BISC 330L Biochemistry Spring 2015 USC Lecture 11 Friday Feb 6 2015 Chapter 4 Flow of Genetic Information Review RNA DNA structure Watson Crick proposal Chapter 4 DNA RNA and the Flow of Genetic Information DNA RNA PROTEIN The Watson Crick Proposal DNA composed of two chains Two chains spiral around each other Sugar phosphate backbone on the outside Bases situated inside double helix perpendicular to long axis Major and minor grooves One turn of helix 10 nucleotides Two chains are complementary and antiparallel H bonds between bases Pyrimidines always pair with purines Erwin Chargaff showed that base composition varies from organism to organism A T C G Organism E coli Human Mycobacterium 15 15 35 35 40 40 10 10 30 30 20 20 Chargaff s Rules A T and G C BUT A T did NOT equal the G C Chargaff s Rules and base pairing X ray diffraction of DNA Maurice Wilkins and Rosalind Franklin Importance of Watson Crick Model Determining the structure had TWO important outcomes 1 Gave rise to obvious and testable hypotheses about how genetic information could be stored and duplicated 2 Gave rise to the starting point for the development of techniques to study DNA The General Structure of the Nucleic acids Information unique and sequence dependent Scaffold common and sequence independent Ribose vs Deoxyribose RNA DNA Backbones of DNA and RNA The Bases DNA bases 2 purines A G and 2 pyrimidines C T RNA bases 2 purines A G and 2 pyrimidines C U Note T 5 methyl U so C T requires two chemical changes deamination methylation whereas C U only requires one deamination Nucleic Acid Terminology Base Sugar nucleoside Adenosine Deoxyadenosine Guanosine Deoxyguanosine Cytidine Deoxycytidine Uridine Thymidine Base Sugar Phosphate Group Nucleoside 5 phosphate 5 nucleotide The Structure of ATP Adenosine 5 TriPhosphate High energy bonds Chemical structure of Guanosine 5 TriPhosphate GTP GTP 1 2 3 4 5 3 5 3 5 3 5 phosphodiester bond Covalent structure of polynucleotide chain DNA chain is more stable more inert than RNA chain because it has 2 H instead of 2 OH The 2 OH in RNA promotes hydrolysis of the 3 5 phosphodiester linkage Polarity of a DNA Strand DNA is composed of a sugar phosphate backbone Dissecting the Double Helix Hydrophobic stacking Phosphodiester bond Hydrogen bonding Base stacking axial view Three Forms of DNA DNA Right handed One turn 2 53 nm Distance between bp 0 23 nm There are 11 bp turn Right handed One turn 3 4 nm Distance between bp 0 34 nm There are 10 bp turn Left handed One turn 4 56 nm Distance between bp 0 38 nm There are 12 bp turn Nucleic Acids and Absorbance The DNA double helix has a Melting Temperature Tm dependent on salt concentration Below Tm Above Tm Above Tm the two complementary strands dissociate melt Below Tm the two strands spontaneously reassemble to form the double helix Nucleic Acid Absorbance vs Temperature What about single stranded nucleic acids Can fold into stem loop structures Complex Folding of RNA Can RNA perform an enzymatic function Ribozymes Hammerhead ribozyme RNase P Group I and Group II introns GIR1 branching ribozyme HDV ribozyme Mammalian CPEB3 ribozyme VS ribozyme glmS ribozyme CoTC ribozyme Peptidyl transferase 23S rRNA Leadzyme Hairpin ribozyme Hammerhead Ribozyme Catalytic RNA Catalyze either the hydrolysis of one of their own phosphodiester bonds or hydrolysis of bonds in other RNA molecules Been found to catalyze the aminotransferase activity of the ribosome Monika Martick and William G Scott Tertiary Contacts Distant from the Active Site Prime a Ribozyme for Catalysis Cell 126 309 320 2006 Data Storage by DNA George Church lab Harvard Univ One gram of DNA can store 700 terabytes of data That s 14 000 50 gigabyte Blu ray discs in a droplet of DNA that would fit on the tip of your pinky To store the same kind of data on hard drives the densest storage medium in use today you d need 233 3TB drives weighing a total of 151 kilos End of Lecture 11