Lecture 19 Structure of Nucleic Acids pages 305 310 in Campbell Biology text Be able to describe and interpret the experiment on the replication of the bacterial virus in which it was demonstrated that DNA is the genetic material Know the roles of radioactive sulfur and phosphorus in this experiment Experiment performed by Alfred Hershey and Martha Chase in 1952 Showed that DNA is the genetic material of a phage known as a T2 They already knew that the phage T2 was composed almost entirely of DNA and protein and could quickly turn an E coli cell into a T2 producing factory that released many copies when cell ruptured Question experiment answerd T2 can reprogram its host cell to produce viruses but which viral component protein or DNA is responsible Used radioactive isotope of sulfur to tag protein in one batch of t2 and a radioactive isotope of phosphorus to tage DNA in second batch It was found that the phage DNA entered host cells but phage protein didn t further showing DNA played an ongoing role Know the components of a nucleotide and how nucleotides are joined together to make nucleic acids phosphodiester bonds are formed between the 5 carbon on sugar of one nucleotide with 3 carbon on the sugar of the next nucleotide know how the 5 and 3 ends of a nucleic acid differ Components of a nucleotide Nitrogenous base pentose sugar called deoxyribose and a Bases can be Adenine Thymine Guanine or Cytosine Adenine pairs with Thymine Guanine Direction goes from 5 to 3 adding only to 3 end these numbers refer to the numbers assigned phosphate group pairs with Cytosine to the carbons in the sugar ring Be able to state the names of the nucleic acid bases and know the chemical composition of DNA and RNA Bases can be Adenine Thymine Guanine or Cytosine Adenine pairs with Thymine Guanine pairs with Cytosine RNA uses Uracil instead of Thymine Be able to describe the Watson and Crick model for the structure of DNA double stranded antiparallel helix X rays showed helical in shape Determined helix was made of two strands double helix Sugar phophate backbones on outside of DNA model Two sugar phosphate backbones anti parallel Lecture 20 DNA Replication pages 311 317 in Campbell Biology text Be able to explain the difference between conservative semiconservative and dispersive replication Conservative Two parental strands reassociate after acting as templates for new strands thus restoring the parental double helix Semiconservative Two strands of parental molecule separate and each functions as a template for synthesis of a new complementary strand Dispersive Each strand of both daughter molecules contains a mixture of old and newly synthesized DNA Be able to outline the Messelson Stahl experiment in which it was demonstrated that DNA replication was semiconservative and interpret the results understand what results would have been expected if replication was conservative or dispersive They cultured E coli for several generations in a medium containing nucleotide precursors labeled with heavy nitrogen isotope then transferring bacteria to a medium with lighter nitrogen isotope Samples taken after first and second replication Extracted dna from bacteria then centrifuged to separate dna of different densities Compared their results to those predicted by each of the three models First replication produced a band of hybrid DNA eliminating conservative Second replication produced both light and hybrid DNA which supported semiconservative model That DNA polymerase requires a DNA template a primer synthesizes 5 to 3 and uses deoxynucleotide triphosphates understand what 5 3 synthesis means the polymerase adds a nucleotide to the hydroxyl on the 3 end of the growing nucleotide chain This means that DNA polymerases can only add nucleotides to the free 3 end of a primer or growing DNa strand never to 5 end Know that DNA replication begins at sites called origins and proceeds bidirectionally away from the origin This produces two replication forks that move away from the origin and both strands of DNA are replicated simultaneously at each fork Know what the leading strand and the lagging strand are Leading strand The new complementary DNA strand synthesized continuously along the template strand towards the replication fork in the mandatory 5 to 3 direction Lagging strand A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments each synthesized in 5 to 3 direction away from replication fork Know the roles of the following enzymes in DNA replication Helicase Primase DNA polymerase III and DNA polymerase I Helicase Enzymes that untwist the double helix at replication forks separating the two parental strands and making them available as template strands Primase starts a complementary RNA chain from a single RNA nucleotide adding RNA nucleotides one at a time using parental DNA strand as template DNA polymerase 3 Adds a nucleotide to the RNA primer and then continues adding DNA nucleotides complementary t parental DNA template strand to growing ends of new DNA strand DNA polymerase 1 Replaces RNA nucleotides of adjacent primer with DNA nucleotides Know the importance of DNA repair and be able to explain how it works repair enzymes identify unpaired bases or damaged bases and cut them out from one side of the double helix then DNA polymerase I fills in the correct bases used complementary base pairing with the DNAs undamaged strand He explains in the question above Know what a thymine dimer is and what causes it to form Covalent linking of thymine bases that are adjacent on DNA strand Cause DNA to buckle and interfere with DNA replication Lecture 21 Transcription pages 326 328 332 335 in Campbell Biology text Understand the difference between transcription and translation Transcription Synthesis of RNA using a DNA template Translation Synthesis of a polypeptide using the genetic information encoded in an mRNA molecule Know that a gene is a stretch of bases in DNA that is transcribed into an RNA product Each polypeptide is coded for by a single gene Know that genes that code for polypeptides are transcribed into a mRNA and know some genes code for RNA molecules that are not translated rRNAs and tRNAs An RNA polymerase converts the info in DNA into single stranded RNA requries a DNA template synthesizes 5 to 3 using ribonucleotide triphosphates but does not need a primer Know what the promoter is where it is found Promoter is the DNA sequence where RNA polymerase attaches and
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