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Chapter 10 Molecular Biology of the Gene PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey © 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko FROM DNA TO PROTEIN Part 1: Transcription © 2012 Pearson Education, Inc. Genes Determine the Production of RNA and Proteins Gene = a DNA sequence that specifies an RNA or protein sequence Transcription is the synthesis of RNA under the direction of DNA. DNA mRNA (recipe for protein’s amino acid seq) DNA tRNA DNA rRNA Used in translation of mRNA Translation is the synthesis of proteins under the direction of RNA. © 2012 Pearson Education, Inc. Figure 10.7 DNA molecule Gene 1 Gene 2 Gene 3 DNA A A A C C G G C A A A A Transcription RNA Translation U U U G G C Codon Polypeptide Amino acid C G U U U U Figure 10.8B_s3 Strand to be transcribed T A C T T C A A A A T C DNA A T G A A G T Transcription RNA T T T A G RNA is complementary to ONE DNA strand! A U G A A G U U U U A G Translation Start codon Polypeptide Met Stop codon Lys Phe The Genetic Code Codon is a 3-nucleotide sequence in mRNA that specifies an amino acid Genetic Code is: Triplet: 3 nucleotides = 1 amino acid (This allows for 64 possible codons) Redundant: codon. 1 amino acid may be coded for by more than 1 Ex: 4 codons = proline Specific: Only 1 amino acid per codon Ex: CCU only = proline Universal: Every organism uses the same genetic code!!!!! © 2012 Pearson Education, Inc. Figure 10.8A Third base First base Second base Transcription: DNA to RNA Location = Nucleus in Eukaryotes RNA Polymerase links RNA nucleotides together Animation: Transcription © 2012 Pearson Education, Inc. Figure 10.9B_1 RNA polymerase Terminator DNA DNA of gene Promoter DNA Promoter = DNA sequence that marks beginning of gene 1 Initiation RNA Polymerase binds DNA at promoter and transcription begins Figure 10.9B_2 2 Elongation RNA Polymerase synthesizes RNA using ONE DNA strand as a template. Growing RNA Note: RNA synthesized using base pair rules!! (A-U and G-C) Free RNA nucleotides RNA polymerase C C A A Only ONE strand of DNA is ‘read’! A U C C A T A G G T Direction of transcription Newly made RNA T Template strand of DNA Transcription STOPS at terminator -- RNA polymerase detaches from 3 DNA. Completed RNA Growing RNA Termination Terminator = DNA sequence that marks end of gene RNA polymerase Eukaryotic RNA is processed before leaving the nucleus as mRNA Messenger RNA (mRNA) – encodes amino acid sequences for a protein In prokaryotes transcription and translation occur in the same place But in eukaryotes, mRNA must exit the nucleus to enter the cytoplasm (site of translation). – Eukaryotic mRNA has – introns, non-coding, interrupting sequences – exons, the coding regions. © 2012 Pearson Education, Inc. Eukaryotic RNA is processed before leaving the nucleus as mRNA 5’ cap Modified G nucleotide added to 5’ end 3’ poly A tail Long sequence of A nucleotides added to 3’ end – facilitate the export of the mRNA from the nucleus, – protect the mRNA from destruction, and – help ribosomes bind to the mRNA. RNA splicing removes introns and joins exons to produce a continuous coding sequence. © 2012 Pearson Education, Inc. Figure 10.10 Exon Intron Exon Intron Exon DNA Cap RNA transcript with cap and tail Transcription Addition of cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence NUCLEUS CYTOPLASM