DNA

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

Nucleotides? How many

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

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

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

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

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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

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