* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lecture Notes with Key Figures PowerPoint - HMartin
Survey
Document related concepts
Deoxyribozyme wikipedia , lookup
Polyadenylation wikipedia , lookup
Nucleic acid analogue wikipedia , lookup
Expanded genetic code wikipedia , lookup
Non-coding RNA wikipedia , lookup
Promoter (genetics) wikipedia , lookup
Gene expression wikipedia , lookup
Messenger RNA wikipedia , lookup
Silencer (genetics) wikipedia , lookup
Epitranscriptome wikipedia , lookup
Genetic code wikipedia , lookup
Eukaryotic transcription wikipedia , lookup
Transcript
PowerPoint® Lecture Presentation for Concepts of Genetics Ninth Edition Klug, Cummings, Spencer, Palladino Chapter 14 The Genetic Code and Transcription Lectures by David Kass with contributions from John C. Osterman. Copyright © 2009©Pearson Education, Inc. Copyright 2009 Pearson Education, Inc. Section 14.1 • The genetic code is: • written in linear form – composed of mRNA • RNA derived from complementary bases in DNA • In mRNA, triplet codons specify 1 amino acid • code contains “start” and “stop” signals • unambiguous • degenerate • commaless • nonoverlapping • nearly universal Copyright © 2009 Pearson Education, Inc. Section 14.4 • Genetic code is degenerate, w/many amino acids specified by more than one codon. • Only tryptophan and methionine are encoded by a single codon. Copyright © 2009 Pearson Education, Inc. Section 14.4 • Wobble hypothesis predicts that hydrogen bonding between the codon and anticodon at the third position is subject to modified base-pairing rules. Copyright © 2009 Pearson Education, Inc. Section 14.4 • The genetic code shows order in that chemically similar amino acids often share one or two middle bases in the triplets encoding them. Copyright © 2009 Pearson Education, Inc. Section 14.4 • The initial amino acid incorporated into all proteins is a modified form of methionine—N-formylmethionine (fmet). (in bacteria) • AUG is the only codon to encode for methionine. • Initiator codon • When AUG appears internally in mRNA, an unformylated methionine is inserted into the protein. Copyright © 2009 Pearson Education, Inc. Section 14.4 • Three codons (UAG, UAA, and UGA) serve as termination codons and do not code for any amino acid. Copyright © 2009 Pearson Education, Inc. Section 14.6 • The Genetic Code Is Nearly Universal • Mitochondrial DNA revealed some exceptions to the universal genetic code. Copyright © 2009 Pearson Education, Inc. Section 14.7 • In some viruses, overlapping genes have been identified in which initiation at different AUG positions out of frame with one another leads to distinct polypeptides. Copyright © 2009 Pearson Education, Inc. Section 14.8 • mRNA serves as the intermediate molecule between DNA and proteins. • mRNA is synthesized on a DNA template during transcription. Copyright © 2009 Pearson Education, Inc. http://ichristianschool.org/images/mrna.gif Section 14.10 • RNA polymerase directs the synthesis of RNA using a DNA template. • No primer is required for initiation • The enzyme uses ribonucleotides instead of deoxyribonucleotides. Copyright © 2009 Pearson Education, Inc. Section 14.10 • Transcription begins with template binding by RNA polymerase at a promoter. • The s subunit is responsible for promoter recognition (in bacteria). Copyright © 2009 Pearson Education, Inc. Section 14.10 • Transcription begins at the transcription start site, where the DNA double helix is unwound to make the template strand accessible. Copyright © 2009 Pearson Education, Inc. Section 14.10 • E. coli promoters have two consensus sequences, TTGACA and TATAAT, positioned at –35 and –10 with respect to the transcription initiation site. Copyright © 2009 Pearson Education, Inc. Section 14.10 • Once initiation has been completed with the synthesis of the first 8–9 nucleotides, sigma (s) dissociates and elongation proceeds with the core enzyme. Copyright © 2009 Pearson Education, Inc. Section 14.10 • At the end of the gene, transcription terminates due to hairpin formation in the RNA. • In some cases, termination depends on the rho () termination factor. Copyright © 2009 Pearson Education, Inc. Section 14.11 • Transcription in Eukaryotes Differs from Prokaryotic Transcription in Several Ways • Occurs in nucleus and is not coupled to translation. • Requires chromatin remodeling. • In addition to promoters, enhancers also influence transcription regulation. • Eukaryotic mRNAs require processing to produce mature mRNAs. Copyright © 2009 Pearson Education, Inc. Eukaryotes possess three forms of RNA polymerase, each of which transcribes different types of genes. Copyright © 2009 Pearson Education, Inc. Table 14.7 Section 14.11 • RNA polymerase II (RNP II) promoters have a core promoter element and promoter and enhancer elements. • The TATA box is a core promoter element that binds the TATA-binding protein (TBP) of transcription factor TFIID and determines the start site of transcription. • CAAT box Copyright © 2009 Pearson Education, Inc. Section 14.11 • General transcription factors are required for all RNP II mediated transcription and help RNA polymerase II bind to the promoter and initiate transcription. Copyright © 2009 Pearson Education, Inc. Section 14.11 • Heterogeneous nuclear RNA (hnRNA) is posttranscriptionally processed by the addition of a 5' cap and a poly-A tail. • Introns are removed by splicing. • Exons spliced together. Copyright © 2009 Pearson Education, Inc. Section 14.12 • Introns (intervening sequences) are regions of the initial RNA transcript that are not expressed in the amino acid sequence of the protein. • Introns are removed by splicing and the exons (expressed) are joined together in the mature mRNA. • The size of the mature mRNA is usually much smaller than that of the initial RNA. Copyright © 2009 Pearson Education, Inc. Copyright © 2009 Pearson Education, Inc. Figure 14.12 Copyright © 2009 Pearson Education, Inc. Table 14.8 Group 1 Introns Copyright © 2009 Pearson Education, Inc. Figure 14.13 Section 14.12 • Pre-mRNA introns are spliced out by the spliceosome in a reaction involving the formation of a lariat structure. Copyright © 2009 Pearson Education, Inc. 14.13 Transcription Has Been Visualized by Electron Microscopy Copyright © 2009 Pearson Education, Inc. Figure 14.15