1. DNA technology has many useful applications
The Human Genome Project
The production of vaccines, cancer drugs, and pesticides
Engineered bacteria that can clean up toxic wastes

2. MICROBIAL GENETICS
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3. Viruses provided some of the earliest evidence that genes are made of DNA
Molecular biology studies how DNA serves as the molecular basis of heredity

4. 10.1 Experiments showed that DNA is the genetic material
THE STRUCTURE OF THE GENETIC MATERIAL
10.1 Experiments showed that DNA is the genetic material
The Hershey-Chase experiment showed that certain viruses reprogram host cells to produce more viruses by injecting their DNA
Head
DNA
Tail
Tail fiber
Figure 10.1A

5. Phage reproductive cycle
Phage attaches to bacterial cell.
Phage injects DNA.
Phage DNA directs host cell to make more phage DNA and protein parts. New phages assemble.
Cell lyses and releases new phages.
Figure 10.1C

6. The Hershey-Chase Experiment1
Mix radioactively labeled phages with bacteria. The phages infect the bacterial cells. 2
Agitate in a blender to separate phages outside the bacteria from the cells and their contents. 3
Centrifuge the mixture so bacteria form a pellet at the bottom of the test tube. 4
Measure the radioactivity in the pellet and liquid.
Radioactive protein
Empty protein shell
Radioactivity in liquid
Phage
Bacterium
Phage DNA
DNA
Batch 1 Radioactive protein
Centrifuge
Pellet
Radioactive DNA
Batch 2 Radioactive DNA
Centrifuge
Radioactivity in pellet
Figure 10.1B
Pellet

7. 10.18 Connection: Many viruses cause disease in animals
Many viruses have RNA, rather than DNA, as their genetic material
Example: flu viruses
Membranous envelope
RNA
Protein coat
Glycoprotein spike
Figure 10.18A

8. 10.19 Connection: Plant viruses are serious agricultural pests
Most plant viruses have RNA
Example: tobacco mosaic disease
Protein
RNA
Figure 10.19

9. 10.20 Connection: Emerging viruses threaten human health
The deadly Ebola virus causes hemorrhagic fever
Each virus is an enveloped thread of protein-coated RNA
Hantavirus is another enveloped RNA virus
Figure 10.20A, B

10. 10.17 Viral DNA may become part of the host chromosome
VIRUSES: GENES IN PACKAGES
Viral DNA may become part of the host chromosome
Phage
Attaches to cell
Bacterial chromosome
Phage DNA
Cell lyses, releasing phages
Phage injects DNA
Many cell divisions
Occasionally a prophage may leave the bacterial chromosome
LYTIC CYCLE
LYSOGENIC CYCLE
Phages assemble
Phage DNA circularizes
Lysogenic bacterium reproduces normally, replicating the prophage at each cell division
Prophage OR
New phage DNA and proteins are synthesized
Phage DNA inserts into the bacterial chromosome by recombination

11. 10.21 The AIDS virus makes DNA on an RNA template
HIV is a retrovirus
Envelope
Glycoprotein
Protein coat
RNA (two identical strands)
Reverse transcriptase
Figure 10.21A

12. Inside a cell, HIV uses its RNA as a template for making DNA to insert into the host chromosome
Viral RNA
CYTOPLASM 1
NUCLEUS
DNA strand
Chromosomal DNA 2 3
Provirus DNA
Double- stranded DNA 4 5
RNA
Viral RNA and proteins 6
Figure 10.21B

13. 10.22 Virus research and molecular genetics are intertwined
Virus studies help establish molecular genetics
Molecular genetics helps us understand viruses
such as HIV, seen here attacking a white blood cell
Figure 10.22

14. 10.19 EVOLUTION CONNECTION: Emerging viruses threaten human health
Examples of emerging viruses
HIV
Ebola virus
West Nile virus
RNA coronavirus causing severe acute respiratory syndrome (SARS)
Avian flu virus
For the Discovery Video Emerging Diseases, go to Animation and Video Files.
Student Misconceptions and Concerns
1. Students and many parents with young children expect antibiotics to be used to treat many respiratory infections, even though such infections may result from a virus. Students will benefit from a thorough explanation of why antibiotics are inappropriate for viral infections as well as the rising numbers of antibiotic-resistant bacteria that have evolved as a result of the overprescription of antibiotics.
2. The success of modern medicine has perhaps led to overconfidence in our ability to treat disease. Students often do not understand that there are few successful treatments for viral infections. Instead, the best defense against viruses is prevention, by reducing the chances of contacting the virus and the use of vaccines.
Teaching Tips
1. There is an interesting relationship between the speed at which a virus kills or debilitates a host and the extent to which it spreads from one organism to another. This is something to consider for a class discussion. Compare two viral infections. Infection A multiplies within the host, is spread by the host to other people through casual contact, but does not cause its lethal symptoms until 5–10 years after infection. Virus B kills the host within 1–2 days of infection, is easily transmitted, and causes severe symptoms within hours of contact. Which virus is likely to spread the fastest through the human population on Earth? Which might be considered the most dangerous to humans?
2. The annual mutations and variations in flu viruses require the production of a new flu vaccine every year. The Centers for Disease Control and Prevention monitors patterns of flu outbreaks, especially in Asia (where many variations of flu viruses originate). They must predict which strains are most likely to be dangerous in the coming year and then synthesize an appropriate vaccine.
Copyright © 2009 Pearson Education, Inc.

15. From E.Coli to a Map of Our Genes
Research on E. coli revealed that these bacteria have a sexual mechanism that can bring about the combining of genes from two different cells
This discovery led to the development of recombinant DNA technology
a set of techniques for combining genes from different sources

16. 10.22 Bacteria can transfer DNA in three ways
Transformation is the uptake of DNA from the surrounding environment
Transduction is gene transfer through bacteriophages
Conjugation is the transfer of DNA from a donor to a recipient bacterial cell through a cytoplasmic bridge
Recombination of the transferred DNA with the host bacterial chromosome leads to new combinations of genes
Student Misconceptions and Concerns
1. Students and many parents with young children expect antibiotics to be used to treat many respiratory infections, even though such infections may result from a virus. Students will benefit from a thorough explanation of why antibiotics are inappropriate for viral infections as well as the rising numbers of antibiotic-resistant bacteria that have evolved as a result of the overprescription of antibiotics.
2. The success of modern medicine has perhaps led to overconfidence in our ability to treat disease. Students often do not understand that there are few successful treatments for viral infections. Instead, the best defense against viruses is prevention, by reducing the chances of contacting the virus and the use of vaccines.
Teaching Tips
1. The authors note that the figures in Module represent the size of the bacterial chromosome as much smaller than they actually are. They note that a bacterial chromosome is hundreds of times longer than the cell. These chromosomes use extensive folding to fit inside the cell.
2. You might challenge students to explain why conjugation is sometimes called bacterial sex. Students might note that two organisms cooperate to produce a new, genetically unique bacterium.
Copyright © 2009 Pearson Education, Inc.

17. DNA enters cell Fragment of DNA from another bacterial cell
DNA enters
cell
Fragment of
DNA from
another
bacterial cell
Figure 10.22A Transformation.
Transformation has been proposed as a method for transferring antibiotic resistance for the ulcer-causing bacteria Helicobacter pylori, both for members within this species and between species in the Helicobacter genus. This could undermine the currently successful use of antibiotics to treat ulcers.
Bacterial chromosome
(DNA)

18. Phage Fragment of DNA from another bacterial cell (former phage host)
Phage
Fragment of
DNA from
another
bacterial cell
(former phage
host)
Figure 10.22B Transduction.
During phage infection, the bacterial chromosome becomes fragmented. Bacterial DNA molecules of a size similar to the phage DNA can be packaged into phage particles. These phage particles inject bacterial DNA into another cell, leading to a possible change in genotype for the host. Phage particles carrying bacterial DNA do not continue the infection.

19. Mating bridge Sex pili Donor cell (“male”) Recipient cell (“female”)
Mating bridge
Sex pili
Figure 10.22C Conjugation.
As described in Module 10.23, conjugation depends on a plasmid called the F factor (fertility factor) that is either separate from the chromosome in an F+ cell or integrated into the chromosome in an Hfr cell (High frequency of recombination). The F plasmid can integrate at random locations, so different Hfr cells will have the factor at a unique position on the chromosome. This figure shows conjugation for an Hfr cell. During conjugation, one strand of DNA containing a portion of the F factor and its adjacent bacterial genes is transferred to the donor. The number of bacterial genes transferred will depend on the length of time that the cytoplasmic bridge is maintained. It is unlikely that the cells would remain attached long enough to transfer the entire bacterial chromosome and all portions of the F factor. This process uses “rolling circle” replication, whereby the donor replaces the donated strand using the strand remaining in the cell as a template. Recombination is required to integrate transferred genes into the recipient cell’s chromosome.
Donor cell
(“male”)
Recipient cell
(“female”)

20. Donated DNA Crossovers Degraded DNA Recipient cell’s chromosome
Donated DNA
Crossovers
Degraded DNA
Figure 10.22D Integration of donated DNA into the recipient cell’s chromosome.
Since the bacterial chromosome is a circle, two crossovers are needed to integrate transferred genes. If there were only one crossover event, the chromosome would be opened up into a linear structure, which would be subject to nuclease digestion within the cell.
Recipient cell’s
chromosome
Recombinant
chromosome

21. 10.23 Bacterial plasmids can serve as carriers for gene transfer
Plasmids are small circular pieces of DNA separate from the main DNA of the bacteria and key tools for DNA technology
R plasmids transfer genes for antibiotic resistance by conjugation
Researchers use plasmids to insert genes into bacteria
The R plasmid has genes for sex pilus formation along with genes for antibiotic resistance.
For the BLAST Animation Plasmid, go to Animation and Video Files.
Student Misconceptions and Concerns
1. Students and many parents with young children expect antibiotics to be used to treat many respiratory infections, even though such infections may result from a virus. Students will benefit from a thorough explanation of why antibiotics are inappropriate for viral infections as well as the rising numbers of antibiotic-resistant bacteria that have evolved as a result of the overprescription of antibiotics.
2. The success of modern medicine has perhaps led to overconfidence in our ability to treat disease. Students often do not understand that there are few successful treatments for viral infections. Instead, the best defense against viruses is prevention, by reducing the chances of contacting the virus and the use of vaccines.
Teaching Tips
1. The figures in Module provide essential imagery for a detailed discussion of bacterial conjugation. The abstract details presented in Module are likely new to most of your students.
2. Module notes the possible consequences of widespread use of antibiotics. Consider asking your students to consider the value of widespread use of antibacterial soaps throughout their homes.
Copyright © 2009 Pearson Education, Inc.

22. 1 2 3 4 5 Cell containing gene of interest Bacterium Plasmid isolated
DNA
isolated 3
Gene inserted into plasmid
Bacterial chromosome
Plasmid
Gene of interest
Recombinant DNA (plasmid)
DNA 4
Plasmid put into bacterial cell
Recombinant bacterium 5
Cell multiplies with gene of interest
Copies of gene
Copies of protein
Gene for pest resistance inserted into plants
Clones of cell
Protein used to make snow form at higher temperature
Gene used to alter bacteria for cleaning up toxic waste
Protein used to dissolve blood clots in heart attack therapy
Figure 12.3

23. 12.4 Enzymes are used to “cut and paste” DNA
Restriction enzyme recognition sequence
Restriction enzymes cut DNA at specific points
DNA ligase “pastes” the DNA fragments together
The result is recombinant DNA 1
DNA
Restriction enzyme cuts the DNA into fragments
Restriction enzyme cuts the DNA into fragments 2
Sticky end
Addition of a DNA fragment from another source 3
Two (or more) fragments stick together by base-pairing 4
DNA ligase pastes the strand 5
Figure 12.4
Recombinant DNA molecule

24. 12.5 Genes can be cloned in recombinant plasmids: A closer look
Bacteria take the recombinant plasmids and reproduce
This clones the plasmids and the genes they carry
Products of the gene can then be harvested

25. Bacterial clone carrying many copies of the human gene1
Isolate DNA from two sources
Human cell
E. coli 2
Cut both DNAs with the same restriction
enzyme
Plasmid
DNA
Gene V
Sticky ends 3
Mix the DNAs; they join by base-pairing 4
Add DNA ligase to bond the DNA covalently
Recombinant DNA plasmid
Gene V 5
Put plasmid into bacterium by transformation 6
Clone the bacterium
Bacterial clone carrying many copies of the human gene
Figure 12.5

26. 12.6 Cloned genes can be stored in genomic libraries
Recombinant DNA technology allows the construction of genomic libraries
Genomic libraries are sets of DNA fragments containing all of an organism’s genes
Copies of DNA fragments can be stored in a cloned bacterial plasmid or phage
Genome cut up with restriction enzyme
Recombinant plasmid
Recombinant phage DNA OR
Phage
clone
Bacterial clone
Plasmid
library
Phage
library
Figure 12.6

27. 12.7 Reverse transcriptase helps make genes for cloning
OTHER TOOLS OF DNA TECHNOLOGY
12.7 Reverse transcriptase helps make genes for cloning
Reverse transcriptase can be used to make smaller cDNA libraries
These contain only the genes that are transcribed by a particular type of cell

28. RNA splicing (removes introns)
CELL NUCLEUS
Exon
Intron
Exon
Intron
Exon
DNA of eukaryotic gene 1
Transcription
RNA
transcript 2
RNA splicing (removes introns)
mRNA 3
Isolation of mRNA from cell and addition of reverse transcriptase; synthesis of DNA strand
TEST TUBE
Reverse transcriptase 4
Breakdown of RNA
cDNA strand 5
Synthesis of second DNA strand
cDNA of gene (no introns)
Figure 12.7

29. 12.8 Nucleic acid probes identify clones carrying specific genes
A nucleic acid probe can tag a desired gene in a library
Radioactive probe (DNA)
Mix with single- stranded DNA from various bacterial (or phage) clones
Single-stranded DNA
Base pairing indicates the gene of interest
Figure 12.8A

30. DNA probes can identify a bacterial clone carrying a specific gene
Bacterial colonies containing cloned segments of foreign DNA
Radioactive DNA 1
Transfer cells to filter
Solution containing probe
Filter paper 2
Treat cells on filter to separate DNA strands 3
Add probe to filter
Probe DNA
Gene of interest
Single-stranded DNA from cell
Hydrogen-bonding 4
Autoradiography
Colonies of living cells containing gene of interest
Developed film 5
Compare autoradiograph with master plate
Figure 12.8B
Master plate

31. This technique may revolutionize the diagnosis and treatment of cancer
12.9 Connection: DNA microarrays test for the expression of many genes at once
A labeled probe can reveal patterns of gene expression in different kinds of cells
This technique may revolutionize the diagnosis and treatment of cancer
cDNA
DNA of gene
DNA microarray, actual size (6,400 genes)
Figure 12.9