Lecture 26Outline of Last Lecture1) Summarize the evidence that accumulated during the 1940s and 1950s demonstrating that DNA is the genetic material.2) Illustrate how the two strands of DNA are oriented with respect to eachother (antiparallel).3) State the base-pairing rules for DNA, as determined by Chargaff and coworkers, and describe how complementary bases bind to each other.4) Sketch how nucleotide subunits link together to form a single DNA strand. Summarize how DNA replicates, focusing particularly on the different enzymes in the process.Outline of Current Lecture1) Explain how DNA is (a) bidirectional and (b) discontinuous in one strand and continuous in the other. What is an Okasaki Fragment and why is it needed?2) What does it mean to say that DNA synthesis is semi-conservative? 3) Why do cells have DNA repair enzymes?4) Define telomere; describe the possible connections between telomerase and cell aging and between telomerase and cancer.5) Who are these DNA pioneers and what was their claim to fame as scientists? Watson and Crick, Rosalind Franklin, Hershey and Chase, Erwin Chargaff. Optional: Griffith, Avery, Meselson and Stahl.I. DNA Direction- DNA is bidirectional in the double helix because there is a 5 prime and a 3 prime end, and one side of it is going 5’ to 3’, and the other is going 3’ to 5’ (but it’s just inversed.)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. BIOL 101 1st Edition- In terms of continuous and discontinuous, it relates to how DNA is replicated. Continuous replication occurs on the leading strand, which is just DNA polymerase synthesizing new DNA onto the strand in the 5’ to 3’ direction. On the lagging strand however, what occurs is a much more complicated process involving many different parts. Instead ofone continuous synthesizing of DNA, it is a discontinuous process, meaning some parts are halted in the process just to resume again.- Okazaki fragments are in the lagging strand in that big process. RNA polymerase synthesizes some RNA on the lagging strand for it to be turned into DNA polymerase, and the RNA fragment that is there prior to being turned into DNA is called an Okazaki fragment. It is basically the base unit to create DNA on the lagging strand, so without it DNA couldn’t be replicated.II. DNA Synthesis Conservatism- When DNA synthesis is called Semi-Conservative, it’s talking about the strands of the DNA. When DNA is synthesized, one side of the strand is original and kept, while one side of the strand is brand new. This is why it is semi-conservative.III. DNA Repair- DNA has an assortment of DNA repair enymes. These enzymes cleave and cut out any abnormalities that are causing a problem in the DNA. DNA isn’t always replicated perfectly, and normally doesn’t go under mitosis if the DNA is replicated incorrectly. The DNA repair enzymes are there to fixany problems.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. BIOL 101 1st EditionIV. Telomerase- When DNA is synthesized, the ends of the DNA are cut off, so a telomere is put there by telomerase to be cut off because it is only a repeated nucleotide with no real information. Telomeres also prevent the fusion of the end of the chromosomes to another chromosome.- After each successful replication of DNA, the telomeres become shortened, but can be restored by the telomerase enzyme. Eventually though, this enzyme wears out, and the DNA will messed up. Eventually, the cell cannot undergo proper mitosis and dies. This is a system of the cell aging process. - Proper mitosis doesn’t allow for messed up DNA, however in cancerous cells, proper mitosis is never gone through. When acancerous cell is dividing and the telomeres become too shortand the cell is nearing death by age, it activates the telomerase and continuously restores the telomeres to good length, thus making cancer cells immortal.V. DNA Pioneers- Watson and Crick proposed the double helix model as the structure of DNA.- Rosiland Franklin created a spectrograph image of DNA, whichled Watson and Crick to come to the conclusion of DNA’s structure.- Hershey and Chase put tracking radioactive electrons on viruses to see that phage’s inject cells with DNA, not protein. This led them to believe that DNA is the genetic material and not protein. - Chargaff created a rule stating that nucleotides in DNA have a1:1 ratio.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. BIOL 101 1st