Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The information constituting an organism’s genotype is carried in its sequence of bases THE FLOW OF GENETIC INFORMATION FROM DNA TO RNA TO PROTEIN The DNA genotype is expressed as proteins, which provide the molecular basis for phenotypic traits

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings A specific gene specifies a polypeptide –The DNA is transcribed into RNA, which is translated into the polypeptide Figure 10.6A DNA RNA Protein TRANSCRIPTION TRANSLATION

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The Evolution of Crick’s Central Dogma from the 1950s to today 1950’s DNA RNA Protein DNARNA Poly- peptide Splicing Alternative Splicing Phosphorylation Glycosylation Methylation Acetylation 1980’s DNA RNAPoly- peptide Splicing Alternative Splicing Other catalytic regulator RNAs MicroRNAs Editing Conformational Isomers Phosphorylation (up) Glycosylation Methylation (down) Acetylation (up) Other Histone modifications Other epigenetic factors Today

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The “words” of the DNA “language” are triplets of bases called codons –The codons in a gene specify the amino acid sequence of a polypeptide Genetic information written in codons is translated into amino acid sequences

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.7 DNA molecule Gene 1 Gene 2 Gene 3 DNA strand TRANSCRIPTION RNA Polypeptide TRANSLATION Codon Amino acid

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Virtually all organisms share the same genetic code Minor differences in the mito- chondria The genetic code is the Rosetta stone of life Figure 10.8A

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An exercise in translating the genetic code Figure 10.8B Start codon RNA Transcribed strand Stop codon Translation Transcription DNA Polypeptide Template strand or antisense - strand Coding Strand or Sense + strand

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Transcription produces genetic messages in the form of RNA Figure 10.9A RNA polymerase RNA nucleotide Direction of transcription Newly made RNA Template strand of DNA In eukaryotes, RNA poly 1 Synthesizes rRNA, II synthesizes mRNA, and III synthesizes tRNA. RNA poly. has 5 Subunits: 2 alpha bind regulatory subunits, 1 beta binds the DNA template, 1 beta binds the nucleosides, and one sigma recognizes the promoter and initiates synthesis.

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings RNA polymerase I is responsible for transcribing RNA that becomes structural components of the ribosome. Pol 1 synthesizes a pre-rRNA 45S, whichrRNA matures into 28S, 18S and 5.8S rRNAs which will form the major RNA sections of the ribosome.ribosome RNA polymerase II transcribes protein-encoding genes, or messenger RNAs, which are the RNAs that get translated into proteins. Also, most snRNA (splicing)snRNA and microRNAs (RNAi). This is the most studied type, andmicroRNAs due to the high level of control required over transcription a range of transcription factors aretranscription factors required for its binding to promoters. RNA polymerase III transcribes a different structural region of the ribosome (5s), transfer RNAs, which are also involved the translation process, as well as non-protein encoding RNAs. The enzymes of transcription

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In transcription, the DNA helix unzips –RNA nucleotides line up along one strand of the DNA following the base-pairing rules at the promoter. A regulatory protein binds at -25 binds the TATAAAA box. –This either allows the Polymerase to transcribe or not. Many other protein factors comprise the transcription complex. –50 nucleotides/sec –12 bases in the bubble –No proofreading enzymes like DNA –The single-stranded messenger RNA peels away and the DNA strands rejoin after GC hairpin forming region. RNA polymerase DNA of gene Promoter DNA Terminator DNA Initiation Elongation Termination Area shown in Figure 10.9A Growing RNA RNA polymerase Completed RNA Figure 10.9B

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Noncoding segments called introns are spliced out A cap and a tail are added to the ends 5” cap is a guanosine nucleotide connected to the mRNA via an unusual 5' to 5' triphosphate linkage. This guanosine is methylated on the 7' position directly after capping in vivo by a methyl transferase. The addition of adenine nucleotides (AAA) to the 3′ end of mRNA during posttranscriptional modification Eukaryotic RNA (hnRNA) is processed before leaving the nucleus Figure DNA RNA transcript with cap and tail mRNA ExonIntron Exon Transcription Addition of cap and tail Introns removed Exons spliced together Coding sequence NUCLEUS CYTOPLASM Tail Cap

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Alternative splicing produces multiple messengers

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings In the cytoplasm, a ribosome attaches to the mRNA and translates its message into a polypeptide The process is aided by transfer RNAs Transfer RNA molecules serve as interpreters during translation Figure 10.11A Hydrogen bond Amino acid attachment site RNA polynucleotide chain Anticodon

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Each tRNA molecule has a triplet anticodon on one end and an amino acid attachment site on the other Figure 10.11B, C Anticodon Amino acid attachment site

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Ribosomes build polypeptides Figure 10.12A-C Codons tRNA molecules mRNA Growing polypeptide Large subunit Small subunit mRNA mRNA binding site P siteA site PA Growing polypeptide tRNA Next amino acid to be added to polypeptide

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings An initiation codon marks the start of an mRNA message Figure 10.13A End Start of genetic message

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings mRNA, a specific tRNA, and the ribosome subunits assemble during initiation Figure 10.13B 1 Initiator tRNA mRNA Start codon Small ribosomal subunit 2 P site Large ribosomal subunit A site

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The mRNA moves a codon at a time relative to the ribosome –A tRNA pairs with each codon, adding an amino acid to the growing polypeptide Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure Codon recognition Amino acid Anticodon A site P site Polypeptide 2 Peptide bond formation 3 Translocation New peptide bond mRNA movement mRNA Stop codon

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 1. Initiation

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings The sequence of codons in DNA spells out the primary structure of a polypeptide –Polypeptides form proteins that cells and organisms use Review: The flow of genetic information in the cell is DNA  RNA  protein

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Summary of transcription and translation Figure Stage mRNA is transcribed from a DNA template. Anticodon DNA mRNA RNA polymerase TRANSLATION Enzyme Amino acid tRNA Initiator tRNA Large ribosomal subunit Small ribosomal subunit mRNA Start Codon 2 Stage Each amino acid attaches to its proper tRNA with the help of a specific enzyme and ATP. 3 Stage Initiation of polypeptide synthesis The mRNA, the first tRNA, and the ribosomal subunits come together. TRANSCRIPTION

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure (continued) 4 Stage Elongation Growing polypeptide Codons 5 Stage Termination mRNA New peptide bond forming Stop Codon The ribosome recognizes a stop codon. The poly- peptide is terminated and released. A succession of tRNAs add their amino acids to the polypeptide chain as the mRNA is moved through the ribosome, one codon at a time. Polypeptide

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Mutations are changes in the DNA base sequence –These are caused by errors in DNA replication or by mutagens –The change of a single DNA nucleotide causes sickle-cell disease Mutations can change the meaning of genes

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 10.16A Normal hemoglobin DNA mRNA Normal hemoglobin Glu Mutant hemoglobin DNA mRNA Sickle-cell hemoglobin Val

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Types of mutations Figure 10.16B mRNA NORMAL GENE BASE SUBSTITUTION BASE DELETION ProteinMet Lys PheGlyAla MetLysPheSerAla MetLysLeuAlaHis Missing Missense-mutation causing a change in aa. Nonsense-mutation causing a premature stop codon Causes a “frame shift”

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings BRAC 1 Mutations

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

BRCA 1