12 lecture presentation0

Biology and Society:
DNA, Guilt, and Innocence
• DNA profiling is the analysis of DNA samples that can be used to
determine whether the samples come from the same individual.
• DNA profiling can therefore be used in courts to indicate if
someone is:
– Guilty
– Innocent
© 2010 Pearson Education, Inc.

• DNA technology has led to other advances in the:
– Creation of genetically modified crops
– Identification and treatment of genetic diseases

• Biotechnology today means the use of DNA technology, methods
for:
– Studying and manipulating genetic material
– Modifying specific genes
– Moving genes between organisms

• Recombinant DNA is formed when scientists combine
nucleotide sequences (pieces of DNA) from two different sources
to form a single DNA molecule.
• Recombinant DNA technology is widely used in genetic
engineering, the direct manipulation of genes for practical
purposes.

Applications: From Humulin to Foods to
“Pharm” Animals
• By transferring the gene for a desired protein into a bacterium or
yeast, proteins that are naturally present in only small amounts
can be produced in large quantities.

Making Humulin
• In 1982, the world’s first genetically engineered pharmaceutical
product was sold.
• Humulin, human insulin:
– Was produced by genetically modified bacteria
– Was the first recombinant DNA drug approved by the FDA
– Is used today by more than 4 million people with diabetes

• Today, humulin is continuously produced in gigantic
fermentation vats filled with a liquid culture of bacteria.

• DNA technology is used to produce medically valuable
molecules, including:
– Human growth hormone (HGH)
– The hormone EPO, which stimulates production of red blood cells
– Vaccines, harmless variants or derivatives of a pathogen used to prevent
infectious diseases

Genetically Modified (GM) Foods
• Today, DNA technology is quickly replacing traditional plant-
breeding programs.
• Scientists have produced many types of genetically modified
(GM) organisms, organisms that have acquired one or more
genes by artificial means.
• A transgenic organism contains a gene from another organism,
typically of another species.

• In the United States today, roughly one-half of the corn crop and
over three-quarters of the soybean and cotton crops are
genetically modified.
• Corn has been genetically modified to resist insect infestation.

• “Golden rice” has been genetically modified to produce beta-
carotene used in our bodies to make vitamin A.

• DNA technology:
– May eventually replace traditional animal breeding but
– Is not currently used to produce transgenic animals sold as food
• Meat may come from livestock that receive genes that produce:
– Larger muscles or
– Healthy omega-3 fatty acids instead of less healthy fatty acids (already
done in 2006 in pigs)

Recombinant DNA Techniques
• Bacteria are the workhorses of modern biotechnology.
• To work with genes in the laboratory, biologists often use
bacterial plasmids, small, circular DNA molecules that are
separate from the much larger bacterial chromosome.

Plasmids
Bacterial
chromosome
Remnant of
bacterium
ColorizedTEM
Figure 12.7

• Plasmids:
– Can easily incorporate foreign DNA
– Are readily taken up by bacterial cells
– Can act as vectors, DNA carriers that move genes from one cell to
another
– Are ideal for gene cloning, the production of multiple identical copies of
a gene-carrying piece of DNA

• Recombinant DNA techniques can help biologists produce large
quantities of a desired protein.
Blast Animation: Genetic Recombination in Bacteria
Animation: Cloning a Gene

Plasmid
Bacterial cell
Isolate
plasmids.
Some uses
of genes
Gene for pest
resistance
Gene for
toxic-cleanup
bacteria
Genes may be
inserted into
other organisms.
Find the clone with
the gene of interest.
The gene and protein
of interest are isolated
from the bacteria.
Clone the bacteria.
Recombinant bacteriaBacterial clone
Gene of interest
Recombinant DNA plasmids
Bacteria take up recombinant plasmids.
Harvested
proteins may be
used directly.
Some uses
of proteins
Protein for
“stone-washing”
jeans
DNA
Cell containing
the gene of interest
Protein for
dissolving
clots
Isolate
DNA.
DNA fragments
from cell
Cut both DNAs
with same
enzyme.
Gene of
interest
Other
genes
Mix the DNAs and
join them together.
Figure 12.8-8

A Closer Look: Cutting and Pasting DNA with
Restriction Enzymes
• Recombinant DNA is produced by combining two ingredients:
– A bacterial plasmid
– The gene of interest
• To combine these ingredients, a piece of DNA must be spliced
into a plasmid.

• This splicing process can be accomplished by:
– Using restriction enzymes, which cut DNA at specific nucleotide
sequences, and
– Producing pieces of DNA called restriction fragments with “sticky
ends” important for joining DNA from different sources
• DNA ligase connects the DNA pieces into continuous strands by
forming bonds between adjacent nucleotides.
Animation: Restriction Enzymes

Recognition sequence
for a restriction enzyme
Restriction
enzyme
Sticky
end
Sticky
end
DNA
A restriction enzyme cuts
the DNA into fragments.
Figure 12.9-1

Restriction
enzyme
Sticky
end
Sticky
end
DNA
A DNA fragment is added
from another source.
Figure 12.9-2

Restriction
enzyme
Sticky
end
Sticky
end
DNA
Fragments stick together by
base pairing.
Figure 12.9-3

Restriction
enzyme
Sticky
end
Sticky
end
DNA
DNA
ligase
Recombinant DNA molecule
Fragments stick together by
base pairing.
DNA ligase joins the
fragments into strands.
Figure 12.9-4

DNA PROFILING AND FORENSIC SCIENCE
• DNA profiling:
– Can be used to determine if two samples of genetic material are from a
particular individual
– Has rapidly revolutionized the field of forensics, the scientific analysis of
evidence from crime scenes
• To produce a DNA profile, scientists compare genetic markers,
sequences in the genome that vary from person to person.
Video: Biotechnology Lab

DNA isolated
Crime scene Suspect 1 Suspect 2
Figure 12.13-1

DNA isolated
DNA amplified
Figure 12.13-2

DNA isolated
DNA amplified
DNA compared
Figure 12.13-3

Investigating Murder, Paternity etc.
• DNA profiling can be used to:
– Test the guilt of suspected criminals
– Identify tissue samples of victims
– Resolve paternity cases
– Identify contraband animal products

DNA Profiling Techniques
The Polymerase Chain Reaction (PCR)
• The polymerase chain reaction (PCR):
– Is a technique to copy quickly and precisely any segment of DNA and
– Can generate enough DNA, from even minute amounts of blood or other
tissue, to allow DNA profiling

Initial
DNA
segment
Number of DNA molecules
1 2 4 8
Figure 12.15

Short Tandem Repeat (STR) Analysis
• How do you test if two samples of DNA come from the same
person?
• Repetitive DNA:
– Makes up much of the DNA that lies between genes in humans and
– Consists of nucleotide sequences that are present in multiple copies in the
genome

• Short tandem repeats (STRs) are:
– Short sequences of DNA
– Repeated many times, tandemly (one after another), in the genome
• STR analysis:
– Is a method of DNA profiling
– Compares the lengths of STR sequences at certain sites in the genome
Blast Animation: DNA Fingerprinting

Crime scene DNA
Suspect’s DNA
Same number of
short tandem repeats
Different numbers of
short tandem repeats
STR site 1 STR site 2
AGAT
AGAT GATA
GATA
Figure 12.16

Gel Electrophoresis
• STR analysis:
– Compares the lengths of DNA fragments
– Uses gel electrophoresis, a method for sorting macromolecules—usually
proteins or nucleic acids—primarily by their
– Electrical charge
– Size
Blast Animation: Gel Electrophoresis

Mixture of DNA
fragments of
different sizes
Power
source
Gel
Figure 12.17-1

Mixture of DNA
fragments of
different sizes
Power
source
Gel
Figure 12.17-2

Mixture of DNA
fragments of
different sizes
Power
source
Gel
Completed gel
Band of
longest
(slowest)
fragments
Band of
shortest
(fastest)
fragments
Figure 12.17-3

• The DNA fragments are visualized as “bands” on the gel.
• The differences in the locations of the bands reflect the different
lengths of the DNA fragments.

Amplified
crime scene
DNA
Amplified
suspect’s
DNA
Longer
fragments
Shorter
fragments
Figure 12.18

GENOMICS AND PROTEOMICS
• Genomics is the science of studying complete sets of genes
(genomes).
– The first targets of genomics were bacteria.
– As of 2009, the genomes of nearly one thousand species have been
published, including:
– Mice
– Fruit flies

The Human Genome Project
• Begun in 1990, the Human Genome Project was a massive
scientific endeavor:
– To determine the nucleotide sequence of all the DNA in the human
genome and
– To identify the location and sequence of every gene

• At the completion of the project in 2004:
– Over 99% of the genome had been determined to 99.999% accuracy
– 3.2 billion nucleotide pairs were identified
– About 21,000 genes were found
– About 98% of the human DNA was identified as noncoding

• The Human Genome Project can help map the genes for specific
diseases such as:
– Alzheimer’s disease
– Parkinson’s disease

HUMAN GENE THERAPY
• Human gene therapy:
– Is a recombinant DNA procedure
– Seeks to treat disease by altering the genes of the afflicted person
– Often replaces or supplements the mutant version of a gene with a
properly functioning one

Normal human
gene isolated
and cloned
Healthy person
Figure 12.24-1

Normal human
gene isolated
and cloned
Normal human
gene inserted
into virus
Healthy person
Harmless
virus (vector)
Virus containing
normal human gene
Figure 12.24-2

Normal human
gene isolated
and cloned
Normal human
gene inserted
into virus
Virus injected
into patient with
abnormal gene
Healthy person
Harmless
virus (vector)
Virus containing
normal human gene
Bone
marrow
Bone of person
with disease
Figure 12.24-3

SAFETY AND ETHICAL ISSUES
• As soon as scientists realized the power of DNA technology, they
began to worry about potential dangers such as the:
– Creation of hazardous new pathogens
– Transfer of cancer genes into infectious bacteria and viruses

• Strict laboratory safety procedures have been designed to:
– Protect researchers from infection by engineered microbes
– Prevent microbes from accidentally leaving the laboratory

The Controversy over Genetically Modified
Foods
• GM strains account for a significant percentage of several
agricultural crops in the United States.

• Advocates of a cautious approach are concerned that:
– Crops carrying genes from other species might harm the environment
– GM foods could be hazardous to human health
– Transgenic plants might pass their genes to close relatives in nearby wild
areas

• In 2000, negotiators from 130 countries (including the United
States) agreed on a Biosafety Protocol that:
– Requires exporters to identify GM organisms present in bulk food
shipments

• In the United States, all projects are evaluated for potential risks
by a number of regulatory agencies, including the:
– Food and Drug Administration
– Environmental Protection Agency
– National Institutes of Health
– Department of Agriculture

Ethical Questions Raised by DNA Technology
• DNA technology raises legal and ethical questions—few of
which have clear answers.
– Should genetically engineered human growth hormone be used to
stimulate growth in HGH-deficient children?
– Do we have any right to alter an organism’s genes—or to create new
organisms?
– Should we try to eliminate genetic defects in our children and their
descendants?
– Should people use mail-in kits that can tell healthy people their relative
risk of developing various diseases?

• DNA technologies raise many complex issues that have no easy
answers.
• We as a society and as individuals must become educated about
DNA technologies to address the ethical questions raised by their
use.

Evolution Connection:
Profiling the Y Chromosome
• Barring mutations, the human Y chromosome passes essentially
intact from father to son.
• By comparing Y DNA, researchers can learn about the ancestry
of human males.

DNA
Polymerase chain
reaction (PCR)
amplifies STR
sites
Longer
DNA
fragments
Shorter
DNA
fragments
DNA fragments compared by gel electrophoresis
Gel
Figure 12.UN2

Normal
human gene
Virus
Bone
marrow
Normal human gene is transcribed
and translated in patient, potentially
curing genetic disease permanently
Figure 12.UN3

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