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CHAPTER 21
DNA AND BIOTECHNOLOGY
BEHAVIORAL OBJECTIVES
1. Describe the structure of DNA including the components of nucleotides, which parts of the nucleotides are
covalently bonded to form DNA, and the role of hydrogen bonds. [21.1, pp.422-423, Fig. 21.2-21.4]
2. Explain what is meant by complementary base pairing. [21.1, p.423]
3. Understand how DNA replicates. [21.1, pp.423-424, Fig. 21.5]
4. Describe the structure of RNA including the components of the monomer and which parts of the monomers are
covalently bonded to form the polymer. [21.1, p.425, Fig. 21.6]
5. List the three types of RNA found in cells and their various functions. [21.1, p.425]
6. Compare and contrast DNA and RNA structurally and functionally. [21.1, p.425, Table 21.1]
7. Describe the process of transcription and translation as components of gene expression, especially describe the
function of DNA, mRNA, tRNA, ribosomes, and necessary enzymes. [21.2, p.426, Fig. 21.8-21.12]
8. Explain the phrase “the genetic code is universal”. [21.2, p. 426, Table 21.2]
9. Understand how messenger RNA (mRNA) is processed. [21.2, pp.427-429, Fig. 21.10, 21.11]
10. Understand how the cell regulates gene expression. [21.2, p.431, Fig. 21.14, Table 21.3]
11. Describe the steps involved in the cloning of a gene. [21.3, pp.432-433, Fig. 21.15-21.16]
12. List and give examples of biotechnology products and biotechnology techniques. [21.3, pp.434-438, Fig. 21.18]
13. Discuss the importance of transgenic plants, bacteria, and animals. [21.3, pp.434-438]
14. Explain the mechanisms by which chromosomes are mapped to determine the location of specific genes. [21.3,
p.437, Fig. 21.19]
15. Describe a possible method for gene therapy in humans. [21.3, pp. 437-438, Fig. 21.20, Table 21.4]
16. Understand and use the bold-faced and italicized terms included in this chapter. [Understanding Key Terms,
p.441]
EXTENDED LECTURE OUTLINE
21.1 DNA and RNA Structure and Function
DNA is the genetic material and is found in the chromosomes of cells. When the cell is not dividing, DNA exists as
diffuse chromatin. During cell division, chromatin condenses into chromosomes.
DNA Structure and Replication
Nucleotides are composed of a phosphate, a sugar, and a base. DNA has the sugar deoxyribose and four different
bases: adenine (A), thymine (T), guanine (G), and cytosine (C). There is complementary base pairing within DNA
such that A always pairs with T, and G with C. The sugar-phosphate backbone forms the uprights of the DNA
double helix, with the base pairs comprising the rungs of the ladder-like shape.
Replication of DNA
DNA replication occurs during chromosome duplication. First, hydrogen bonds between bases break, and
enzymes “unzip” the molecule. New nucleotides move into complementary positions. New nucleotides are
joined by DNA polymerase. The new DNA molecules are complete, with each parent strand serving as a
template for a new strand. Thus, the duplication is semiconservative. A replication error persists as a
mutation.
The Structure and Function of RNA
RNA (ribonucleic acid) is a single strand of nucleotides containing the sugar ribose. The base uracil (U) replaces
thymine in RNA. RNA is a helper molecule in protein synthesis.
Ribosomal RNA
Ribosomal RNA (rRNA) is formed off a DNA template in the nucleolus. It joins with proteins imported
from the cytoplasm to form the subunits of ribosomes.
Messenger RNA
Messenger RNA (mRNA) forms off a DNA template in the nucleus and carries genetic information out to
the cytoplasm for protein synthesis.
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Transfer RNA
Transfer RNA (tRNA) forms off a DNA template in the nucleus and transfers amino acids to the
ribosomes, where protein is synthesized.
Mader VRL CD-ROM
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Image 0404l.jpg (Fig. 21.2)
Image 0405l.jpg (Fig. 21.2)
Image 0406l.jpg (Fig. 21.3)
Image 0407l.jpg (Fig. 21.4)
Image 0408l.jpg (Fig. 21.5)
Life Science Animations VRL 2.0
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Transparencies
Image 0409l.jpg (Fig. 21.6)
Principles of Inheritance/DNA As Genetic Material/ DNA is
Highly Condensed in Eukaryotic Cells
Principles of Inheritance/DNA As Genetic Material/ DNA
Packaging
Principles of Inheritance/DNA As Genetic Material/ Overview
of DNA Replication
Principles of Inheritance/DNA As Genetic Material/
Semiconservative Replication (Simplified)
Principles of Inheritance/DNA As Genetic Material/ DNA
Replication Takes Many Steps
Principles of Inheritance/DNA As Genetic Material/ DNA
Replication_1
Principles of Inheritance/DNA As Genetic Material/ DNA
Replication_2
Principles of Inheritance/DNA As Genetic Material/ DNA
Strands are Antiparallel
Principles of Inheritance/DNA As Genetic Material/DNA
Repair
Principles of Inheritance/DNA As Genetic Material/ Two Types
of DNA Repair
Genetics/DNA/DNA Structure
Genetics/DNA/DNA Replication
302 (Fig. 21.2)
303 (Fig. 21.3)
304 (Fig. 21.4)
305 (Fig. 21.5)
306 (Fig. 21.6)
21.2 Gene Expression
Genes are expressed when a protein product occurs in the cell.
Structure and Function of Proteins
Proteins are composed of building blocks called amino acids. Twenty amino acids are found in cell proteins.
Proteins differ in the number and sequence of their amino acids, which also determine the protein’s shape. Some
proteins serve structural functions, and others are enzymes.
The DNA Code
A gene is a sequence of DNA that codes for a protein. DNA contains a triplet code. The genetic code is universal
and is used by all organisms.
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Transcription
During transcription, the first of two steps of gene expression, DNA serves as a template for mRNA. RNA
polymerase joins the nucleotides. The triplet code of DNA translates to a codon of mRNA.
Processing mRNA
DNA contains exons and introns. Before mRNA leaves the nucleus, the introns are excised so that only the
exons are expressed.
Translation
During translation, the sequence of codons results in a sequence of amino acids in a protein. Translation requires
three steps. During initiation, mRNA binds to the ribosome. During elongation, the polypeptide is constructed, one
amino acid at a time. During termination, a stop-codon sequence is reached, and the ribosome falls away from the
mRNA molecule. Several ribosomes (called a polyribosome) can move along one mRNA molecule at a time.
Review of Gene Expression
DNA contains a triplet code for each amino acid. During transcription, DNA serves as a template for the formation
of mRNA which now has a certain sequence of codons. Messenger RNA is processed before it leaves the nucleus,
during which time its introns are removed. Messenger RNA leaves the nucleus and becomes associated with a
ribosome. During translation, transfer RNA molecules brings amino acids to the ribosomes and the pairing between
anticodons and codons sequences the amino acids in the order originally dictated by the sequence of bases in DNA.
The Regulation of Gene Expression
Gene expression can be controlled in the nucleus during transcription (transcriptional control) or after transcription
(posttranscriptional control) or in the cytoplasm in translational control at the ribosome or posttranslational control.
Activated Chromatin
For genes to function in cells, the chromosome must first decondense in the area to be transcribed.
Transcription Factors
DNA-binding proteins, called transcription factors, regulate gene activity during cell specialization.
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Image 0411l.jpg (Fig. 21.8)
Image 0412l.jpg (Fig. 21.9)
Image 0413l.jpg (Fig. 21.10)
Image 0414al.jpg (Fig. 21.11)
Image 0414bl.jpg (Fig. 21.11)
Image 0414cl.jpg (Fig. 21.11)
Image 0414dl.jpg (Fig. 21.11)
Image 0414el.jpg (Fig. 21.11)
Image 0415l.jpg (Fig. 21.12)
Image 0416l.jpg (Fig. 21.13)
Image 0417l.jpg (Fig. 21.14)
Life Science Animations VRL 2.0
Principles of Inheritance/Transcription and Translation/ Protein
Synthesis in Eukaryotes
Principles of Inheritance/Transcription and Translation/
Relationship Among RNA, DNA Template and DNA
Coding Strand
Principles of Inheritance/Transcription and Translation/
Transcription of RNA from DNA
Principles of Inheritance/Transcription and Translation/
Transcription_ 1
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Transcription_2
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Principles of Inheritance/Transcription and Translation/
Beginning Translation
Principles of Inheritance/Transcription and Translation/
Translating a Polypeptide
Principles of Inheritance/Transcription and Translation/ Setting
Stage for Transcription to Begin
Principles of Inheritance/Transcription and Translation/
Polyribosome
Principles of Inheritance/Transcription and Translation/
Translation_1
Principles of Inheritance/Transcription and Translation/
Translation_2
Principles of Inheritance/Transcription and Translation/
Summary of Gene Expression
Principles of Inheritance/Transcription and Translation/
Messenger RNA (mRNA) Processing in Eukaryotes
Principles of Inheritance/Control of Gene Expression/ Levels of
Gene Expression Control in Eukaryotic Cells
Principles of Inheritance/Control of Gene Expression/
Transcription Factors
Mader ESP Modules Online
Genetics/Protein Synthesis/Gene Activity
Genetics/Protein Synthesis/Transcription
Genetics/Protein Synthesis/Translation
Genetics/Protein Synthesis/Gene Regulation
Transparencies
307 (Fig. 21.7)
308 (Table 21.2)
309 (Fig. 21.8)
310 (Fig. 21.9)
311 (Fig. 21.10)
312 (Fig. 21.11)
313 (Fig. 21.12)
314 (Fig. 21.13)
315 (Table 21.3)
316 (Fig. 21.14
21.3 Biotechnology
Biotechnology uses genetic engineering to achieve the desired end. Genetic engineering allows the insertion of a
foreign gene into new cells, which are then able to produce a different product.
The Cloning of a Gene
When many copies of the same gene are obtained, the gene is said to be cloned.
Recombinant DNA Technology
Recombinant DNA contains DNA from two or more different sources. A technician selects a vector that
will provide a means of getting a gene into a host cell. Plasmids and also viruses can serve as vectors. A
restriction enzyme cleaves the plasmid DNA and foreign DNA at a specific sequence, leaving “sticky”
ends. The sticky ends allow foreign DNA to be inserted into plasmid DNA. DNA ligase seals the two types
of DNA together. Then the plasmid is put into a bacterial cell and many copies of the foreign DNA as the
bacteria reproduce.
Bacteria do not have the enzymes to process mRNA but reverse transcriptase can be used to make a DNA
copy of mature mRNA—one without introns.
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The Polymerase Chain Reaction
The polymerase chain reaction can produce millions of copies of a single gene or piece of DNA. Primers on
either side of the target DNA get the chain reaction going.
Analyzing DNA Segments
DNA can be subjected to DNA fingerprinting, that is treatment with restriction enzymes produces
fragments that form a pattern when separated according to their length. Matching patterns can identify a
criminal or the parent of a child. Patterns also help with medical diagnoses and tracing the evolution of
humans and other species.
Biotechnology Products
Transgenic organisms have had a foreign gene inserted into them.
From Bacteria
Transgenic bacteria have been used to produce biotechnology products like insulin or t-PA, promote the
health of plants, degrade wastes, produce chemicals, and help mine metals.
From Plants
Transgenic plants now produce biotechnology products like hormone, clotting factors, and antibodies.
Some plants have been enhanced to resist pests and herbicides.
From Animals
Gene pharming is the use of trangenic farm animals to produce pharmaceuticals in the milk of females.
There are plans to use animals to produce drugs for the treatment of cystic fibrosis, cancer, blood diseases
and so forth.
Cloning of Transgenic Animals
Cloning of animals is now a reality. A diploid nucleus from bioengineered animal is inserted into
enucleated eggs from a donor. These eggs are inserted into the uterus and when development is finished the
surrogate mother gives birth to the cloned animals.
The Human Genome Project
The Human Genome Project has two goals: to know the sequence of genes on all the human chromosomes and to
know the sequence of bases on all the human chromosomes. Then, we might be able to determine the genetic defects
of individuals and give them proper treatment for any ills they might have. It used to be that the Human Genome
Project was done by government sponsored labs but now pharmaceuticals companies want to sponsor specific
researchers because they hope to get a head start on possible drug remedies for various genetic illnesses.
Gene Therapy
Gene therapy is the insertion of genetic material into human cells for the treatment of a disorder.
Genetic Disorders
Bone marrow stem cells are withdrawn from the body, a retrovirus is used to insert a normal gene into
them, and the stem cells are returned to the body. This method of gene therapy is still experimental.
There are plans to treat patients with hypercholesterolemia and cystic fibrosis.
Other Illnesses
Gene therapy may help produce a growth factor to help form new blood vessels during angioplasty. In vivo
gene therapy may one day cure hemophilia, diabetes, Parkinson disease and AIDS.
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Image 0418al.jpg (Fig. 21.15)
Image 0418bl.jpg (Fig. 21.15)
Image 0418cl.jpg (Fig. 21.15)
Image 0419l.jpg (Fig. TA21.1)
Image 0420l.jpg (Fig. 21.16)
Image 0421al.jpg (Fig. 21.17)
Image 0421bl.jpg (Fig. 21A)
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Image 0425l.jpg (Fig. 21B)
Life Science Animations VRL 2.0
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Case Studies Online
Transparencies
Image 0426l.jpg (Fig. TA21.2)
Principles of Inheritance/Biotechnology/ Cloning of a Gene
Principles of Inheritance/Biotechnology/ Amplifying Specific
DNA Sequence
Principles of Inheritance/Biotechnology/ Polymerase Chain
Reaction
Principles of Inheritance/Biotechnology/PCR
Principles of Inheritance/Biotechnology/ Preparation of a
Genomic Library
Principles of Inheritance/Biotechnology/ Ex Vivo Gene Therapy
in Humans
Genetics/Recombinant DNA/Technology
Genetics/Recombinant DNA/Applications
DNA Dragnets
Transgenic Cotton Tested in India; Farmers Fear Introduction of
Terminator Crops
Getting Recombinant Proteins Straight from the Roots
Genetically Altered Papayas Save the Harvest
317 (Fig. 21.15)
318 (Fig. TA21.1)
319 (Fig. 21.16)
320 (Fig. 21.18)
321 (Fig. 21.19)
322 (Fig. 21.20)
323 (Fig. TA21.2)
SEVENTH EDITION CHANGES
New/Revised Text:
This was chapter 20 in the previous edition. Most main sections and topics were rewritten for clarity.
21.1 DNA and RNA Structure and Function. Most topics in this section were rewritten for clarity.
21.2 Gene Expression. The DNA Code and Transcription topics were rewritten for clarity.
21.3 Biotechnology. Polymerase Chain Reaction was rewritten for clarity. Cloning of Transgenic Animals
was updated, and the diagram (Fig. 21.18) that illustrates this procedure has been simplified for better
understanding. The Human Genome Project discussion was updated to include recent achievements in that area.
Gene sequencing of diseases or afflictions found on chromosome 17 is illustrated in new Figure 21.19. The Gene
Therapy discussion has been updated and greatly expanded. It gives new information on gene therapy treatments for
cystic fibrosis and for children with SCID using bone marrow stem cells. It also discussed the possibilities for the
use of gene therapy to treat other illnesses, such as hemophilia, AIDS, cancer, and heart disease.
New Health Focus: Organs for Transplant
New Bioethical Focus: Transgenic Plants
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New/Revised Figures:
21.2 DNA location and structure; 21.9 Function of introns; 21.16 Polymerase chain reaction; 21.18
Genetically engineered animals; 21.19 Genetic map of chromosome 17; Colors have been made consistent in all
DNA/RNA illustrations.
New/Revised Tables:
21.2 Some DNA Codes and RNA Codons has been expanded.
STUDENT ACTIVITIES
Xenotransplantation
1. Scientists have begun genetically engineering pigs to serve as organ donors for humans who need transplants.
They are gradually making the organs less antigenic to humans. The main concern is that even so pig’s organs
might carry animal viruses into humans. (HIV is a virus that jumped from monkeys into humans.) Have
students read the Health Focus “Organs for Transplant”. Discuss some of the fears brought out in the article.
General Public’s Understanding of Biotechnology
2. Students should read the Bioethical Focus, “Transgenic Plants,” before coming to class. Divide the class into
groups. Each group is to prepare a list of true-false questions concerning biotechnology, and transgenic plants in
particular. Ask student volunteers to type out the list and “test” their friends, family, and other students on
campus. They should then report back on the public’s general level of understanding about biotechnology.
The Promise of Biotechnology
3. Ask students to read “Introduction: The Biotech Century” (Time, January 11, 1999, page 42). Then have them
read Leon Jaroff’s “Fixing the Genes” (pp.68-73) making sure they also read the sidebar article on pp.72-73
titled “Success Stories”). [Ask the library to hold this issue on reserve or make copies of these articles for your
students to use.] Use these to generate a discussion on gene therapy, its future and our concerns.
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