Bio11 Announcements TODAY Genetics (review) and quiz (CP #4) Structure and function of DNA Extra credit due today Next week in lab: Case study presentations Following week: Lab Quiz 2 Ch 21: DNA Biology and Technology DNA Functions DNA Stores genetic information Can be copied and passed from generation to generation Directs the synthesis of proteins What are genes? The information in DNA is stored in blocks called genes Genes code for proteins; they re recipes for proteins DNA stores the genetic information safely in the nucleus genetics 101 part 1 What are genes? http://www.youtube.com/watch?v=eovmnomrrm8 DNA and RNA Structure DNA and RNA are nucleic acids. They are polymers of nucleotides. The nucleotides are joined by a sugar-phosphate backbone. How do DNA and RNA differ? Nitrogenous bases DNA C G A T RNA C G A U Sugar Deoxyribose Ribose Number of strands 2 1
Watson and Crick s Discovery of the Double Helix James Watson and Francis Crick determined that DNA is a double helix in 1950. DNA structure a helix Watson and Crick used X-ray crystallography data to reveal the basic shape of DNA. Rosalind Franklin collected the X-ray crystallography data. DNA structure a double helix Replication: copying DNA strands The model of a double helix a rope ladder twisted into a spiral. Each rung stands for a pair of bases connected by hydrogen bonds DNA Replication When a cell divides, it ensures that daughter cells carry the same genetic information DNA replicates by a template mechanism. The DNA molecule unzips The parent DNA (blue) serves as a template for making daughter strands (orange) DNA replication DNA polymerase binds to specific sites on the double helix. Proceeds in both directions shortens the time needed for DNA replication. Overview of DNA replication 0:48 http://www.youtube.com/watch?v=hfz8o9d1tus&feature=related http://www.youtube.com/watch?v=4jtmozaivs0
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 flow of genetic information DNA RNA Protein The RNA travels to the cytoplasm where it directs the assembly of proteins Translation From Nucleotides to Amino Acids: An Overview Genetic information in DNA is transcribed into RNA and then translated into polypeptides. What is the language of DNA and RNA? the sequence of bases Transcription and translation RNA is then translated into a sequence of amino acids RNA is divided into codons (3 RNA bases) Each codon specifies an amino acid How do genes code for proteins? The genetic code the rules for translating the order of bases in DNA into the order of amino acids in a protein Codon: 3 bases that code for an amino acid The genetic code The RNA codons for each amino acid The genetic code is shared by all organisms Here a mouse expresses a jellyfish gene Researchers incorporated the gene for GFP from a jellyfish into the DNA of a mouse
Transcription: From DNA to RNA Transcription DNA RNA. An RNA molecule is copied from a DNA template. The RNA nucleotides follow the same base-pairing rules that govern DNA replication, except that U pairs with A The RNA nucleotides are linked by the enzyme RNA polymerase (orange blob) Transcription of a gene Three phases: Initiation RNA polymerase attaches to the promoter and starts synthesizing RNA Elongation The RNA grows longer Termination RNA polymerase reaches the terminator DNA (stop signal) and detaches RNA is processed in eukaryotes RNA processing includes: Adding a cap and tail Removing introns Internal noncoding regions Splicing exons together The messenger RNA (mrna) travels to the cytoplasm Translation: The Players Translation: RNA protein Three main players: Messenger RNA (mrna) Transfer RNA (trna) Ribosomes What do they do? Tranlate the genetic code from the nucleic acid language to the protein language.
Messenger RNA (mrna) Transfer RNA (trna) mrna the copy of the DNA that codes for a protein Is the first ingredient for translation. trna Acts as a interpreter Carries amino acids. Matches amino acids with codons in mrna using anticodons. Ribosomes Fully assembled ribosome Ribosomes Are organelles that actually make the proteins. Made of ribosomal RNA (rrna) and protein 2 subunits Binding sites for trna and mrna A fully assembled ribosome holds 2 trna molecules and mrna. The growing polypeptide is attached to one of the trnas. Translation: The Process Translation is divided into three phases: Initiation Elongation Termination Initiation The first phase brings the players together: The mrna The first amino acid with its attached trna The two subunits of the ribosome An mrna molecule has a cap and tail that help it bind to the ribosome.
The initiation of translation 1. An mrna binds to the small ribosomal subunit. 2. Then a special initiator trna binds to the start codon, AUG 3. The large ribosomal subunit binds, creating a functional ribosome. The initiator trna fits into the P site on the ribosome. The process of Elongation Step 1, codon recognition The anticodon of an incoming trna, carrying its amino acid, pairs with the mrna codon in the A site. Elongation Elongation Step 2, peptide bond formation The ribosome catalyzes bond formation between amino acids. Step 3, translocation A trna leaves the P site of the ribosome. The ribosome moves the remaining trna to the P site. The trna and mrna move as a unit. The process begins again with step 1. Termination Elongation continues until the ribosome reaches a stop codon. The completed polypeptide is freed and the ribosome splits into its subunits. A summary of transcription and translation In eukaryotic cells, Transcription occurs in the nucleus. Translation occurs in the cytoplasm.
Recap: The flow of genetic information in a cell Mutations The order of DNA bases the order of mrna bases the order of the amino acids in the protein Mutations A mutation is any change in the nucleotide sequence of DNA. A small change can make a BIG difference Normal Hb Mutant Hb A change in a single nucleotide in the gene for hemoglobin A change in a single amino acid A change in the shape of the protein and RBC and causes DISEASE Mutations 2 general ways to alter DNA A change in a single DNA base Result from errors in DNA replication, UV radiation, or chemical mutagens Or entire sections of DNA can move from one place to another Recombination Mutations in a single DNA base Two categories: 1. Base substitutions 2. Base insertions or deletions
Mutations Mistakes happen DNA repair Because so much DNA is being replicated in the many cells of the body, mistakes occur The cell has many mechanisms to correct these mistakes called DNA repair or proofreading mechanisms The proofreading process involves comparing the daughter strand to the parent DNA to check for mistakes the proofreading is not perfect mutations are still possible, although rare Mutations in DNA repair genes cause cancer DNA repair or proofreading genes help the cell to fix mutations in its DNA. When a DNA repair gene is mutated, the cell can t repair mistakes in its DNA. These mistakes build up until an oncogene is hit. Then the cell becomes cancerous. 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