (miRNA) in protein translation RNA (rRNA) -transcribed but not synthesis- carries aas translated  Structure of a typical eukaryotic gene The minimum linear sequence of genomic NA that encode proteins and structural RNA is termed a GENE Composed of 1. Coding exons 2. Non coding introns 3. Non coding consensus sequences (serve as recognition markers & are conserved) a) promoters b) splice acceptor and donor sequences Intron (and of course exon) no, size, location and sequence differ from gene to gene Promoters: DNA sequences that select/determine the start site of RNA synthesis Consensus sequence for promoters typically has the sequence “TATA” and is often located 15-30 bp upstream from the transcription start site – the TATA box Other sequences require for promotor function include the CAAT box and the GC box In eukaryotes, proteins known as transcription factors bind to the TATA box and facilitate the binding of RNA polymerase 11  PRIMARY RNA TRANSCRIPT Splice acceptor and donor sequences: Type of consensus sequence found at the 5’ and 3’ ends of introns Introns often begin with GU and end with AG and are preceded by a pyrimidine-rich tract This consensus sequence is essential for splicing introns out of the primary transcript  Features of Transcription Selective Only parts of the genome are transcribed at any particular time in any particular cell Primary RNA transcripts are modified mRNA processing https://www.youtube.com/watch?v=YjWuVrzvZYA  RNA Synthesis Occurs in nucleus Catalyzed by an RNA polymerase Protein encoding genes produce mRNA as an intermediate Regulatory mRNA sequences are important for the stability and translational efficiency of the process Regulatory mRNA sequences are in the 5’ and the 3’ ends of the mRNA – called the untranslated regions (UTR) and are not part of the final product The initial mRNA is thus edited/processed 1. RNA polymerases: several in eukaryotic cells 2. Several proteins bind to the gene to be transcribed: preinitiation complex accurately positions RNA pol on DNA for initiation 3. Regulatory regions: an mRNA producing gene can be divided into coding and regulatory regions. The regulatory regions consists of 2 classes of sequences a) Those that ensure basal expression b) Those where expression is regulated 4.Basal transcription complex formation: requires a number of transcription factors 5. A ssRNA is produced from a dsDNA  Newly synthesised RNA is complementary to DNA template strand 5’ 3’ 3’ 5’ Formation of the transcription complex requires several proteins in addition to RNA polymerase 11  RNA Processing Gene transcription produces an RNA that is larger than the mRNA found in the cytoplasm for translation -Primary transcript- contains segments of transcribed introns -Introns are removed and exons joined to form mature mRNA -“Capped and tailed” Addition of a 5’ cap: by a methyl guanosine residue 1. Addition of a 5’ cap: by a methyl guanosine residue This protects it from degradation Helps transcript bind to the ribosome during protein synthesis 2. Addition of a poly(A) tail Primary transcripts contain a highly conserved AAUAAA consensus sequence, known as a polyadenylation signal near their 3’ end This is recognized by a specific endonuclease that cleaves the RNA approx 20 nucleotides downstream 3. Intron Removal Splice sites are present within the gene that delineate the intron A Spliceosome – converts primary transcript into mRNA Spliceosome comprise A) the primary transcript B)5 small nuclear RNAs and C) > 50 proteins snRNPs (“snurps”) The mature RNA leave nucleus and passes into the cytoplasm through the nuclear pores  4. Alternative splicing of genes to generate multiple proteins Alternative splicing: Genes form multiple proteins by joining different exon segments in the primary transcript Cell specific regulation May explain why the human genome has fewer genes than expected Inactivation of prokaryotic RNA by rifampin Rifampin present Rifampin - Important in the treatment of Tuberculosis Actinomycin D – the 1st antibiotic to have therapeutic application in tumor chemotherapy –intercalates between the bases and inhibits transcription initiation and elongation  MUTATIONS IN SPLICING CAUSE HUMAN DISEASE Thalassemias Hereditary anemias The single most common genetic disorder in the world Mutations affect synthesis of either the a or b chains of globin –decreased production of hemoglobin Point mutations can occur with the TATA box or mutations can occur in the splice junction sequences at the intron-exon boundaries