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

2. DNA REPLICATION
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3. 10.4 DNA replication depends on specific base pairing
In their description of the structure of DNA, Watson and Crick noted that the structure of DNA suggests a possible copying mechanism.
DNA replication follows a semiconservative model.
The two DNA strands separate.
Each strand is used as a pattern to produce a complementary strand, using specific base pairing.
Each new DNA helix has one old strand with one new strand.
Student Misconceptions and Concerns
The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important.
Teaching Tips
1. Demonstrate the complementary base pairing within DNA. Present students with the base sequence to one side of a DNA molecule and have them work quickly at their seats to determine the sequence of the complimentary strand. For some students, these sorts of quick practice are necessary to reinforce a concept and break up a lecture.
2. The semiconservative model of DNA replication is like making a photo from a negative and then a new negative from the photo. In each new negative and photo pair, the new item was made from an old item.
Animation: DNA Replication Overview
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4. A parental molecule of DNA
Figure 10.4A_s1
A T
C G
G C
A T
T A
A parental molecule of DNA
Figure 10.4A_s1 A template model for DNA replication (step 1) 4

5. A parental molecule of DNA
Figure 10.4A_s2
A T T A A T
C G C G G C
G C G C C A
A T A T
Free nucleotides
T A T A
A parental molecule of DNA
The parental strands separate and serve as templates
Figure 10.4A_s2 A template model for DNA replication (step 2) 5

6. A parental molecule of DNA
Figure 10.4A_s3
A T T A A T
A T
A T
C G C G G
C G
C G C
G C G C C
G C
G C A
A T A T
A T
A T
Free nucleotides
T A T A
T A
T A
A parental molecule of DNA
The parental strands separate and serve as templates
Two identical daughter molecules of DNA are formed
Figure 10.4A-s3 A template model for DNA replication (step 3) 6

7. Problems and Solutions Associated with DNA Replication
Replication must occur quickly.
Multiple origin of replication sites are started along eukaryotic chromosomes.
DNA polymerase catalyzes DNA synthesis
Parental DNA molecule
Origin of replication
“Bubble”
Parental strand
Daughter strand
Two daughter DNA molecules
Student Misconceptions and Concerns
The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important.
Teaching Tips
1. To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter.
2. There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one error in every 1 billion words.
Animation: Origins of Replication
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8. Problems and Solutions Associated with DNA Replication
DNA strands are twisted around each other and must be separated
Helicase
Enzyme that unwraps DNA and separate H-bonds between strands
Student Misconceptions and Concerns
The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important.
Teaching Tips
1. To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter.
2. There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one error in every 1 billion words.
© 2012 Pearson Education, Inc. 8

9. Problems and Solutions Associated with DNA Replication
Replication must be accurate
DNA polymerase can proof-read its own work
Correct mistakes
Student Misconceptions and Concerns
The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important.
Teaching Tips
1. To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter.
2. There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one error in every 1 billion words.
© 2012 Pearson Education, Inc. 9

10. Problems and Solutions Associated with DNA Replication
DNA Polymerase can only add nucleotides to the 3’ end of a pre-exiting DNA strand
One-strand synthesized as a single continuous strand (leading strand)
The other (lagging strand) synthesized in small fragments (Okazaki fragments)
DNA Ligase connects these fragments
RNA polymerase (primase) starts replication by building a small, RNA primer
Student Misconceptions and Concerns
The authors note that although the general process of semiconservative DNA replication is relatively simple, it involves complex biochemical gymnastics. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important.
Teaching Tips
1. To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter.
2. There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one error in every 1 billion words.
© 2012 Pearson Education, Inc. 10

11. DNA strands run in opposite directions.
5 end
3 end 5 4 3 2 1 P HO A T C G OH
Remember…..
DNA strands run in opposite directions.
5’ indicates open P end
3’ indicates open -OH end
Figure 10.5B The opposite orientations of DNA strands 11

12. DNA Polymerase can only attach nucleotides to 3’-end
New strand
Template strand
5¢ end
3¢ end
5¢ end
3¢ end
Sugar
Base
Phosphate
DNA polymerase
3¢ end
3¢ end
Pyrophosphate
Nucleoside
triphosphate
5¢ end
5¢ end

13. Animation: Leading Strand Animation: Lagging Strand3
DNA polymerase molecule
This daughter strand is synthesized continuously 5
Parental DNA 5 3
Replication fork
This daughter strand is synthesized in pieces 3 5
Animation: Leading Strand 5 3
Figure 10.5C How daughter DNA strands are synthesized
Animation: Lagging Strand
DNA ligase
Overall direction of replication 13

14. Overall direction of replication
LE 16-14 3¢
Parental DNA 5¢
Leading strand 5¢ 3¢
Okazaki
fragments
Lagging strand 3¢ 5¢
DNA pol III
Template
strand
Leading strand
Lagging strand
Template
strand
DNA ligase
Overall direction of replication

15. Animation: DNA Replication Review
Overall direction of replication
Leading
strand
Lagging
strand
Origin of replication
Lagging
strand
Leading
strand
OVERVIEW
DNA polymerase
Leading
strand
DNA ligase
Replication fork 5¢
DNA polymerase 3¢
Primase
DNA
polymerase
Parental DNA
Lagging
strand
Primer 3¢ 5¢
Animation: DNA Replication Review

16. Bacteria
cultured in
medium
containing
15N
Bacteria
transferred to
medium
containing
14N
DNA sample
centrifuged
after 20 min
(after first
replication)
DNA sample
centrifuged
after 40 min
(after second
replication)
Less
dense
More
dense
First replication
Second replication
Conservative
model
Semiconservative
model