1. DNA = Deoxyribonucleic Acid
Carries coded information that controls the traits of living things

2. How can DNA be seen?
X-ray Crystallography: tool used for identifying the atomic and molecular structure of a crystal

3. The First X-Ray Crystallography 1952
Taken by Rosalind Franklin
Revealed that DNA:
Is double stranded
Has a helix structure
Made of repetitive pieces
Is long and thin

4. James Watson and Francis Crick
Awarded Nobel Prize in 1953 for “discovering” the structure of DNA

5. What is DNA built from?

6. Monomer: Nucleotide
Nitrogen base
Phosphate group
Deoxyribose sugar

7. The name of nucleotide is determined by base it contains.

8. How is DNA put together?

9. Nucleotides are joined in any order
Sequence creates a code
Backbone/ sides- sugar and phosphate

10. Bases: point inward
Hydrogen bonds hold the bases together.
Sides are antiparallel.

11. Strands are identified by a numbering system… based on orientation (position) of sugar5’ 3’ 5’ 3’

12. Importance of the Sequence of Bases
The order determines the information it stores
Change in the order = change in the traits

13. Summary of DNA Structure
Double stranded
Helical (helix) shape
Sides are anti-parallel
Complementary bases
Repeating monomers (nucleotides)

14. DNA REPLICATION

15. How (and WHY) does DNA make copies of itself?
Process: Replication
Purpose: to make exact copies of DNA (must occur before a cell divides)
Each cell needs a copy of the info in DNA in order to grow
Occurs: in the nucleus

16. Step 1: DNA “Unzips” Weak hydrogen bonds break
Two strands separate (each strand is a template)
The enzyme helicase uncoils and unzip the double helix by separating the base pairs

17. Step 2: Pairing of Nucleotides
Free DNA nucleotides pair up with complementary base (A-T and C-G)
Uses DNA polymerase to pair them

18. Step 3: Binding Nucleotides bind to each other (H-bonds reform)
Uses DNA ligase (like a molecular “glue”)
Results in 2 new DNA molecules – each has a strand from the parent molecule and a new complimentary strand

19. How is accuracy insured?

20. Accuracy Original side  template Each new DNA molecule will have
One strand that is the original
One strand that is new
Both are identical to the template strand
DNA polymerase also “proofreads”
DNA polymerase initially makes about 1 in 10,000 base pairing errors
Enzymes proofread and correct these mistakes
The new error rate for DNA that has been proofread is 1 in 1 billion base pairing errors
Certain chemicals & ultraviolet radiation damage the DNA in our body cells
Cells must continuously repair DAMAGED DNA
Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA
DNA polymerase and DNA ligase replace and bond the new nucleotides together

21. Called Semi -Conservative Replication: “one DNA strand is “conserved” (saved)

22. How is DNA copied so quickly?
Both strands are copied at almost the same time
Copied in opposite directions

23. Faster strand is leading strand
One strand is copied slightly slower …lagging strand

24. More Replication Details…..
Add additional terms in red to your notes.

25. DNA polymerase adds new complementary nucleotides to the 3’ end.

26. The leading strand is built continuously.
The lagging strand is built in fragments and then glued together by ligase.

27. Final product!
Two new double stranded DNA molecules are produced by semi-conservative replication.