Javad Jamshidi Fasa University of Medical Sciences, November 2015 Gene Structure and Transcriptio n

How cells decode and use the information in their genomes? The DNA in genomes uses RNA as an intermediary Transcription  Translation (Central Dogma) 2

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Unit of DNA that contains the information to specify synthesis of a single polypeptide chain or functional RNA The vast majority of genes are protein coding genes There are many other genes which don’t code proteins 4

DNA  Transcription  RNA 5

Sense or Non-template Antisense or Template strand 6

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Transcription region Translated region Promoter 5´UTR and 3´UTR Upstream, Downstream 8

The process by which information from a gene is used in the synthesis of a functional gene product This could be a protein or some functional RNA The difference between various cells in a specific organism is due to difference in gene expression 9

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Transcription begins with the opening and unwinding of a small portion of the DNA double helix One of the two strands of the DNA double helix acts as template The RNA nucleotide sequence is determined by the complementary base- pairing Catalyzed by RNA polymerases, add rNTPs 11

Always 5´  3´ RNA polymerases can start an RNA chain without a primer About one mistake for every 10 4 nucleotides 12

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After 20 to 30 nucleotides have been transcribed Protect the RNA transcript from degradation by endogenous cellular exonucleases Facilitate transport of the mRNA to the cytoplasm and attachment to the ribosomes 19

Approximately 200 adenylate residues-the so-called poly(A) tail-are added to the mRNA, Facilitates nuclear export and translation 20

TYPE OF RNAFUNCTION mRNAsmessenger RNAs, code for proteins rRNAs ribosomal RNAs, form the basic structure of the ribosome and catalyze protein synthesis tRNAs transfer RNAs, central to protein synthesis as adaptors between mRNA and amino acids snRNAs small nuclear RNAs, function in a variety of nuclear processes, including the splicing of pre-mRNA snoRNAs small nucleolar RNAs, used to process and chemically modify rRNAs miRNAs microRNAs, regulate gene expression typically by blocking translation of selective mRNAs siRNAs small interfering RNAs, turn off gene expression by directing degradation of selective mRNAs and the establishment of compact chromatin structures Other noncoding RNAs function in diverse cell processes, including telomere synthesis, X-chromosome inactivation, and the transport of proteins into the ER

Transcription Initiation in Eukaryotes Requires Many Proteins RNA Polymerase II Requires General Transcription Factors (TFIIs) Eukaryotic transcription initiation must deal with the packing of DNA 24

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