Unit: GeneticsUnit: GeneticsLesson: DNA and DNA Lesson: DNA and DNA ReplicationReplication

Agricultural BiologyAgricultural Biology

Instructor: Instructor:

Student ObjectivesStudent Objectives

• Students will be able to identify and Students will be able to identify and explain DNA structure.explain DNA structure.

• Students will understand how DNA pairs Students will understand how DNA pairs with specific bases and the process of with specific bases and the process of DNA replication.DNA replication.

• Students will comprehend the Students will comprehend the importance of checking for errors importance of checking for errors

I. DNA StructureI. DNA Structure

• A) Double helix held together by weak A) Double helix held together by weak hydrogen bondshydrogen bonds

• B) NucleotidesB) Nucleotides– 1. Subunits that make up DNA1. Subunits that make up DNA– 2. Made of 3 components 2. Made of 3 components

• A) phosphate groupA) phosphate group• B) deoxyribose = 5-carbon sugarB) deoxyribose = 5-carbon sugar• C) nitrogen containing base C) nitrogen containing base

I. DNA StructureI. DNA Structure

• C) Four nitrogen basesC) Four nitrogen bases– 1. Purines 1. Purines

• A) Adenine A) Adenine • B) Guanine B) Guanine

– 2. Pyrimidines 2. Pyrimidines • A) Thiamine A) Thiamine • B) Cytosine B) Cytosine

I. DNA StructureI. DNA Structure

II. Pairing Between BasesII. Pairing Between Bases• A) Purines on 1 strand A) Purines on 1 strand alwaysalways pair with pair with

Pyrimidines on another strandPyrimidines on another strand – 1. A pairs with T 1. A pairs with T alwaysalways– 2. G pairs with C 2. G pairs with C alwaysalways

• B) Complementary StrandsB) Complementary Strands – 1. Sequence of bases on one strand 1. Sequence of bases on one strand

determines the sequence on the other determines the sequence on the other strand.strand.

– 2. Make up the double helix and serve as a 2. Make up the double helix and serve as a template to build DNAtemplate to build DNA

II. Pairing Between BasesII. Pairing Between Bases

III. DNA ReplicationIII. DNA Replication

• A) Step 1 = double helix unwindsA) Step 1 = double helix unwinds– 1. DNA Helicase 1. DNA Helicase

• A) an enzyme that breaks apart the hydrogen bondsA) an enzyme that breaks apart the hydrogen bonds– 2. Hydrogen Bond2. Hydrogen Bond

• A) these bonds hold nucleotides togetherA) these bonds hold nucleotides together– 3. Proteins3. Proteins

• A) attach to the strands to keep the bonds from A) attach to the strands to keep the bonds from reforming reforming

– 4. Replication Forks4. Replication Forks• A) two areas where the DNA opens up to A) two areas where the DNA opens up to allow allow

replication to occur replication to occur

III. DNA ReplicationIII. DNA Replication

• B) Step 2 = nucleotides are addedB) Step 2 = nucleotides are added– 1. DNA Polymerase1. DNA Polymerase

• A) enzyme that moves along each strand A) enzyme that moves along each strand adding nucleotides adding nucleotides

III. DNA ReplicationIII. DNA Replication

• C) Step 3 = 2 strands of DNA are formed C) Step 3 = 2 strands of DNA are formed – 1. Enzyme1. Enzyme

• A) DNA Polymerase remains attached until all of A) DNA Polymerase remains attached until all of the DNA is replicatedthe DNA is replicated

– 2. New DNA2. New DNA• A) once process is completed, 2 new strands are A) once process is completed, 2 new strands are

completed completed

– 3. Nucleotide Sequence 3. Nucleotide Sequence • A) identical sequences are present on both strands A) identical sequences are present on both strands

IV. Checking for Errors IV. Checking for Errors

• A) Proofreading A) Proofreading – 1. The Polymerase can only add a nucleotide 1. The Polymerase can only add a nucleotide

if the previous one was correctly placed if the previous one was correctly placed

• B) BacktrackingB) Backtracking– 1. DNA can go back and remove the 1. DNA can go back and remove the

incorrect nucleotide and replace it with the incorrect nucleotide and replace it with the correct one correct one