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Explore the nature of DNA as the genetic material in cells and its ability to store information, replicate, and undergo mutations. Learn about the scientists who made crucial discoveries and understand the process of DNA replication.
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In the beginning… • Is the genetic material in cells protein or DNA? • In order to be the genetic material, it must be… • Able to store information that pertains to the development, structure and metabolic activities of the cell • Stable so that it can be replicated • Able to undergo changes (mutations) to allow for genetic variation and evolution
The BIG Question… • How can DNA carry the genetic code? • Proteins contain 20 different amino acids that can be organized in countless ways to determine traits • Nucleic acids only contain 4 different nucleotides
Scientists that helped us figure it out… • Frederick Griffith • Was trying to find a vaccine against pneumonia • Found that one type of bacteria could turn into another (transformation) • Avery • Determined that Griffith’s results were due to DNA and not protein
Scientists that helped us figure it out… • Hershey – Chase • Worked with viruses that infect bacteria (bacteriophages) • Used radioactive sulfur to tag protein and radioactive phosphorus to tag DNA • The radioactive DNA moved into the bacteria • Proved that DNA is the genetic material in viruses
Scientists that helped us figure it out… • Chargaff • Compared ratios of the 4 nucleotides • Found that in every species A = T and G = C • This is known as Chargaff’s rule • Pyrimidine nucleotides – single ringed • thymine and cytosine • Purine nucleotides – double ringed • adenine and guanine • Always match a pyrimidine with a purine
Scientists that helped us figure it out… • Franklin and Wilkens • Used X-ray diffraction to take pictures of DNA
Scientists that helped us figure it out… • Watson and Crick • Put it all together and made the model! • DNA is a double helix • Sides of the ladder are deoxyribose and phosphate groups. These are held together by covalent bonds • The rungs of the ladder are the nitrogenous bases. These are held together by hydrogen bonds
More DNA deets • DNA is a polymer of nucleotides: • One base • Sugar – deoxyribose • Phosphate group • The deoxyribose carbons are numbered: • 1’ nitrogenous base • 5’ phosphate group • 3’ (hydroxide group) next phosphate group • The chains lie side by side in an antiparallel orientation • 5’ end to 3’ end
DNA Replication… • The process by which DNA makes a copy of itself • Occurs during interphase, before cell division • Semi-conservative: half of the original strand is always conserved to make the new strand • Enzymes are involved: • DNA helicase: separates the strands of the DNA molecule by breaking the hydrogen bonds between the nitrogenous bases – this forms a replication fork • DNA polymerase: moves from the 3’ end toward the 5’ end of the template strand and adds nucleotides • DNA ligase: binds the Okakazi fragments together
Replication… • New nucleotides can only be added in the 5’ to 3’ direction. • The side where this happens easily is called the leading strand. • The opposite strand is the lagging strand. Small sections are worked on. These new sections are called Okakazi fragments. • There are multiple replication forks all up and down the DNA strand.
http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swfhttp://www.stolaf.edu/people/giannini/flashanimat/molgenetics/dna-rna2.swf • http://highered.mcgraw-hill.com/olc/dl/120076/bio23.swf http://www.mcb.harvard.edu/Losick/images/TromboneFINALd.swf
