3. Defined: Molecule that stores genetic information Monomer: Nucleotide Millions of nucleotides bond to make nucleic acids Gene: section of DNA that holds instructions to build a protein

4. Nucleotide Structure Three parts –Sugar molecule –Phosphate group –Nitrogen base (A, T, C, or G) Nucleotides combine to make nucleic acids A pairs with T C pairs with G T C G A C

6. The nitrogen containing bases are the only difference in the four nucleotides Nucleotides can be divided into 2 categories:

7. Sugar (Deoxyribose) connects with the phosphate group 4 Different Bases: –Adenine (A) –Thymine (T) –Guanine (G) –Cytosine (C) Chargaff’s rules –Rule: A always joins with T –Rule: C always joins with G Human DNA: ~3 billion pairs CTAATGT

8. James Watson and Francis Crick identified DNA’s structure in 1953 (see video clip: Structure of DNA) Double Helix: spiral shape of DNA Nucleotide strands are connected by a hydrogen bond

9. 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

10. Step 1: DNA Helicase “unzips” the two DNA strands (breaks the H bonds) DNA Helicase Step 2: Free floating nucleotides (A, T, C, G) match up Step 3: DNA Polymerase reconnects the two strands DNA polymerase Both strands are identical Both strands are composed of a single strand of old and a single strand of new nucleotides. This is called the semi conservative model DNA Polymerase

11. DNA Replication Video Clip

12. Mutation: change in DNA sequence Mutations can be corrected –DNA Polymerase (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 enzyme

13. ReView 1.Name the three parts of a DNA nucleotide. 2.Name the four nitrogen bases and how they pair with others. 3.Which nitrogen based are pyrimidines? Purines? 4.List what takes place during the three stages of DNA replication. 5.Explain the semi-conservative model. 6.Fill in the missing DNA nucleotides: A C ? T ? ? ? G C T ? ? A ? C ? T T ? ? C ? T A T ? ? ? C A ? G ? G ? ? 6.Where is the DNA mutation? T A G G C C T G T C G A A C A G T A T C C G G A C A A C T T G T C A