History, Structure, Replication (everything) DNA History, Structure, Replication

Discovery of the Genetic Material Griffith – studied the bacteria that causes pneumonia in mice; this disease-causing factor could be passed between two strains of bacteria Avery – using the same type of cells as Griffith, broke the strains down to the component macromolecules to determine nucleic acids (DNA) were responsible for the transformation Hershey and Chase – confirmed DNA was the transforming factor by using radioactive labeling in viruses

DNA Structure Levene – basic structure of nucleotides Sugars Five carbon sugar, phosphate group, and nitrogenous base Many nucleotides compose a nucleic acid (DNA or RNA) Sugars DNA – deoxyribose (one less oxygen) RNA – ribose Nitrogenous Bases Guanine (G) and adenine (A) – double rings (purine) Thymine (T) and cytosine (C) – single rings (pyrimidine)

Deoxyribonucleic Acid

Chargaff’s Rule Amount of A = T and amount of C = G which means… Chromosome consists of 51-245 million base pairs Yet stretched out its 5 cm long...so how does it fit? Tightly coils around histones DNA + histone = nucleosome They’re paired! 5th Period stopped here

Wilkins, Franklin, Watson, and Crick Photo 51 via x-ray diffraction (Franklin in Wilkins’ lab) DNA Structure (Watson and Crick) Two outside strands containing an alternating phosphate and sugar Cytosine and Guanine paired together by three hydrogen bonds Thymine and adenine paired together by two hydrogen bonds Double helix/twisted ladder Controversies in science Aiming x-rays at the DNA molecule Why 3 v. 2?

We’ll talk about these numbers 3 and 5 later… Hydrogen bonds!

So that’s the Structure, how is it replicated? Semiconservative replication – one strand serves as a template (Watson and Crick)

The Process Unwinding – DNA Helicase Starts at replication fork Hydrogen bonds are broken RNA Primase follows behind to add an RNA primer Orientation – 3’ and 5’ ends (next slide) These are enzymes RNA Primer – serves at the starting point for DNA polymerases Note how the 3 and 5 are at opposite ends for each of the strands…

New Old The process (cont.) DNA Polymerase (III) adds the appropriately paired nucleotides to the template DNA strand The template strand is read from the 3’ to the 5’ end The new strand is created in the 5’ to the 3’ orientation antiparallel to the original one Old New

Leading and Lagging Strands Because the template strand is always read from the 3’ to the 5’ end, it is “easier” for DNA polymerase to replicate one of the template strands (leading strand). Okazaki Fragments result in the lagging strand

Conclusion DNA replication occurs in many places on the chromosome at once Another DNA polymerase (I) comes through and replaces the RNA Primers with nucleotides DNA Ligase links the many fragments of DNA Including the Okazaki fragments Prokaryotic replication – one origin of replication (DNA is called a plasmid) Transformation – bacteria extracts DNA from an outside source