BIOLCHEM 415 1st Edition Lecture 30Outline of Last Lecture I. Nucleic Acids are polymers that have a directionalityII. Nucleic Acids can form a double-helical structure but can adopt multiple formsIII. DNA needs to be compacted in order to fit in the cellOutline of Current Lecture IV. DNA replication is a semi-conservative processV. DNA synthesis is more complex in EukaryotesCurrent LectureDNA replication- every cell division- semi-conservation- hybrids: a new strand + an old strand- DNA polymerase = catalyst- DNA can be damaged- mutations: replication, chemical, radiation- polymerase in bacteria- 5 kinds- polymerase III is most important for replicationDNA polymerase- catalyzes formation of phosphodiester bonds- synthesis requires 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.1 – 4 dNTs2 – Mg2+3 – template strand4 – primer for new strand5 – polymerase- bonds formed at 3’ end- structure- polymerase I- shaped like hand, active site in “palm”- exonuclease- requires divalent metal ions (cofactors)Specificity of replication- correct H-bonding- shape of base- proofreadingDNA helicase separates strands of double helix- powered by ATP- Werner syndrome- helicase defect- premature agingTopoisomerases- DNA unwound for replication, supercoiling occurs - over winding- impedes replication and translation- induce or eliminate supercoils- antibiotics target bacterial topoisomerases- DNA gyrase essential for bacteriaReplication of bacterial chromosomes- replication is rapid- 2000 nucleotides/sec- plasmid (large circle)DNA replication of E. Coli- origin of replication- unique 245 bp site (oriC locus)Replication requires RNA primer- made by primase- short 5’-3’ segment- DNA polymerase I removes primer- replaces with DNA- with 5’ 3’ exonucleaseOne strand continuously replicated and one replicated in fragments- continuous = leading strand- fragments = lagging strand- Okazaki fragments- copied simultaneously Polymerase III- majority of synthesis - highlyprocessive- rarely releases substrate- sliding clamp (β2 subunit)Single strand binding protein (SSB)- keep strands separated behind helicasePolymerase III holoenzyme- cone enzymeLagging strand- looped down- trombone model- ligase creates intact strands- 3’ hydroxyl and 5’ phosphateDNA synthesis more complex in eukaryotes- have more DNA - multiple chromosomes with linear DNA- polymerase switching (αδ)- α initiates- primase and polymerase activity- δ more processive- extends chains- telomeres- located at the ends of chromosomes- one strand longer than the other (G-rich strand)- with each replication round the G-rich strand
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