Chapter 3 DNA Structure Transcription Production of RNA DNA structure Transcription Processing of eukaryotic transcripts Part 1 DNA Structure I DNA A General 1 Information molecule must a contain necessary information b be passed to offspring c be variable but still accurate ex binary 2 Reminder DNA is a polymer of nucleotides B Terminology 1 Nucleotide vs Nucleoside a Nucleoside sugar base b Nucleotide sugar base at least 1 phosphate i Can be identified as nucleoside mono di tri phosphate II Structure 2 nucleotides are linked by series of covalent bonds called a phosphodiester bond C O P O C A The Backbone 1 Linear strand of alternating phosphate sugar groups 2 Nonvariable 3 Negatively charged 4 Tail end phosphate not connected to a sugar will be HPO4 H attached to top O instead of PO4 see diagram 5 All sugars in strand are oriented in same direction 5 3 or 3 5 6 Strand has polarity or direction B Base Sequence 1 Variable part of DNA holds info 2 Absolutely no constraints on what bases are in what order C Double helix for BDNA only DNA we talk about 1 2 antiparallel strands in a double helix 2 2 strands stay together by H bonds that form between complimentary bases 1 purine 1 pyrimidine a A T G C i This specificity is what keep width of DNA constant b Bases also interact noncovalently with the ones above below and stack tightly group which stabilizes helix i clicker question unrelated Make sure the Oxygen on the 3 carbon isn t there if you re working in DNA D IN the cell DNA is coiled packaged with proteins The 2 together are called chromatin 1 Don t worry about H2A H2B etc in the book Part 2 Transcription Making an RNA Product From a Gene I General A Gene sequence of DNA that codes for a product and its associated control regions II 1 scenario of gene structure eukaryote Terminator ends transcription Can be a gap between enhancer rest DNA sequence that gets transcribed Enhancer Sequence transcriptional activator proteins bind here Promoter general transcription factors bind here III Process of Transcription A Specific proteins associate with the control regions of a gene ex start stop fig 3 17 B RNA polymerase complex separates the DNA strands to form the transcription bubble fig 3 18 C 1 DNA strand half strand used to build RNA 1 RNA built from its 5 to 3 end so from 3 to 5 on the half strand of the DNA D RNA polymerase checks for correct base pairing catalyzes pyrophosphate release phosphodiester bond formation 3 19 E If the transcript contains information to build a protein it s mRNA messenger RNA 1 Prokaryotes can immediately use mRNA to build proteins introns exons splicing 2 Eukaryotes first process mRNA because some of the transcript isn t useful IV Splicing Introns Exons A The DNA sequence that gets transcribed above contains introns useless and exons useful B mRNA processing 1 Adds special nucleotide to the 5 end 5 cap 2 Adds poly A adenine tail to 3 end 3 Removes introns covalently bond exons together a One eukaryotic transcript can be processed different ways fig 3 25 b Splicepsomes snRNP s RNA protein machines used to remove introns 4 Remember not all transcripts are mRNA a rRNA ribosomal b tRNA transfer c small nuclear snRNA d micro RNA miRNA
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