DNA!

History of DNA Frederick Griffith Bacteria contain a molecule that gives the cell the information it needs to be harmful

History of DNA Oswald Avery Hershey and Chase The DNA is the molecule Griffith was talking about! Without DNA, the rough bacteria can’t “learn” how to become deadly Hershey and Chase Viruses also use DNA to store information about how to build new virus

DNA structure DNA (deoxyribose nucleic acid) is a nucleic acid The monomer is a nucleotide. Each nucleotide has three parts: a phosphate group, a sugar, and a nitrogenous base. The monomers of nucleic acids are nucleotides All nucleotides have a nitrogenous base, a sugar, and a phosphate group

Nucleotides (cont) Every nucleotide has a phosphate and a sugar Nitrogenous Bases vary between nucleotides

Nucleotides (cont) CUT the Py Purines - nucleotides with a 2-ring nitrogenous base Adenine and Guanine Pyrimidines - nucleotides with a 1-ring nitrogenous base Thymine and Cytosine CUT the Py

Nucleotide Bonding Dehydration synthesis reaction connects the phosphate group from one nucleotide to the sugar group from another nucleotide.

DNA polymer structure Double helix (two connected twists) Sugar and phosphates on the outsides (the “backbones”) Nitrogenous bases on the inside (the “ladder rungs”) How X-ray crystallography works: X rays are fired at DNA fibers. The scatter of the rays from the fibers is observed by catching the rays on photographic film (as many spots). The angle of the scatter represented by each x-ray spot on the film gives information about the position of an atom or certain groups of atoms in the DNA molecule. The interpretation of the spot patterns requires VERY complex mathematics. The available data suggests that DNA is long and skinny and that it has two parts that are parallel to each other. The x-ray data showed the molecule to be helical (spiral) in shape.

Base Pairing Nitrogenous bases connect together with hydrogen bonds

DNA Structure (Watson/Crick/Franklin)

DNA Replication

DNA Replication Why does a cell replicate it’s DNA? To make an identical copy! When would a cell need to do that? When it is dividing, so… To make new cells

DNA Replication Step 1: Helicase binds to the DNA and unwinds the 2 strands (exposing nitrogenous bases) What kinds of bonds does helicase break? Helicase

DNA Replication Step 2: DNA Polymerase adds complementary nucleotides to the exposed bases on the original strand This forms a NEW strand attached to the OLD one What kinds of bonds are being formed? Helicase DNA Polymerase DNA Polymerase

DNA Replication Step 3: New DNA molecules wind back up to form a double helix Why do we say DNA replication is “Semi-conservative?” There are now two DNA molecules, each containing one OLD strand and one NEW strand Helicase DNA Polymerase DNA Polymerase

DNA Replication video