BIOL 1181st Edition Lecture 14 Outline of Last Lecture I. DNA’s Primary StructureII. DNA Has DirectionalityIII. DNA’s Secondary StructureIV. DNA Strands Are Templates for DNA SynthesisV. How Do the New DNA Strands Form?VI. A Comprehensive Model for DNA SynthesisVII. Characteristics of DNA PolymerasesVIII. How Does Replication Get Started?IX. How is the Helix Opened & Stabilized?X. How is the Leading Strand Synthesized?XI. PrimaseXII. The Lagging StrandXIII. How is the Lagging Strand Synthesized?XIV. The Discontinuous Replication HypothesisXV. The Discovery of Okazaki FragmentsXVI. DNA Synthesis Enzymes Are Well-OrganizedXVII. Replicating the Ends of Linear ChromosomesXVIII. Repairing Mistakes & DNA DamageThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.XIX. If DNA is Damaged, How is It Detected?XX. What if DNA Polymerase Misses an Error?XXI. Repairing Damaged DNAXXII. Nucleoside Excision Repair SystemOutline of Current Lecture I. IntroductionII. Gene ExpressionIII. What Do Genes Do?IV. The One-Gene, One-Enzyme HypothesisV. The Central Dogma of Molecular BiologyVI. RNA- The Intermediary Between Genes and ProteinsVII. The Central DogmaVIII. The Roles of Transcription and TranslationIX. Exceptions to the Central DogmaX. The Genetic CodeXI. How Long Is A Word in the Genetic Code?XII. What is a Codon?XIII. Cracking the Genetic CodeXIV. Important Properties of the CodeXV. Using the CodeXVI. What is the Molecular Basis of Mutation?XVII. Mutations Have Varying Effects on OrganismsXVIII. Chromosome MutationsCurrent LectureIntroduction- The work of early geneticists illuminated the structure of DNA & genes- The method of inheritance including Mendel, Watson & Crick & others- Biologists still did not understand how gene expression occurredGene Expression- The process of translating the information in DNA into functioning molecules within the cellWhat Do Genes Do?- George Beadle & Edward Tatum proposed that genes carry the instructions for making and maintaining an individual- how?o Damage a gene by creating a mutant o Then observe the resulting effect on the mutant’s phenotypeo Nonfunctioning alleles are now called knock-out null or loss-of-function allelesThe One-Gene, One-Enzyme Hypothesis- To test hypothesis: Beadle & Tatum damaged genes in the bread mold Neurospora crassa- Observed that defects in particular genes resulted in the mold’s inability to produce specific proteins- The results of their experiments inspired their one-gene, one-enzyme hypothesis- Proposed that each gene contains the information needed to make an enzymeThe Central Dogma of Molecular Biology- Francis Crick: proposed DNA is an information storage molecule- Sequence of bases in DNA is a code different combinations of bases specify the 20 amino acids- Gene: a particular stretch of DNA that contains the information to specify the amino acidsequence of one proteino Information encoded in the base sequence of DNA is not directly translated into the amino acid sequence of proteins- Central Dogma: DNA converted to RNA (transcription) & RNA in converted to protein (amino acid sequence; translation)RNA- The Intermediary Between Genes and Proteins- Francois Jacob & Jacques Monod proposed 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 DNAThe Central Dogma- The central dogma summarizes the flow of information in cells- DNA codes for RNA, which codes for proteins: DNA RNA Proteins- The sequence of bases in a stretch of DNA specifies the sequence of bases in an RNA molecule, which in turn, specifies the sequence of amino acids in a protein- Genes ultimately code for proteinsThe Roles of Transcription & Translation- DNA is transcribed to mRNA by RNA polymerase- Transcription: the process by which the hereditary information in DNA is copied to RNA- mRNA is then translated to protein- Translation: the process where the order of the nucleotide bases is converted to the order of amino acids- DNA (info storage)TranscriptionmRNA (information carrier)TranslationProteins (active cell machinery)- According to central dogma, an organism’s genotype is determined by the sequence of bases in its DNA- Phenotype is a product of the proteins it produces- Alleles of the same gene differ in their DNA sequence- Proteins produced by different alleles of the same gene frequently differ in their amino acid sequenceExceptions to the Central Dogma- Many genes code for RNA molecules that do not function as mRNAs are not translated into proteins- These other RNAs perform important functions in the cell- Sometimes information flows in the opposite direction, from RNA back to DNA- Ex. Some viral genes are composed of RNA use reverse transcriptase, a viral polymerase, to synthesize a DNA version of the virus’s RNA genesThe Genetic Code - How does the sequence of bases in a strand of mRNA code for the sequence of amino acids in a protein?- The genetic code contains the rules that specify the relationship between a sequence of nucleotide bases in DNA or RNA- The corresponding sequence of amino acids in a proteinHow Long Is a Word In the Genetic Code- George Gamow predicted each word in the genetic code contains 3 bases - There are 20 amino acids but only 4 RNA bases- A 3 base code is the least that could specify enough amino acids could code for 64 amino acids- 3 base code provides more than enough messages to code for all 20 amino acids- 3 base code= triplet codeWhat is a codon?- The group of 3 bases specifies a particular amino acid- Francis Crick & Sydney Brenner found that the reading frame (sequence of codons) of a gene could be destroyed by mutation and then restored if the total number of deletion or additions were multiples of 3Cracking the Genetic Code- There is one start codon (AUG) signifies the starts of the protein-encoding sequence inmRNA- There are 3 stop codons (UGA, UAA & UAG) in the genetic code signal the end of the protein coding sequenceImportant Properties of the Code- It is redundanto All amino acids except 2 are encoded by more than one codon- It is ambiguouso One
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