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

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

Sugar (Deoxyribose) connects with the phosphate group 4 Different Bases: –Adenine (A) –Thymine (T) –Guanine (G) –Cytosine (C) Chargaff’s Rules: –Rule: amount of A = amount of T –Rule: amount of C = amount of G Human DNA: ~3 billion pairs CTAATGT

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 Both DNA molecules are identical Both DNA molecules contain one original strand and one new strand. This is called the: semiconservative model DNA Polymerase

DNA Replication Video Clip

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

YouTube: DNA Repair

The Secret of Our Lives: The Human Genome Project

Code For Life: The Human Genome

Review 1)Name the three parts of a DNA nucleotide. 2)Name the four nitrogen bases. 3)List Chargaff’s rules. 4)Fill in the missing DNA nucleotides: A C ? T ? ? ? G C T ? ? A ? C ? T T ? ? C ? T A T ? ? ? C A ? G ? G ? ? 5)List what takes place during the three stages of DNA replication. 6)What type of organic moleules are DNA helicase and DNA polymerase? 7)Why is DNA replication considered semiconservative? 8)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