1. Chapter 20
Biotechnology

2. Overview: The DNA Toolbox
Sequencing of the human genome was completed by 2007
DNA sequencing has depended on advances in technology, starting with making recombinant DNA
In recombinant DNA, nucleotide sequences from two different sources, often two species, are combined in vitro into the same DNA molecule

3. DNA Cloning and Its Applications: A Preview
Most methods for cloning pieces of DNA in the laboratory share general features, such as the use of bacteria and their plasmids
Plasmids are small circular DNA molecules that replicate separately from the bacterial chromosome
Cloned genes are useful for making copies of a particular gene and producing a protein product

4. Gene cloning involves using bacteria to make multiple copies of a gene
Foreign DNA is inserted into a plasmid, and the recombinant plasmid is inserted into a bacterial cell
Reproduction in the bacterial cell results in cloning of the plasmid including the foreign DNA
This results in the production of multiple copies of a single gene

5. Figure 20.2 A preview of gene cloning and some uses of cloned genes
Cell containing gene of interest
Bacterium 1
Gene inserted into plasmid
Bacterial chromosome
Plasmid
Gene of interest
Recombinant DNA (plasmid)
DNA of chromosome 2
Plasmid put into bacterial cell
Recombinant bacterium 3
Host cell grown in culture to form a clone of cells containing the “cloned” gene of interest
Gene of Interest
Protein expressed by gene of interest
Copies of gene
Protein harvested
Figure 20.2 A preview of gene cloning and some uses of cloned genes 4
Basic research and various applications
Basic research on gene
Basic research on protein
Gene for pest resistance inserted into plants
Gene used to alter bacteria for cleaning up toxic waste
Protein dissolves blood clots in heart attack therapy
Human growth hor- mone treats stunted growth

6. Using Restriction Enzymes to Make Recombinant DNA
Bacterial restriction enzymes cut DNA molecules at specific DNA sequences called restriction sites
A restriction enzyme usually makes many cuts, yielding restriction fragments
The most useful restriction enzymes cut DNA in a staggered way, producing fragments with “sticky ends” that bond with complementary sticky ends of other fragments
Animation: Restriction Enzymes

7. DNA ligase is an enzyme that seals the bonds between restriction fragments

8. Restriction enzyme cuts sugar-phosphate backbones.
Fig
Restriction site
DNA 5 3 3 5 1
Restriction enzyme cuts sugar-phosphate backbones.
Sticky end 2
DNA fragment added from another molecule cut by same enzyme. Base pairing occurs.
Figure 20.3 Using a restriction enzyme and DNA ligase to make recombinant DNA
One possible combination 3
DNA ligase seals strands.
Recombinant DNA molecule

9. For example, if the desired gene is
A probe can be synthesized that is complementary to the gene of interest
For example, if the desired gene is
– Then we would synthesize this probe … … 5 G G C T A A C T T A G C 3 3 C C G A T T G A A T C G 5

10. The DNA probe can be used to screen a large number of clones simultaneously for the gene of interest
Once identified, the clone carrying the gene of interest can be cultured

11. Radioactively labeled probe molecules
Fig. 20-7
TECHNIQUE
Radioactively labeled probe molecules
Probe DNA
Gene of interest
Multiwell plates holding library
clones
Single-stranded DNA from cell
Film •
Figure 20.7 Detecting a specific DNA sequence by hybridizing with a nucleic acid probe
Nylon membrane
Nylon membrane
Location of DNA with the complementary sequence

12. Expressing Cloned Eukaryotic Genes
After a gene has been cloned, its protein product can be produced in larger amounts for research
Cloned genes can be expressed as protein in either bacterial or eukaryotic cells

13. Amplifying DNA in Vitro: The Polymerase Chain Reaction (PCR)
The polymerase chain reaction, PCR, can produce many copies of a specific target segment of DNA
A three-step cycle—heating, cooling, and replication—brings about a chain reaction that produces an exponentially growing population of identical DNA molecules

14. molecules; 2 molecules (in white boxes) match target sequence
Fig. 20-8
TECHNIQUE 5 3
Target sequence
Genomic DNA 3 5 1
Denaturation 5 3 3 5 2
Annealing
Cycle 1 yields 2
molecules
Primers 3
Extension
New nucleo- tides
Figure 20.8 The polymerase chain reaction (PCR)
Cycle 2 yields 4
molecules
Cycle 3 yields 8
molecules; 2 molecules (in white boxes) match target sequence

15. Gel Electrophoresis and Southern Blotting
One indirect method of rapidly analyzing and comparing genomes is gel electrophoresis
This technique uses a gel as a molecular sieve to separate nucleic acids or proteins by size
A current is applied that causes charged molecules to move through the gel
Molecules are sorted into “bands” by their size
Video: Biotechnology Lab

16. Figure 20.9 Gel electrophoresis
TECHNIQUE
Mixture of DNA mol- ecules of different sizes
Power source –
Cathode
Anode +
Gel 1
Power source – +
Longer molecules 2
Shorter molecules
RESULTS
Figure 20.9 Gel electrophoresis

17. In restriction fragment analysis, DNA fragments produced by restriction enzyme digestion of a DNA molecule are sorted by gel electrophoresis
Restriction fragment analysis is useful for comparing two different DNA molecules, such as two alleles for a gene
The procedure is also used to prepare pure samples of individual fragments

18. Fig
Normal -globin allele
Normal allele
Sickle-cell allele
175 bp
201 bp
Large fragment
DdeI
DdeI
DdeI
DdeI
Large fragment
Sickle-cell mutant -globin allele
376 bp
201 bp 175 bp
376 bp
Large fragment
DdeI
Figure Using restriction fragment analysis to distinguish the normal and sickle-cell alleles of the β-globin gene
DdeI
DdeI
(a) DdeI restriction sites in normal and sickle-cell alleles of -globin gene
(b) Electrophoresis of restriction fragments from normal and sickle-cell alleles

19. Reverse transcriptase-polymerase chain reaction (RT-PCR) is quicker and more sensitive
Reverse transcriptase is added to mRNA to make cDNA, which serves as a template for PCR amplification of the gene of interest
The products are run on a gel and the mRNA of interest identified

20. TECHNIQUE 1 cDNA synthesis mRNAs cDNAs Primers 2 -globin gene 3
Fig
TECHNIQUE 1
cDNA synthesis
mRNAs
cDNAs
Primers 2
PCR amplification
-globin gene 3
Gel electrophoresis
Figure RT-PCR analysis of expression of single genes
Embryonic stages
RESULTS

21. In situ hybridization uses fluorescent dyes attached to probes to identify the location of specific mRNAs in place in the intact organism

22. Fig
Figure Determining where genes are expressed by in situ hybridization analysis
50 µm

23. TECHNIQUE RESULTS Mammary cell donor Egg cell donor
Fig
TECHNIQUE
Mammary cell donor
Egg cell donor 1 2
Egg cell from ovary
Nucleus removed
Cultured mammary cells 3
Cells fused 3
Nucleus from mammary cell 4
Grown in culture
Early embryo
Figure Reproductive cloning of a mammal by nuclear transplantation
For the Discovery Video Cloning, go to Animation and Video Files. 5
Implanted in uterus of a third sheep
Surrogate mother 6
Embryonic development
Lamb (“Dolly”) genetically identical to mammary cell donor
RESULTS

24. Stem Cells of Animals
A stem cell is a relatively unspecialized cell that can reproduce itself indefinitely and differentiate into specialized cells of one or more types
Stem cells isolated from early embryos at the blastocyst stage are called embryonic stem cells; these are able to differentiate into all cell types
The adult body also has stem cells, which replace nonreproducing specialized cells

25. From bone marrow in this example
Fig
Embryonic stem cells
Adult stem cells
Early human embryo at blastocyst stage (mammalian equiva- lent of blastula)
From bone marrow in this example
Cells generating all embryonic cell types
Cells generating some cell types
Cultured stem cells
Different culture conditions
Figure Working with stem cells
Different types of differentiated cells
Liver cells
Nerve cells
Blood cells

26. Fig
(a)
This photo shows Earl Washington just before his release in 2001, after 17 years in prison.
Source of sample
STR marker 1
STR marker 2
STR marker 3
Figure STR analysis used to release an innocent man from prison
For the Discovery Video DNA Forensics, go to Animation and Video Files.
Semen on victim
17, 19
13, 16
12, 12
Earl Washington
16, 18
14, 15
11, 12
Kenneth Tinsley
17, 19
13, 16
12, 12
(b)
These and other STR data exonerated Washington and led Tinsley to plead guilty to the murder.

27. Environmental Cleanup
Genetic engineering can be used to modify the metabolism of microorganisms
Some modified microorganisms can be used to extract minerals from the environment or degrade potentially toxic waste materials
Biofuels make use of crops such as corn, soybeans, and cassava to replace fossil fuels

28. Most public concern about possible hazards centers on genetically modified (GM) organisms used as food
Some are concerned about the creation of “super weeds” from the transfer of genes from GM crops to their wild relatives

29. DNA fragments from genomic DNA or cDNA or copy of DNA obtained by PCR
Fig. 20-UN3
DNA fragments from genomic DNA or cDNA or copy of DNA obtained by PCR
Vector
Cut by same restriction enzyme, mixed, and ligated
Recombinant DNA plasmids

30. TCCATGAATTCTAAAGCGCTTATGAATTCACGGC AGGTACTTAAGATTTCGCGAATACTTAAGTGCCG
Fig. 20-UN4 5
TCCATGAATTCTAAAGCGCTTATGAATTCACGGC 3 3
AGGTACTTAAGATTTCGCGAATACTTAAGTGCCG 5
Aardvark DNA G A A T T C T T A C A G
Plasmid

31. Fig. 20-UN7