BIO 151 1st Edition Lecture 10 Outline of Last Lecture 1. But what was a gene?2. Bacteria growing in a dish (bacterial "culture") can be transformed (Griffith 1920-30s)3. Virus DNA infects cell4. Hershey-Chase (1952)5. 1947: Chargaff's Analysis of DNA6. DNA is it. What's the structure?7. DNA double helix8. Nucleotides covalently linked into "strand" that can contain any sequence of nucleotides ("bases) in any order9. Nucleotides ("bases") on one strand hydrogen bond to "complementary" nucleotides on other strand = base pairing10. Two "strands" of helix run in opposite directions11. Accurate replication is important because...Outline of Current Lecture 1."Central Dogma" - from DNA to RNA to protein2. Processes shared by all 3 "domains" of cellular life3. Messelson and Stahl (1954)4. Proteins in DNA replication5. DNA replication: The big picture6. Problem 1 - Unwinding a helix creates supercoiling7. Problem 2 - DNA polymerase can only add bases to extant DNA or RNA strand8. Problem 3 - Polymerase only works in one direction (adds bases to free 3' end)9. Problem 4 - Cells with linear chromosomes: how do you replicate the ends?10. TelomeraseCurrent Lecture - 2/11/15- replication: DNA used to make identical DNA - DNA used to make RNA- RNA used to make protein- proteins made at ribosomesProcesses shared by all 3 "domains" of cellular life:1) Eukaryotes - cells have nucleus (karyon), internal membrane-wrapped region that contains many linear chromosomes- Prokaryotes - wrapped region that contains many linear chromosomes2)Bacteria3) Archaea- DNA replication (copying): old strand is "template" for making new complementary strand = "semi-conservative" - start - separate strands - add matching nucleotides - ligate (link them)- semi-conservative model --Watson and CrickThese 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.-2 strands of the parental molecule separate, and each functions as a template for synthesis of a new complementing strand- conservative model --the parental double helix remains intact and a second, all-new copy is made- dispersive model --each strand of both daughter molecules contains a mixture of old and newly synthesized partsMesselson and Stahl (1954):- label DNA with different isotopes of nitrogen: original DNA denser 15N, new DNA less dense 14N- density gradient in test tube- DNA with heavier 15N sinks further than DNA with light 14NProteins in DNA replication:1) Separation of strands (using helicase)-stabilization of exposed strands by binding proteins2) Linking new nucleotides releases 2 phosphates-enzyme - DNA polymeraseDNA replication: The big picture:1) Base pairing to make exact copy2) Semi-conservative replication - conservative strand of helix, make new strand3) Requires helicase to unwind, binding proteins to stabilize single strands, DNA polymerase to add, link new bases- origin of replication = site where helicases and polymerases start replication- process run in both along original DNA- makes replication bubble- prokaryotic, smaller circular chromosomes have one origin of replication- eukaryotes: have long linear chromosomes, each with one origin of replicationProblem 1 - Unwinding a helix creates supercoiling:- solution - topoisomerase cuts strands, allows them to unwind, and then re-joins themProblem 2 - DNA polymerase can only add bases to extant DNA or RNA strand:- so primase builds RNA "primer"- DNA polyermase replace primer with replicating DNA from other sideProblem 3 - Polymerase only works in one direction (adds bases to free 3' end):- replication of lagging strand has to keep re-starting on newly exposed strand- generates "Okazaki fragments", joined (ligated) by DNA ligase- origin of replication = unzipping strands at replication forks form replication bubble- leading strand on one side of origin is lagging strand on the otherProblem 4 - Cells with linear chromosomes: how do you replicate the ends?:- RNA primer usually replaced by DNA polymerase from the adjacent Okasaki fragment- but without DNA 5' of primer, polymerase can't work, primer lost- telomere = end of chromosome- also, ends of DNA more fragile, tend to fall apartTelomerase:- enzyme that adds nucleotides to template strand, making extension where RNA primer can bind- not made in most cells, is made in -1. germ line cells (sperm, eggs)2. stem cells3. cancer cells-makes them
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