1. Molecular Biology of the Gene
Chapter 10
Molecular Biology of the Gene

2. THE STRUCTURE OF THE GENETIC MATERIAL
© 2012 Pearson Education, Inc. 2

3. Experiments showed that DNA is the genetic material
Requirements for the genetic material:
Must be able to code for unlimited amount of information
Must be stable
Yet able to change (everyone has a unique genetic sequence)
Until the 1940s, the case for proteins serving as the genetic material was stronger than the case for DNA.
Proteins are made from 20 different amino acids.
DNA was known to be made from just four kinds of nucleotides.
Student Misconceptions and Concerns
1. Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students.
2. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10.
Teaching Tips
1. A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA.
2. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
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4. Experiments showed that DNA is the genetic material
Frederick Griffith discovered that a “transforming factor” could be transferred into a bacterial cell.
Hershey and Chase experiment
Only radio-labeled DNA entered bacteria cell
Student Misconceptions and Concerns
1. Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students.
2. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10.
Teaching Tips
1. A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA.
2. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
Animation: Hershey-Chase Experiment
Animation: Phage T2 Reproductive Cycle
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5. Mixture of heat-killed S cells and living R cells Living S cells
(control)
Living R cells
(control)
Heat-killed
S cells (control)
RESULTS
Mouse dies
Mouse healthy
Mouse healthy
Mouse dies
Living S cells
are found in
blood sample

6. LE 16-3
Phage
head
Tail
Tail fiber
DNA
100 nm
Bacterial
cell

7. Figure 10.1A
Head
DNA
Tail
Tail fiber
Figure 10.1A Phage T2 7

8. Radioactive Sulfur used to label protein
Radioactive protein
Empty protein shell
Phage
The radioactivity is in the liquid.
Bacterium
Phage DNA
Batch 1: Radioactive protein labeled in yellow
DNA
Centrifuge
Pellet 1 2 3 4
Figure 10.1B The Hershey-Chase experiment
Batch 2: Radioactive DNA labeled in green
Radioactive DNA
Centrifuge
The radioactivity is in the pellet.
Pellet
Radioactive Phosphorous used to label DNA 8

9. 10.2 DNA and RNA are polymers of nucleotides
DNA and RNA are nucleic acids.
One of the two strands of DNA is a DNA polynucleotide, a nucleotide polymer (chain).
A nucleotide is composed of a
nitrogenous base,
five-carbon sugar, and
phosphate group.
The nucleotides are joined to one another by a COVALENT BOND between sugar-phosphate backbone.
Student Misconceptions and Concerns
1. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10.
2. Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases.
Teaching Tips
1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
2. Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are like a train of various lengths and combinations of four types of train cars (monomers). Proteins are also “trains” of various lengths but made of a combination of 20 types of train cars.
Animation: DNA and RNA Structure
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10. Thymine (T) Phosphate group
Cytosine (C)
Pyrimidines
Purines
Adenine (A)
Guanine (G)
Nitrogenous base (can be A, G, C, or T)
Thymine (T)
Figure 10.2B The nitrogenous bases of DNA
Phosphate group
Sugar (deoxyribose)
DNA nucleotide 10

11. Nitrogenous base (can be A, G, C, or U)
RNA
RNA (ribonucleic acid) is unlike DNA in that it
uses the sugar ribose (instead of deoxyribose in DNA) and
RNA has the nitrogenous base uracil (U) instead of thymine.
RNA is a single, linear strand
Phosphate group
Sugar (ribose)
Uracil (U)
Nitrogenous base (can be A, G, C, or U)
Student Misconceptions and Concerns
1. If your class has not yet studied Chapter 3, consider assigning module 3.15 on “Nucleic Acids” before addressing the contents of Chapter 10.
2. Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases.
Teaching Tips
1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
2. Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are like a train of various lengths and combinations of four types of train cars (monomers). Proteins are also “trains” of various lengths but made of a combination of 20 types of train cars.
© 2012 Pearson Education, Inc. 11

12. Cytosine Uracil Adenine Guanine Ribose Phosphate Figure 10.2D
Figure 10.2D A computer model showing part of an RNA polynucleotide 12

13. Sugar-phosphate backbone
The nucleotides are joined to one another by a COVALENT BOND between sugar-phosphate backbone. A T C G T A
Sugar-phosphate backbone C G
Phosphate group A T G C A G A
Nitrogenous base
Nitrogenous base (can be A, G, C, or T)
Covalent bond joining nucleotides A T G C
Sugar T A T A C C C C C G T A
DNA nucleotide
Thymine (T)
A DNA double helix T T T
Phosphate group
Figure 10.2A The structure of a DNA polynucleotide G G
Sugar (deoxyribose)
DNA nucleotide G G
Two representations of a DNA polynucleotide 13

14. Sugar–phosphate
backbone
Nitrogenous
bases
5 end
The nucleotides are joined to one another by a COVALENT BOND between sugar- phosphate backbone.
Thymine (T)
Adenine (A)
Cytosine (C)
Phosphate
DNA nucleotide
Sugar (deoxyribose)
3 end
Guanine (G)

15. Figure 10.3B
Figure 10.3B Watson and Crick in 1953 with their model of the DNA double helix 15

16. Franklin’s X-ray diffraction photograph of DNA
LE 16-6
Rosalind Franklin
Franklin’s X-ray diffraction
photograph of DNA

17. DNA is a double-stranded helix
In 1953, James D. Watson and Francis Crick deduced the secondary structure of DNA, using
X-ray crystallography data of DNA from the work of Rosalind Franklin and Maurice Wilkins and
Chargaff’s observation that in DNA,
the amount of adenine was equal to the amount of thymine and
the amount of guanine was equal to that of cytosine.
Student Misconceptions and Concerns
Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases.
Teaching Tips
1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
2. The authors note that the structure of DNA is analogous to a twisted rope ladder. In class, challenge your students to explain what the parts of the ladder represent. The wooden rungs represent pairs of nitrogenous bases joined by hydrogen bonds. Each rope represents a sugar-phosphate backbone.
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18. Chargaff’s Rule: Equal proportion of A:T and G:C

19. 10.3 SCIENTIFIC DISCOVERY: DNA is a double-stranded helix
Watson and Crick reported that DNA consisted of two polynucleotide strands wrapped into a double helix.
The sugar-phosphate backbone is on the outside.
The nitrogenous bases are perpendicular to the backbone in the interior.
Specific pairs of bases give the helix a uniform shape.
A pairs with T, forming two hydrogen bonds, and
G pairs with C, forming three hydrogen bonds.
Student Misconceptions and Concerns
Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases.
Teaching Tips
1. The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).
2. The authors note that the structure of DNA is analogous to a twisted rope ladder. In class, challenge your students to explain what the parts of the ladder represent. The wooden rungs represent pairs of nitrogenous bases joined by hydrogen bonds. Each rope represents a sugar-phosphate backbone.
Animation: DNA Double Helix
© 2012 Pearson Education, Inc. 19

20. Figure 10.3C
Figure 10.3C A rope ladder model for the double helix
Twist 20

21. Nucleotides in opposing strands are connected by HYDROGEN bonds
5 end
Hydrogen bond
3 end
1 nm
3.4 nm
3 end
0.34 nm
5 end
Key features of DNA structure
Partial chemical structure
Space-filling model
Notice the two nucleotide strands run anti-parallel (opposite) of each other!

22. Sugar Sugar Adenine (A) Thymine (T) Sugar Sugar Guanine (G)
LE 16-8
Sugar
Sugar
Adenine (A)
Thymine (T)
Sugar
Sugar
Guanine (G)
Cytosine (C)