Rosalind Franklin took diffraction x-ray photographs of DNA crystalsIn the 1950’s, Watson & Crick built the first model of DNA using Franklin’s x-rays
Adenine must pair with ThymineGuanine must pair with Cytosine Bonded by hydrogen bonds Two strands coiled called a double helix Sides made of a sugar called Deoxyribose which are bonded to phosphate groups Center made of nitrogen bases bonded together by weak hydrogen bonds
Joining of Two Strands
“Rungs of ladder” (hoizontal lines) NitrogenousBase (A,T,G or C) and the “Legs of ladder” (vertical lines) are Phosphate & Sugar Backbonn Two strands of DNA open forming Replication Forks (Y-shaped region) New strands grow at the forks
Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds Before new DNA strands can form, the enzyme Primase must present to start the addition of new nucleotidesPrimase is the enzyme that begins the actual DNA copying process. DNA polymerase can then add the new nucleotides
Once DNA Polymerase has created the copies, Ligase “glues” the strands back together.