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Chapter 3 – DNA Structure & Transcription (Production of RNA)DNA structure, Transcription, Processing of eukaryotic transcriptsPart 1: DNA StructureI. DNA A. General1. “Information molecule”: musta. contain necessary informationb. be passed to offspringc. be variable, but still accurate (ex. binary)2. Reminder: DNA is a polymer of nucleotidesB. Terminology1. Nucleotide vs. Nucleoside a. Nucleoside = sugar + baseb. Nucleotide = sugar + base + at least 1 phosphatei. 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 Backbone1. Linear strand of alternating phosphate & sugar groups2. Nonvariable3. Negatively charged 4. Tail-end phosphate (not connected to a sugar) will beHPO4 (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 directionB. Base Sequence1. Variable part of DNA – holds info2. Absolutely no constraints on what bases are in what orderC. Double-helix (for BDNA – only DNA we talk about)1. 2 antiparallel strands in a double helix2. 2 strands stay together by H-bonds that form between complimentary bases (1 purine—1 pyrimidine)a. A-T, G-Ci. This specificity is what keep width of DNA constantb. Bases also interact noncovalently with the ones above & below and “stack” (tightly group), which stabilizes helixi. **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 chromatin1. *Don’t worry about H2A, H2B, etc. in the bookPart 2: Transcription – Making an RNA Product From a GeneI. General A. “Gene” – sequence of DNA that codes for a product, and its associated control regions II. 1 scenario of gene structure (eukaryote): III. Process of Transcription A. Specific proteins associate with the controlregions of a gene (ex. start/stop) (fig. 3.17) B. RNA polymerase complex separates theDNA strands to form the “transcriptionbubble” (fig. 3.18)C. 1 DNA strand (half-strand) used to buildRNA1. 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 basepairing & catalyzes pyrophosphate release &phosphodiester bond formation (3.19)E. If the transcript contains information tobuild a protein, it’s mRNA (messenger RNA)1. Prokaryotes can immediately use mRNAto build proteins 2. Eukaryotes first process mRNA because some of the transcript isn’t useful (introns/exons splicing)Can be a gap between enhancer & rest:-DNA sequence that gets transcribed-Terminator: ends transcription Promoter: general transcription factors bind hereEnhancer Sequence: transcriptional activator proteins bind hereIV. Splicing (Introns/Exons) A. The –DNA sequence that gets transcribed- above contains introns (useless) and exons (useful)B. mRNA processing1. Adds special nucleotide to the 5’ end (5’ cap)2. Adds poly-A (adenine) tail to 3’ end3. Removes introns & covalently bond exons togethera. One eukaryotic transcript can be processed different ways (fig. 3.25)b. Splicepsomes (snRNP’s) – RNA & protein machines used to remove introns4. Remember, not all transcripts are mRNA.a. rRNA (ribosomal)b. tRNA (transfer)c. small nuclear (snRNA)d. micro RNA


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UD BISC 207 - Chapter 3 – DNA Structure

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