Passing on Life’s Information DNA Replication

Nucleotides

T.H. Morgan Genes are located on chromosomes

Transformation (Griffith 1928)

Avery, McCarty, MacLeod (1944) Genetic Material Protein or DNA ???? "Studies on the chemical nature of the substance inducing transformation of pneumococcal types"

Hershey & Chase (1952)

Chargaff’s Rule Adenine – Thymine Guanine - Cytosine

Watson & Crick

Maurice Wilkins X-ray diffraction

Rosalind Franklin

Nucleotides

X-ray Data

DNA Structure

Complimentary Strands

Semiconservative Model (Meselson & Stahl)

Origin of Replication

Antiparallel

Enzymes DNA Polymerase Helicase Single-strand binding protein Topoisomerase RNA primase Ligase

RNA Primer Uses RNA primase to build RNA primer Eventually replaced with DNA by DNA Polymerase

DNA Replication

Leading and Lagging Strands Leading Strand Built in the 5’-3’ direction Built toward the replication fork Built continuously Uses one RNA Primer Lagging Strand Built in the 5’-3’ direction Built away from the replication fork Built discontinuously using Okazaki fragments Many RNA Primers

Overview

Proofreading DNA – 3.2 billion base pairs Mistake – 1/100,000 After corrections – 1/1,000,000

End-replication Problem Nucleotides can only be added to 3’ end Leaves gap on leading strand Each replication causes DNA molecule to get smaller

Telomeres

End of DNA strand made up of reoccurring DNA sequence Can be rebuilt with telomerase (only in germ-line cells)