DNA Structure and History

Frederick Griffith

discovered transformation in bacteria, showing that genetic material could be transferred

Oswald Avery

proved that dna is the genetic material, not proteins

Hershey & Chase

used bacteriophages to demonstrate that dna carries genetic information

Erwin Chargaff

discovered that a = t and c = g, which led to the base pairing rules.

Rosalind Franklin

used x-ray diffraction to reveal DNA's helical structure

Maurice Wilkins

worked with franklin and helped watson and crick discover dna's structure

Watson & Crick

built the first correct model of the dna double helix using Franklin's x-ray data

dna structure

a double helix made of two complementary strands

nucleotide

basic unit of DNA, consisting of a phosphate group, deoxyribose sugar, and a nitrogenous base

phosphate-sugar backbone

alternating sugar and phosphate groups that form the sides of the DNA ladder

base pairing

a pairs with t (2 hydrogen bonds) and c pairs with g (3 hydrogen bonds)

antiparallel strands

dna strands run in opposite directions (5' to 3' and 3' to 5')

replication

the process of copying dna for cell division, requiring helicase, polymerase, and ligase

helicase

unwinds and separates the two dna strands during replication

dna polymerase

adds complementary nucleotides to the growing dna strand during replication

okazaki fragments

short segments of dna on the lagging strand that are joined by ligase during replication