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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

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• 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

Figure 12.2


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

Figure 12.3


• 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.

Figure 12.4


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

Figure 12.5


• 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

Bacterialchromosome

Remnant ofbacterium

Col

oriz

ed T

EM

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

Isolateplasmids.

Some usesof genes

Gene for pestresistance

Gene fortoxic-cleanupbacteria

Genes may beinserted intoother organisms.

Find the clone withthe gene of interest.

The gene and proteinof interest are isolatedfrom the bacteria.

Clone the bacteria.

Recombinant bacteriaBacterial clone

Gene of interest

Recombinant DNA plasmids

Bacteria take up recombinant plasmids.

Harvestedproteins may beused directly.

Some usesof proteins

Protein for“stone-washing”jeans

DNA

Cell containingthe gene of interest

Protein fordissolvingclots

IsolateDNA.

DNA fragmentsfrom cell

Cut both DNAswith sameenzyme.

Gene ofinterest

Othergenes

Mix the DNAs andjoin 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 sequencefor a restriction enzyme

Restrictionenzyme

Sticky

end

Stickyend

DNA

A restriction enzyme cutsthe DNA into fragments.

Figure 12.9-1


Restrictionenzyme

Sticky

end

Stickyend

DNA

A DNA fragment is addedfrom another source.


Figure 12.9-2


Restrictionenzyme

Sticky

end

Stickyend

DNA



Fragments stick together bybase pairing.

Figure 12.9-3


Restrictionenzyme

Sticky

end

Stickyend

DNA

DNAligase

Recombinant DNA molecule



Fragments stick together bybase pairing.

DNA ligase joins thefragments into strands.

Figure 12.9-4

Figure 12.12


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


InitialDNAsegment

Number of DNA molecules1 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 ofshort tandem repeats

Different numbers ofshort 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 DNAfragments ofdifferent sizes

Powersource

Gel

Figure 12.17-1


Powersource

Gel

Figure 12.17-2


Powersource

Gel

Completed gel

Band oflongest(slowest)fragments

Band ofshortest(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.

Amplifiedcrime sceneDNA

Amplifiedsuspect’sDNA

Longerfragments

Shorterfragments

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

Table 12.1


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

Figure 12.20


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 humangene isolatedand cloned

Healthy person

Figure 12.24-1


Normal humangene insertedinto virus

Healthy person

Harmlessvirus (vector)

Virus containingnormal human gene

Figure 12.24-2


Normal humangene insertedinto virus

Virus injectedinto patient withabnormal gene

Healthy person

Harmlessvirus (vector)

Virus containingnormal human gene

Bonemarrow

Bone of personwith 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

Figure 12.25


The Controversy over Genetically Modified Foods• GM strains account for a significant percentage of several

agricultural crops in the United States.

Figure 12.26


• 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?

Figure 12.27


• 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 chainreaction (PCR)amplifies STRsites

LongerDNAfragments

ShorterDNAfragments

DNA fragments compared by gel electrophoresis

Gel

Figure 12.UN2

Normalhuman gene

Virus

Bonemarrow

Normal human gene is transcribedand translated in patient, potentiallycuring genetic disease permanently

Figure 12.UN3

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