1. DNA

2. Deoxyribonucleic Acid
Defined: Molecule that stores genetic information
Nucleotides: Three repeating units of nucleic acids
1) Sugar
2) Phosphate Group
3) Nitrogen Base
Millions of nucleotides per strand of DNA
Deoxyribonucleic
Acid

3. Nucleotides?
How many

4. Sugar (Deoxyribose) connects with the phosphate group
4 Different Bases:
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Rule: A always joins with T
Rule: C always joins with G
Human DNA: ~3 billion pairs
Nucleotides C T A A T G T

5. Double Helix
James Watson and Francis Crick identified DNA’s structure in 1953
Double Helix: spiral shape of DNA
Left and right nucleotide strands are connected by a hydrogen bond

7. DNA Replication Defined: Process of copying DNA
During interphase (S-stage)
Step 1: DNA Helicase “unzips” the two DNA strands (breaks the H bonds)
Step 2: Free floating nucleotides (A, T, C, G) match up
Step 3: DNA Polymerase reconnects the two strands

8. DNA Polymerase
Glues the DNA T A A T G C G C
Two Identical
Strands of DNA! A T C G T A A T G C G C C G T A C G A T
DNA Helicase
Splits the DNA

9. Video Clip

10. Accuracy & Repair Mutation: change in DNA sequence
Mutations can be corrected
Enzyme “proofreads” DNA and check/correct errors
Pre-repair: 1 in 10,000 nucleotides has an error
Post-repair: 1 in 1 billion nucleotides has an error
Accuracy &
Repair

11. Quick Review DNA nucleotides form long chains
DNA nucleotides have 4 different bases (A, T, C, G)
DNA makes exact copies of itself