Unit: Genetics Lesson: DNA and DNA Replication Agricultural Biology Student Objectives • Students will be able to identify and explain DNA structure. • Students will understand how DNA pairs with specific bases and the process of DNA replication. • Students will comprehend the importance of checking for errors I. DNA Structure • A) Double helix held together by weak hydrogen bonds • B) Nucleotides – 1. Subunits that make up DNA – 2. Made of 3 components • A) phosphate group • B) deoxyribose = 5-carbon sugar • C) nitrogen containing base I. DNA Structure • C) Four nitrogen bases – 1. Purines • A) Adenine • B) Guanine – 2. Pyrimidines • A) Thiamine • B) Cytosine I. DNA Structure II. Pairing Between Bases • A) Purines on 1 strand always pair with Pyrimidines on another strand – 1. A pairs with T always – 2. G pairs with C always • B) Complementary Strands – 1. Sequence of bases on one strand determines the sequence on the other strand. – 2. Make up the double helix and serve as a template to build DNA II. Pairing Between Bases III. DNA Replication • A) Step 1 = double helix unwinds – 1. DNA Helicase • A) an enzyme that breaks apart the hydrogen bonds – 2. Hydrogen Bond • A) these bonds hold nucleotides together – 3. Proteins • A) attach to the strands to keep the bonds from reforming – 4. Replication Forks • A) two areas where the DNA opens up to allow replication to occur III. DNA Replication • B) Step 2 = nucleotides are added – 1. DNA Polymerase • A) enzyme that moves along each strand adding nucleotides III. DNA Replication • C) Step 3 = 2 strands of DNA are formed – 1. Enzyme • A) DNA Polymerase remains attached until all of the DNA is replicated – 2. New DNA • A) once process is completed, 2 new strands are completed – 3. Nucleotide Sequence • A) identical sequences are present on both strands IV. Checking for Errors • A) Proofreading – 1. The Polymerase can only add a nucleotide if the previous one was correctly placed • B) Backtracking – 1. DNA can go back and remove the incorrect nucleotide and replace it with the correct one