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MSU ISB 202 - Lecture 5: Nucleic Acids into Protein
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Lecture 5: Nucleic Acids into Protein. (Ch 12 and 13)Introduction to Nucleic AcidsMystery of the Hereditary MaterialStructure of the Hereditary MaterialHershey-Chase ExperimentBacteriophagesHershey & Chase’s ExperimentsHershey and Chase ResultsSlide 9Radical New View of Life!Structure of Nucleotides in DNANucleotide BasesComposition of DNARosalind Franklin’s WorkPowerPoint PresentationWatson-Crick ModelSlide 17DNA Structure Helps Explain How it DuplicatesDNA ReplicationBase Pairing During ReplicationEnzymes in ReplicationA Closer Look at Strand AssemblyContinuous and Discontinuous AssemblyDNA RepairCloningDolly: Cloned from an Adult CellMore ClonesSlide 28Nucleic Acids Into ProteinsSteps from DNA to ProteinsThree Classes of RNAsDNA vs. RNABase Pairing During TranscriptionTranscription & DNA ReplicationPromoterGene TranscriptionAdding NucleotidesTranscript ModificationGenetic CodeCode Is RedundantRedundant? (Genetic Code Secret Decoder Ring)Three Stages of TranslationKey Players in TranslationRibosomesBinding Sites on Large SubunittRNA StructureInitiationElongationSlide 49TerminationPolysomeWhat Happens to the New Polypeptides?OverviewWhen Things Go WrongEffect of Base-Pair SubstitutionFrameshift MutationsMutation RatesLecture 5: Nucleic Acids into Protein. (Ch 12 and 13)Goals–Introduction to nucleic acids, DNA and replication–Understand how to make a protein (transcription)Key Terms: DNA, RNA, nucleic acid, replication, polymerase, ligase, transcription, translation, ribosome, splicing, mRNA, tRNA,Introduction to Nucleic AcidsMystery of the Hereditary Material•Originally believed to be an unknown class of proteins•Thinking was–Heritable traits are diverse–Molecules encoding traits must be diverse–Proteins are made of 20 amino acids and are structurally diverseStructure of the Hereditary Material•Experiments in the 1950s showed that DNA is the hereditary material•Scientists raced to determine the structure of DNA•1953 - Watson and Crick proposed that DNA is a double helixHershey-Chase Experiment•1917, Discovery of Bacteriophage–Why doesn’t everyone die of bacterial dysentary?–What’s eating the bacteria?•The MSU story–1950, Harold Sadoff U of Ill: Micro aerosols–1952, Hershey and Chase ExperimentBacteriophageBacteriophages•Viruses that infect bacteria•Consist of protein and DNA•Inject their hereditary material into bacteriacytoplasmbacterial cell wallplasma membraneHershey & Chase’s Experiments•Created labeled bacteriophages–Radioactive sulfur –Radioactive phosphorus •Allowed labeled viruses to infect bacteria•Asked: Where are the radioactive labels after infection?virus particle labeled with 35Svirus particle labeled with 32Pbacterial cell (cutaway view)label outside celllabel inside cellHershey and Chase Results1. Label protein or DNA with radio isotopes2. Infect bacteria with phage particles3. Sheer off the phage (blender)4. Separate bacteria and phage protein5. Progeny of the phageHershey and Chase Results•Conclusions:–DNA is the infective material not protein–Strong inference: DNA is genetic informationRadical New View of Life!Sickle Cell Anemia, A Molecular Disease, Pauling et al. Science 1949Structure of Nucleotides in DNA•Each nucleotide consists of–Deoxyribose (5-carbon sugar) –Phosphate group–A nitrogen-containing base•Four bases–Adenine, Guanine, Thymine, CytosineNucleotide Basesphosphate groupdeoxyribose ADENINE (A) THYMINE (T)CYTOSINE (C)GUANINE (G)Composition of DNA•Chargaff showed:–Amount of adenine relative to guanine differs among species–Amount of adenine always equals amount of thymine and amount of guanine always equals amount of cytosineA=T and G=CRosalind Franklin’s Work•Was an expert in x-ray crystallography•Used this technique to examine DNA fibers •Concluded that DNA was some sort of helix•DNA is a very long molecule and does not naturally form long, thin fibres. But it is possible to extract DNA from cells in the form of a viscous gel; if a needle is dipped into the gel and slowly wound up, it drags out a DNA fibre in which many molecules are lined up parallel to each other. The X-ray patterns given by DNA fibres show a pair of strong arcs along their vertical axis; Astbury realised that their position indicated a very regular periodicity of 3.4 along the axis of the fibre and that this figure was similar to the thickness of the DNA bases; he therefore suggested that the bases were stacked on top of each other "like a pile of pennies". He was quite right, but the well-known double helix structure had to await much better X-ray pictures (obtained by Wilkins, Franklin and colleagues at King's College, London) and the realisation by Crick and Watson (in Cambridge) that the bases were in pairs, joining two backbones running in opposite directions.Watson-Crick Model•DNA consists of two nucleotide strands•Strands run in opposite directions•Strands are held together by hydrogen bonds between bases•A binds with T and C with G•Molecule is a double helixWatson-Crick ModelHydrogen BondsHydrogen BondsCovalent BondsCovalent BondsDNA Structure Helps Explain How it Duplicates•DNA is two nucleotide strands held together by hydrogen bonds•Hydrogen bonds between two strands are easily broken•Each single strand then serves as template for new strandDNA Replicationnewnew old old•Each parent strand remains intact•Every DNA molecule is half “old” and half “new”Base Pairing During ReplicationEach old strand serves as the template for complementary new strandEnzymes in Replication•Enzymes unwind the two strands•DNA polymerase attaches complementary nucleotides •DNA ligase fills in gaps •Enzymes wind two strands togetherA Closer Look at Strand AssemblyEnergy for strand assembly is provided by removal of two phosphate groups from free nucleotidesnewlyformingDNAstrandone parent DNA strandContinuous and Discontinuous AssemblyStrands can only be assembled in the 5’ to 3’ directionDNA Repair•Mistakes can occur during replication•DNA polymerase can read correct sequence from complementary strand and, together with DNA ligase, can repair mistakes in incorrect strand•DNA damage from environmental factorsCloning•Making a genetically identical copy of an individual•Is cloning new?–Natural Clones- Maternal twins–Synthetic Clones-•Researchers have been creating clones for decades•Clones were created by embryo


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