DNA Structure and Replication Chapter 16

A brief history… Friedrich Miescher discovers nuclein by extracting white blood cells from pus-laden bandages: 1869

Frederick Griffith NHS epidemiologist tried to find a pneumonia vaccine Found “transforming principle” instead

Griffith’s Experiment Dead S+ Live R Live R Dead S Live S

Avery, McCarty, McLeod Followed up on Griffith’s experiment Demonstrated that DNA was Griffith’s “transforming principle”

Hershey and Chase Used phages to demonstrate that DNA was genetic material Radiolabeled phages with 35S and 32P to distinguish protein from nucleic acid

Erwin Chargaff Devised nucleotide base pairing rules based on data that showed roughly equivalent percentages of adenine and thymine, cytosine and guanine A-T; G-C pair up

Franklin and Wilkins Used x-ray diffraction to produce a photograph of DNA’s double helix structure

Watson and Crick Utilized data from multiple sources to deduce the structure of DNA Won Nobel Prize with Wilkins, 1963

Building Blocks of DNA DNA, a nucleic acid, is made of nucleotides: 5-carbon sugar Phosphate group Nitrogen base

Nitrogen Bases: Pyrimidines Single ring structures: Thymine Cytosine

Nitrogen Bases: Purines Double ring structures: Adenine Guanine

Base Pairing Rules Adenine pairs with thymine Guanine pairs with cytosine

DNA Structure Minor groove Major groove Phosphodiester bonds make up the sides of the helix Hydrogen bonds hold the nitrogen bases across the center Minor groove Major groove

Antiparallel Structure Sugar carbons are numbered 1’-5’ One side of DNA runs in the 3’ direction The other side runs in the 5’ direction This is important to replication

DNA Replication Where? When? Enzymes responsible?

DNA Replication Replication fork An enzyme called primase adds RNA nucleotides to create a short primer (in yellow) Single-stranded binding proteins (SSBs) hold the two halves of the helix apart An enzyme called DNA helicase unwinds the helix DNA polymerase adds complementary nucleotides to RNA primer in 5’ 3’ direction

DNA Replication Lagging strand produces Okazaki fragments. DNA ligase joins these fragments together Side of DNA synthesized from 5’3’: leading strand. This is synthesized continuously Side of DNA synthesized from 3’5’: lagging strand. This is NOT synthesized continuously.

DNA Replication