BCHM 3050 1ST Edition Lecture 15 Outline of Last Lecture I Levels of Structure in DNA II Formation of Phosphodiester Bonds III B DNA Spatial Dimensions IV Stabilizing Forces in DNA V Functions of Major Grooves VI Functions of Minor Grooves VII DNA Structural Variations Outline of Current Lecture I Super Coiling of DNA II Packaging of Eukaryotic DNA III RNA vs DNA IV Types of RNA V Transfer RNA VI Ribosomal RNA VII Griffith s Experiment VIII Avery MacLeod McCarty Experiment IX Griffith and Avery s Experiment X Hershey and Chase Experiment Current Lecture These 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 I Super Coiling of DNA a A and T have a double bond between them b G and C have a triple bond between them c No two people have the same sequence of bases except identical twins d DNA undergoes changes over time epigenetics e DNA has to be supercoiled in order to fit in such a compact space f Supercoiling makes it inaccessible which is a way the cell protects the DNA from mutagens g Supercoiling makes sure that the replication factors needed for the DNA replication process access the DNA only at specific times h Higher organisms have maximum supercoiling II Packaging of Eukaryotic DNA a The dots on the print out are groups of proteins called histones that sit on the DNA b Nucleosome group of 8 histone proteins that bind to the DNA at certain intervals c When cell is splitting DNA is at its maximum supercoiling tightly packed and not accessible to anything else d Heterochromatin i Nucleosome are so tightly packed that there is no DNA between ii highly supercoiled state cannot participate in anything e Euchromatin i Certain enzyme push the histones apart and expose DNA between ii less super coiling beads in a string state when replication and other processes occur iii DNA is exposed and can get attacked by other molecules f 140 base pairs of DNA rapped around nucleosome g Linker DNA 60 base pairs h 140 more base pairs i H1 does not have a role in the part of the nucleosome j Overall charge of DNA is negative which means the histone proteins have to be positively charged basic amino acids especially arginines and lysines that get chemically k Modifying the arginines and lysines in histones changed it from heterochromatin to euchromatin III RNA vs DNA a RNA is much more abundant than DNA because there are many more copies of RNA s messages transfer species ribosome numbers made than the 2 copies of DNA b Modified bases in tRNA include pseudouridine dihydrouridine 4 thiouridine 1 2 methylguanosines especially in loops c U is replaced by T i e methylated uracil because T will only base pair with A U however is the only base that can base pair with any of the other bases Evolutionarily this could not be tolerated to maintain the fidelity required in DNA base pairing d RNA is more transient and more easily degraded e Secondary structure of RNA i Single strand of RNA is very flimsy ii Can make transient bonds with its own strand IV Types of RNA a snRNA s thought to complex with proteins to form snRNPs small nuclear ribonucleo proteins are involved in removing introns and then splicing exons together to form functional mRNA s b snoRNA s small nucleolar snoRNA small nucleolar RNA forms snoRNPs which process rRNA mostly by methylation and isomerisation thought to be involved in ribosome biogenesis c siRNA small interfering RNA involved in gene silencing and regulation d gRNA guide RNA needed for RNA editing the removal and insertion of bases into mRNA e tmRNA an RNA molecule that disengages ribosomes from stalled translation of mRNA in bacteria f telomerase RNA an RNA molecule that forms much of the structure and all of the template required by telomerase g hnRNA rag bag of unprocessed pre mRNA transcripts and other heterogeneous nuclear RNAs of less well defined function h tRNA and mRNA involve in translation i V snRNA involved in splicing Transfer RNA a tRNA stays in the clover leave position because of the modifications of uracil and guanine b Know the names of the modifications of uracil and guanine found in tRNA c Amino acid can only attack to the tRNA at the 3 end anticodon end d tRNA participates in translation e All tRNAs have CCA followed by an amino acid at the 3 end f VI Each amino acid has its own special tRNA Ribosomal RNA a rRNA lives in the ribosome b Very rigid and assume a specific structure c rRNA sits on the ribosome in this specific conformation in all organisms d rRNA plays important role in translation and protein synthesis VII Griffith s Experiment a Isolated 2 different strains of the bacteria R and S b R rough strain is devoid of capsule which is what infects this is avirulent and allowed the mice to live c S smooth strain with capsule virulent and kills mice d Experiment e heat kills the S strain and infected the mouse mouse lived so heat can destroy whatever is making this bacteria infectious f Combined R strain and the heat killed S strain and injected into mouse mouse died strain of virulent g Conclusion somehow the R strain was transformed in the presence of heat killed S strain to make it virulent h Some unknown particle is a transforming agent which we know today is DNA i VIII R bacteria heat killed S virulent R strain Avery MacLeod McCarty Experiment a Knew we could isolated DNA protein carbohydrates lipids b Avery MacLeod McCarty hypothesized that one of these 4 molecules was the transforming agent c Amylase kills all carbohydrates heat killed S and R combo still killed mice and transferred R d Protease kills proteins still transformed R e Dnase degraded DNA heat killed S could not transform R so this shows that the DNA is the transforming agent f RNase degraded RNA transformed R g DNA could also transform over generations and between one species and another IX Griffith and Avery s Experiment a Non virulent strain injected in mice live b Virulent strain injected in mice die c Heat killed virulent strain injected in mice live d Heat killed virulent strain and non virulent strain injected in mice die X Hershey and Chase Experiment a Proved that DNA is a genetic material b They used a virus and bacteria c Virus injects something inside of the host cell reconstitute into a new virus inside the cell d Cover of the virus is the protein green and red is the DNA which is the infectious agent e Elements present in DNA phosphorus nitrogen carbon oxygen f Elements in
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