Chapter 9
Section 1: Identifying the Genetic Material
Section 2: The Structure of DNA
Section 3: The Replication of DNA

Section 1
Identifying the Genetic Material
Objectives:
•
Relate Griffith's conclusions to the observations he made during the transformation experiments.
• Summarize the steps involved in Avery's transformation experiments, and state the results.
•
Evaluate the results of the Hershey and Chase experiment.

Section 1
Identifying the Genetic Material
Transformation
• Griffith’s Experiments
Griffith discovered that harmless bacteria could turn virulent when mixed with bacteria that cause disease. He discovered what is called transformation, a change in genotype when cells take up foreign genetic material.
• Avery’s Experiments Avery’s work demonstrated that
DNA is the genetic material responsible for transformation.

Section 1
Identifying the Genetic Material
Viral Genes and DNA
• DNA’s Role Revealed
Hershey and Chase used the bacteriophage T2 and radioactive labels to show that viral genes are made of DNA, not protein. DNA stores the information that tells cells which proteins to make and when to make them.

Section 2
The Structure of DNA
Objectives:
•
Describe the three components of a nucleotide.
•
Develop a model of the structure of a DNA molecule.
•
Evaluate the contributions of Chargaff, Franklin, and Wilkins in helping Watson and Crick determine the double-helical structure of DNA.
•
Relate the role of the base-pairing rules to the structure of DNA.

Section 2
The Structure of DNA
The Structure of DNA
•
A Winding Staircase DNA is made of two strands of nucleotides twisted into the form of a double helix.
• Nucleotides Each nucleotide in DNA is made up of the sugar deoxyribose, a phosphate group , and one of four nitrogen bases. The four nitrogen bases are found in DNA are adenine (A), thymine (T), guanine
(G), and cytosine (C).

Section 2
The Structure of DNA
Discovering DNA’s Structure
Chargoff’s Observations Chargoff’s data showed that for each organism the amount of adenine always equaled the amount of thymine. Likewise, the amount of guanine always equaled the amount of cytosine.
Wilkins and Franklin’s Photographs Wilkin’s and
Franklin’s X-ray diffraction photographs supported that DNA is a tightly coiled double helix.

Section 2
The Structure of DNA
Discovering DNA’s Structure continued
Watson and Crick’s DNA Model
Watson and Crick determined the double helix structure of DNA in
1952 with the help of data gathered by Wilkins,
Franklin, and Chargoff.
Pairing Between Bases The two strands of DNA are complementary—each A on one strand pairs with a T on the opposite strand, and each G on one strand pairs with a C on the opposite strand.

Section 3
The Replication of DNA
Objectives:
•
Summarize the process of DNA replication.
•
Describe how errors are corrected during DNA replication.
•
Compare the number of replication forks in prokaryotic and eukaryotic DNA.

Section 3
The Replication of DNA
Roles of Enzymes in DNA Replication
•
DNA Replication Before a cell divides, it copies its
DNA by a process called DNA replication. The results of DNA replication is two exact copies of the cell’s original DNA. Each new double helix is composed of one original strand and one new DNA strand.
•
DNA Replication Enzymes In DNA replication, enzymes work to unwind and separate the double helix and add complementary nucleotides to the exposed strands.

Section 3
The Replication of DNA
Roles of Enzymes in
DNA Replication continued
•
Checking for Errors DNA polymerase proofreads DNA during its replication so that very few errors occur.

Section 3
The Replication of DNA
The Rate of Replication
•
Replication Forks Eukaryotes meet the challenge of replicating all its DNA with multiple replication forks working in concert.