1. The Molecule of Life

2. 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

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

4. 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

5. 3’ 5’ 3’ 5’

7. DNA replication is semi-conservative
The instructions For
making each new strand
Are contained in the old,
Parent strand!!!

8. 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

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

10. 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

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

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

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