DNA History and Replication

Scientific History The march to understanding that DNA is the genetic material Mendel Miescher Griffith Rosalind Franklin Watson & Crick Chagraff

Rags to Riches Mendel – Father of Genetics Discovered Genes by experimenting with pea plants Miescher –Discovered “Nuclein” Collected rags from infected war wounds.

The “Transforming Factor” 1928 Frederick Griffith Streptococcus pneumonia bacteria was working to find cure for pneumonia harmless live bacteria mixed with heat-killed infectious bacteria causes disease in mice substance passed from dead bacteria to live bacteria = “Transforming Factor”

Confirmation of DNA Hershey & Chase classic “blender” experiment worked with bacteriophage viruses that infect bacteria grew phage viruses in 2 media, radioactively labeled with either 35 S in their proteins 32 P in their DNA infected bacteria with labeled phages 1952 | 1969 Hershey Why use S ulfur vs. P hosphorus?

Protein coat labeled with 35 S DNA labeled with 32 P bacteriophages infect bacterial cells T2 bacteriophages are labeled with radioactive isotopes S vs. P bacterial cells are agitated to remove viral protein coats 35 S radioactivity found in the medium 32 P radioactivity found in the bacterial cells Which radioactive marker is found inside the cell? Which molecule carries viral genetic info? Hershey & Chase

Rosalind Franklin ( )

Structure of DNA Watson & Crick developed double helix model of DNA other scientists working on question: Rosalind Franklin Maurice Wilkins Linus Pauling 1953 | 1962 Franklin Wilkins Pauling

Chargaff DNA composition: “Chargaff’s rules” varies from species to species all 4 bases not in equal quantity bases present in characteristic ratio humans: A = 30.9% T = 29.4% G = 19.9% C = 19.8% 1947 That ’ s interesting! What do you notice?

Nucleotides and DNA structure

DNA Strand – Double Helix

Directionality You need to number the carbons! it matters! OH CH 2 O PO 4 N base ribose nucleotide This will be IMPORTANT!!

DNA Replication Replicate means to copy. DNA Replication – Copying of DNA

Steps of DNA Replication 1.The DNA strands separate (H bonds break) 2.New nucleotides are added to the separated strands 3.2 identical strands are created 14

Step 1: Unzipping DNA Helicase latches on at the ORIGIN OF REPLICATION. DNA Helicase then UNZIPS the DNA Strand. At each ORIGIN OF REPLICATION a REPLICATION BUBBLE IS FORMED.

Step 2: Transcription DNA Polymerase attaches to the TEMPLATE and adds complimentary bases to form a new DNA strand. DNA Polymerase works 5’ to 3’ know as the Leading Strand It cannot go 3’ to 5’. So the 3’ to 5’ strand has to be done in chunks called OKAZAKI fragments.

Step 3: Termination Ligase comes behind and closes the gap between Okazaki fragments. There is then two “Daughter” strands of DNA.

DNA Replication Summary 1.The DNA strands separate (H bonds break) 2.New nucleotides are added to the separated strands 3.2 identical strands are created