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The molecule of heredity Ch 20: Genes and Protein Synthesis DNA Stores the genetic information safely in the nucleus Can be copied and passed from generation to generation Directs the synthesis of proteins Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Watson and Crick’s Discovery of the Double Helix DNA bases pair according to special rules Discovered in 1950 Important because it revealed how DNA can be duplicated from cell to cell And led to the birth of molecular biology There are only 4 kinds of bases (A, T, C, G): A always pairs with T, and C with G Figure 10.5 Close chemical cousins – DNA and RNA Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings What are genes? Both are macromolecules made up of nucleotides Different number of strands 1 base is different In RNA, U substitutes for T Genes The information in DNA is stored in blocks called genes Genes code for proteins; they’re “recipes” for proteins chromosome genetics 101 part 1 What are genes? http://www.youtube.com/watch?v=eOvMNOMRRm8 Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings What happens to chromosomes when a cell divides? DNA Replication DNA replicates by a template mechanism. A copy is made of each chromosome before cell division begins Each daughter cell ends up with a complete set of chromosomes Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Overview of DNA replication 0:48 http://www.youtube.com/watch?v=hfZ8o9D1tus&feature=related Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Copying DNA is a complex process DNA → RNA → Protein Recipe (RNA) “Unzips” the DNA Breaks hydrogen bonds between DNA strands Dish DNA polymerase DNA directs protein synthesis Enzymes needed for DNA replication DNA helicase The DNA molecule ‘unzips’ The parent DNA (blue) serves as a template for making daughter strands (orange) Cook book (DNA) Joins free nucleotides into a new strand of DNA Protein Real-time animation 1:10 http://www.youtube.com/watch?v=4jtmOZaIvS0 Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The flow of genetic information What is the language of DNA? DNA → RNA → Protein DNA carries the directions for an organism. How are these directions carried out? A block of DNA is copied into RNA in the nucleus Transcription The RNA travels to the cytoplasm where it directs the assembly of proteins Just 4 “letters,” A, C, G & T, encode our entire genetic makeup DNA sequence is read in 3letter words or codons Each “word” codes for an amino acid The words are put together into sentences (chains of amino acids or proteins) Translation Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Transcription and translation Information in DNA is transcribed into RNA and then translated into a chain of amino acids. What is the language of DNA and RNA? How do genes code for proteins? The genetic code the order of bases in DNA → the order of amino acids in a protein the sequence of bases Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The genetic code: RNA codons for each amino acid The genetic language is the same in all living things 61 “words” code for amino acids; 3 are stop codons Note: RNA uses the letter “U” instead of “T” Jellyfish make a green fluorescent protein (GFP) Researchers incorporated the gene for GFP into the DNA of a mouse Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Here a mouse expresses a jellyfish gene Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Recap: The flow of genetic information in a cell Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The order of DNA bases the order of mRNA bases How a cell makes protein An Overview the order of the amino acids in the protein Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Copying and delivering the recipe Copying and delivering the recipe The 1st step is to make a copy of the gene Transcription Called mRNA Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The mRNA moves into the cytoplasm Delivers the recipe to a ribosome (the chef) Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Making the protein The ribosome “reads” the sequence of bases Each amino acid called for is connected to the growing chain of amino acids Summary: copying the recipe and making a protein Transcription The mRNA is transcribed in the nucleus. And translated into a chain of amino acids in the cytoplasm. Translation Translation http://www.youtube.com/watch?v=41_Ne5mS2ls&feature=related Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Transcription Copying the gene (transcription) DNA → RNA The gene (DNA) is copied into RNA Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The RNA bases follow the same base-pairing rules that govern DNA replication, except that U pairs with A The RNA bases are linked by the enzyme RNA polymerase (orange blob) Three phases: RNA polymerase attaches to the promoter DNA and starts synthesizing RNA The RNA grows longer RNA polymerase reaches the terminator DNA (stop signal) and detaches Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings An additional twist: not all DNA = protein recipe Parts of DNA do not code for protein RNA splicing: e = exons e i = introns i e i poly-A tail cap e i e (cut-out) e DNA e transcription Removing noncoding regions or introns Splicing exons together Translation: 3 main players i e mRNA AAAAA e e mature mRNA Ribosome mRNA splicing - editing the message 0:39 http://www.youtube.com/watch?v=hV6NSHjTR1s&feature=related Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Fully assembled ribosome Miniature factory for making protein Holds mRNA and 2 tRNA molecules. The growing polypeptide is attached to one of the tRNAs. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Translation: making the chain of amino acids Elongation An incoming tRNA, carrying its amino acid, pairs with the mRNA codon The ribosome catalyzes bond formation between amino acids. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings tRNA (cut-out) Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Translation: getting started 1. 2. 3. An mRNA binds to the small ribosomal subunit. A special initiator tRNA binds to the start codon The large ribosomal subunit binds, creating a functional ribosome. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Translation: signing off Termination Elongation continues until the ribosome reaches a stop codon. The completed protein is freed and the ribosome splits into its subunits. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings The chain of amino acids folds into an active protein The chain of amino acids folds into the elaborate structure that is characteristic of that protein Once it folds, the protein can function Shorthand: The flow of genetic information replication transcription translation DNA → RNA → Protein The central dogma of modern biology For a good review watch Animation of transcription and translation (4:06) http://www.youtube.com/watch?v=41_Ne5mS2ls&feature=related Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Mutations Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings What is a mutation? Any change in the nucleotide sequence of DNA Here a single base is changed: Misspelling Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Mutations: 2 general ways to alter DNA Change a single DNA base Or entire sections of DNA can move from one place to another Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Changes in a single DNA base Caused by errors in DNA replication, UV radiation, or chemical carcinogens Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Changes in a single DNA base Insertions and deletions Can have disastrous effects. Change the reading frame of the gene. Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Mutations are rare Mistakes happen – DNA repair Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings Mutations–key features Mutations are rare changes in DNA can affect genes and the proteins they encode Mutations are inherited only if they occur in germ-line cells Mutations are important for genetic variation and evolutionary change Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings DNA proofreading mechanisms to correct these mistakes The cell uses The daughter strand is compared to the parent DNA to check for mistakes Proofreading is not perfect – mutations are still possible, although rare Copyright © 2007 Pearson Education Inc., publishing as Pearson Benjamin Cummings