15. How genes work? Key ConceptsPowerPoint PresentationSlide 3Slide 4The Central Dogma of Molecular BiologyRNA—the Intermediary between Genes and ProteinsThe Central DogmaThe Roles of Transcription and TranslationVisualizing the Central DogmaBiologists use the terms transcription and translation to describe the two steps in genetic information flow from DNA to protein. Which of the following is correct?Exceptions to the Central DogmaThe Genetic CodeHow Long Is a Word in the Genetic Code?Slide 14Slide 15How Did Researchers Crack the Code?Slide 17Important Properties of the CodeUsing the CodeSlide 20Early in the evolution of life on Earth, there may have been fewer than 20 amino acids and fewer than 4 mRNA bases. If “primitive proteins” were composed of only 14 different kinds of amino acids and “primitive mRNAs” contained only 2 bases, what would be the fewest number of bases that could code for the 14 different amino acids?How genes work?What Is the Molecular Basis of Mutation?Point MutationsSlide 25Slide 26Slide 27Mutations Have Varying Effects on Organisms© 2011 Pearson Education, Inc.15. How genes work? Key ConceptsMost genes code for proteins.DNA is transcribed to messenger RNA by RNA polymerase, and then messenger RNA is translated to proteins by ribosomes. In this way, genetic information is converted from DNA to RNA to proteins.Each amino acid in a protein is specified by a group of three bases in messenger RNA.Mutations are random changes in DNA, ranging in extent from single bases to large chromosome regions, that may or may not produce changes in the phenotype.consists offunctional units calledis archived inbase sequences ofDNA4.2GENETIC INFORMATIONGenesEXPRESSED15.115.217.1–418.1–4Text sectionwhere youcan find moreinformation13.2Genotypeis packaged withproteins to formhave differentversions calledmake upcan bemay regulatewhether genesif firstTRANSCRIBED byRNA polymerase16.14.3to formRNAmay beprocessed bymay functiondirectly incell as16.2• Splicing• Addition of 5 cap• Addition of poly(A) tailto form16.416.5• tRNA (transfer RNA)• rRNA (ribosomal RNA)mRNA(messenger of RNA)16.2is thenTRANSLATED byaffectRibosomes16.5to formProteins3.216.5changed byproduce13.1Phenotype• Folding• Glycosylation• Phosphorylation• Degradation3.45.39.118.4Chromatin18.2COPIED14.313.2AllelesarebyDNA polymerase14.3occasionallymake errors,causingMUTATION15.4Chromosomes11.118.2andcan becan bemay change due tocausing• Breakage• Duplication or deletion due to errors in meiosis• Damage by radiation or other agents14.515.412.415.4Mutationcan beto somaticcells byto germ cells by12.1, 13.1–4TRANSMITTED11.111.1MITOSIS12.1MEIOSISincludes12.2 13.3–4• Independent assortment• Recombinationstarts with starts withParent cell2n 2nParent cellends with ends with2n 2nTwo daughter cellswith the same geneticinformation as theparent cell (unlessmutation has occurred).Four daughter cellswith half the geneticinformation as theparent cell.nnnnoccursduringoccursduringGROWTH and ASEXUALREPRODUCTIONSEXUALREPRODUCTION11.0 12.3result in results inLow genetic diversity High genetic diversityis archived inbase sequences ofDNAGENETIC INFORMATIONGenesEXPRESSEDText sectionwhere youcan find moreinformationconsists offunctional units called13.2Genotypemake upcan bemay regulatewhether genesif firstTRANSCRIBED byRNA polymerase16.14.3to formRNA4.215.115.217.1–418.1–44.3RNAmay beprocessed bymay functiondirectly incell as16.2• Splicing• Addition of 5 cap• Addition of poly(A) tailto form16.416.5• tRNA (transfer RNA)• rRNA (ribosomal RNA)mRNA(messeger of RNA)16.2is thenTRANSLATED byaffectRibosomes16.5to formProteins3.216.5changed byproduce13.1Phenotype• Folding• Glycosylation• Phosphorylation• Degradation3.45.39.118.4© 2011 Pearson Education, Inc.The Central Dogma of Molecular Biology•Francis Crick proposed that DNA is an information storage molecule, and that the sequence of bases in DNA is a kind of code in which different combinations of bases could specify the 20 amino acids.•A particular stretch of DNA (a gene) contains the information to specify the amino acid sequence of one protein.•The information encoded in the base sequence of DNA is not directly translated into the amino acid sequence of proteins.© 2011 Pearson Education, Inc.RNA—the Intermediary between Genes and Proteins•François Jacob and Jacques Monod proposed that RNA molecules act as a link between genes, found in the cell’s nucleus, and the protein-manufacturing centers, located in the cytoplasm. •Messenger RNA (mRNA) was found to carry information from DNA to the site of protein synthesis.•The enzyme RNA polymerase synthesizes RNA according to the information provided by the sequence of bases in a particular stretch of DNA.© 2011 Pearson Education, Inc.The Central DogmaThe sequence of bases in a particular stretch of DNA specifies the sequence of bases in an RNA molecule, which specifies the sequence of amino acids in a protein. In this way, genes ultimately code for proteins.The central dogma summarizes the flow of information in cells. It states that DNA codes for RNA, which codes for proteins: DNA  RNA  proteins© 2011 Pearson Education, Inc.The Roles of Transcription and Translation•DNA is transcribed to messenger RNA by RNA polymerase. –Transcription is the process by which the hereditary information in DNA is copied to RNA.•The mRNA is then translated to protein.–Translation is the process wherein the language of nucleic acids, the order of the nucleotide bases, is converted to the language of proteins, the order of amino acids.© 2011 Pearson Education, Inc.Visualizing the Central DogmaDNA(information storage)TranscriptionmRNA(information carrier)TranslationProteins (active cell machinery)According to the central dogma, an organism’s genotype is determined by the sequence of bases in its DNA, while its phenotype is a product of the proteins it produces.© 2011 Pearson Education, Inc.Biologists use the terms transcripti on and translation to describe the two steps in genetic information flow from DNA to protein. Which of the following is correct? a. Transcription is the synthesis of protein from mRNA by ribosomes; translation is the synthesis of mRNA from DNA by RNA polymerase.b. Transcription is the synthesis of mRNA from DNA by ribosomes; translation is the synthesis of protein from mRNA by RNA polymerase.c.