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

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

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

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

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 DNA polymerase Both strands are identical Both strands are a mix of old and new nucleotides

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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 enzyme

Kobe Kuiz Name the three parts of a DNA nucleotide. Name the four nitrogen bases and how they pair with others. Fill in the missing DNA nucleotides: A C ? T ? ? ? G C T ? ? A ? C ? T T ? ? C ? T A T ? ? ? C A ? G ? G ? ? List what takes place during the three stages of DNA replication. 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