The Molecule of Life

Rosalind Franklin & Maurice Wilkins Important Scientists in the Discovery Of DNA Rosalind Franklin & Maurice Wilkins X-ray crystallographic images of DNA Photo 51 James Watson, Francis Crick Used x-ray crystallography images & models to figure out double helix structure

Chains of nucleotides, phosphodiester bonds Basic Structure Chains of nucleotides, phosphodiester bonds Dehydration reaction

Double helix, 2 strands of anti- parallel DNA nucleotides Ladder-like Basic Structure Double helix, 2 strands of anti- parallel DNA nucleotides Ladder-like Sugar,P on outside (sides of ladder) Bases on inside (rungs of ladder) Base pairing- Always A/T, G/C (purine/pyrimidine) H bonds between bases Entire molecule twisted in helix shape

3’ 5’ 3’ 5’

DNA replication is semi-conservative The instructions For making each new strand Are contained in the old, Parent strand!!! http://www.lewport.wnyric.org/JWANAMAKER/animations/DNA%20Replication%20-%20long%20.html

The Players Helicase-enzyme which “unzips” the helix by breaking hydrogen bonds Begins at origin of replication, creates “Y” replication fork DNA Polymerase-enzyme which builds the new strands of DNA “reads” base on parent strand, adds complementary base to new strand Only moves in one direction!!!!-moves 3’(OH) to 5’(P) Leading strand-built continuously, in one piece, toward the replication fork Lagging strand-built in pieces called Okazaki fragments, away from the fork DNA ligase-puts Okazaki fragments together

Origin of replication-where DNA synthesis starts Helicase first binds here

Steps in DNA synthesis…. Helicase unzips helix at origin of rep., forming replication fork DNA polymerase reads bases on leading strand, places complementary nucleotides in place as it moves toward rep. Fork On lagging strand, DNA polymerase builds new strand in Okazaki fragments-DNA ligase joins them together This continues until the ends of the parent strands are reached

Why can’t the lagging strand be built continuously? The replication fork continues to grow and…. DNA polymerase can’t go “backwards”

DNA repair                                                                           DNA polymerase proofreads its work as it goes along & fixes most mistakes!!!!

Using your Textbook, answer questions (complete sentences) section 10-1 review: #4