© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko PowerPoint Lectures for Campbell Biology: Concepts & Connections, Seventh Edition Reece, Taylor, Simon, and Dickey Chapter 10 Molecular Biology of the Gene

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  Translation is the synthesis of proteins under the direction of RNA. © 2012 Pearson Education, Inc. Used in translation of mRNA

Figure 10.7 DNA molecule Gene 1 Gene 2 Gene 3 A Transcription RNA TranslationCodon Polypeptide Amino acid AAC C GG C AAAA UU GGCCG UUUU DNA U

Figure 10.8B_s3 T Strand to be transcribed A C T TC A A A A A T DNA AA T C T T T T GAG G RNA Transcription AAAA U U U U U G G G Translation Polypeptide MetLysPhe Stop codon Start codon RNA is complementary to ONE DNA strand!

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:1 amino acid may be coded for by more than 1 codon.  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 Second base Third base First base

Transcription: DNA to RNA  Location = Nucleus in Eukaryotes  RNA Polymerase links RNA nucleotides together © 2012 Pearson Education, Inc. Animation: Transcription

Figure 10.9B_1 RNA polymerase DNA of gene Promoter DNA Initiation 1 Terminator DNA Promoter = DNA sequence that marks beginning of gene RNA Polymerase binds DNA at promoter and transcription begins

Figure 10.9B_2 2 Elongation Growing RNA RNA Polymerase synthesizes RNA using ONE DNA strand as a template.

RNA polymerase Free RNA nucleotides Template strand of DNA Newly made RNA Direction of transcription T G A G G A A U C CA C T T A A C C G G U T U T A ACC T A T C Note: RNA synthesized using base pair rules!! (A-U and G-C) Only ONE strand of DNA is ‘read’!

Termination RNA polymerase Completed RNA 3 Growing RNA Transcription STOPS at terminator -- RNA polymerase detaches from DNA. Terminator = DNA sequence that marks end of gene

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 DNA Cap Exon IntronExon RNA transcript with cap and tail ExonIntron Transcription Addition of cap and tail Introns removed Tail Exons spliced together Coding sequence NUCLEUS CYTOPLASM mRNA