DNA History of DNA Frederick Griffith Bacteria contain

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 – 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.

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

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

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”)

Base Pairing 2 bonds • Nitrogenous bases connect together with hydrogen bonds 3 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 Replication • Step 3: New DNA molecules wind back up to form a double helix – Why do we say DNA replication is “Semiconservative? ” – There are now two DNA molecules, each containing one OLD strand one NEW strand Helicase DNA Polymerase

DNA Replication video