bio 3201 unit 2b pink

Genetic engineering

Working in a laboratory, researchers can manipulate genetic material to alter genes and blend

plant, animal, and bacterial DNA—a process known as genetic engineering.

Recombinant DNA

A molecule of DNA that includes genetic material from different sources is called recombinant

DNA. Genetic researchers use different tools to produce and analyze recombinant DNA.

How is it done?

Restriction enzymes catalyze the cleavage of DNA at specific nucleotide sequences.

Many different restriction enzymes have been isolated, and each recognizes a different target

sequence.

Two characteristics of restriction enzymes that make them useful to genetic researchers are:

• Specificity: The cuts made are specific and predictable. That is, the same enzyme will cut a

particular strand of DNA the same way each time, producing an identical set of small DNA

fragments.

• Staggered cuts: Most produce a staggered cut that leaves a few unpaired nucleotides on a

single strand at each end of the restriction fragment. These short strands, often referred to as

sticky ends, can then form base pairs with other short strands that have a complementary

sequence. DNA ligase, joins them together. The result is a stable recombinant DNA molecule.

For example, the human insulin gene can be combined with a type of bacterial DNA called a

plasmid. The recombinant DNA molecule can be introduced into bacteria where it will replicate

numerous times and produce the human insulin protein, which can then be isolated and used

medicinally.

Polymerase Chain Reaction

In order to analyze a DNA sample, there must be a sufficient quantity of it. This means that the

DNA must be copied many times to produce a large number of identical DNA molecules. One

way this can be done is by an automated process called polymerase chain reaction, or PCR.

PCR is rapid, inexpensive and simple and it does not require the use of radioisotopes or toxic

chemicals

 DNA fragments are heated at high temperatures, which reduce the DNA double helix to

single strands. These strands become accessible to primers

 The reaction mixture is cooled down.

 Primers stick to the complementary regions in the DNA template strands, and double

strands are formed again between primers and complementary sequences

 The DNA polymerase synthesizes a complementary strand. The enzyme reads the

opposing strand sequence and extends the primers by adding nucleotides in the order in

which they can pair. The whole process is repeated over and over creating more of the

same sample of DNA.

Sorting and Analyzing DNA- Gel Electrophoresis

An important tool for analyzing DNA is gel electrophoresis. Gel electrophoresis is used to

separate molecules according to their mass and charge. It is used to separate fragments of DNA

according to their sizes.

1. To begin, a solution that contains DNA fragments is applied at one end of a gel.

2. An electric current is then passed through the gel. This causes one end of the gel to

develop a positive electric charge and the other end to develop a negative electric

charge.

3. Because DNA has a negative charge, the DNA fragments tend to move toward the gel’s

positive end. The smaller fragments move more quickly.

4. After a period of time, the fragments separate into a pattern of bands.

Together, restriction enzymes and gel electrophoresis help researchers analyze and compare

DNA samples. DNA can be cut with a restriction enzyme and run on a gel to create a DNA

fingerprint. Since no two people (other than identical twins) have the same DNA, a person’s

DNA fingerprint is unique and can be used for identification purposes.

Gathering and Managing Genetic Information- DNA Microarray

One of the most important tools in the development of genetic engineering has been

computers that are capable of handling the enormous amounts of information encoded in a

eukaryotic genome. A DNA microarray is a chip that contains a grid of thousands of microscopic

cells. Each cell contains a nucleic acid sequence that can bind with one of the mRNA molecules

transcribed during gene expression. A DNA microarray allows scientists to analyze the activity

of thousands of genes at once. For example, a microarray can be used to compare the genes

expressed by the same cell in different environments, or to compare the genes expressed by

healthy and cancerous cells.

CRISPR

An exciting new technology called CRISPR (pronounced “crisper”) promises to have a significant

impact in the field of research involving adding, deleting, or altering specific sequences in the

genome. CRISPR stands for Clustered Regularly Interspaced Short Palindromic Repeats, which is

a system that forms the basis for genome editing technology. In the field of genome

engineering, the term “CRISPR” can be programmed to target specific stretches of genetic code

and to edit DNA at precise locations. With these systems, researchers can permanently modify

genes in living cells and organisms and, in the future, may make it possible to correct mutations

at precise locations in the human genome in order to treat genetic causes of disease.

Biotechnology is the use of natural biological systems to create new technologies and products.

Few sciences have as much potential as biotechnology to change the way we live—from the

way we diagnose and treat diseases to the food we eat, the industries we work in, the air we

breathe, and even the way we define life itself. Few technologies raise as broad a range of

challenging social, ethical, and legal questions. Genetic engineering is one of the fastest-

growing areas of biotechnology.

Biotechnology Products

Genetic engineers have refined techniques for importing foreign DNA into plants and animals.

The result of a procedure like this is a transgenic organism. A transgenic organism, is an

organism whose genetic material includes DNA from a different species.

Medicinal Bacteria: In 1982, human insulin synthesized by transgenic bacteria was approved for

medical use in the United States.

Bioremediation: Genetically modified bacteria can support human health in other ways, as

well. Some bacteria naturally degrade toxic substances, such as polychlorinated biphenyls

(PCBs). Genetic engineering can enhance these metabolic functions, creating colonies of

bacteria that can be used to clean up soils polluted with PCBs. The use of living cells for

environmental remediation is known as bioremediation.

Other examples of bioremediation include bacteria that have been designed to clean up oil

spills, to filter air from factory smokestacks, or to remove heavy metals from water.

Transgenic Plants: Crop plants that contain recombinant DNA now account for over half the

corn and canola produced in North America. Many of these plants have been modified to

increase their resistance to herbicides, insect pests, or viruses. Genetic engineering has made it

possible for crops to be grown in new places, as well, by creating transgenic plants that are

tolerant of drought or that can be grown in colder climates but perhaps more importantly, in

the production of plants with increased nutrition value.

Swiss researchers developed a genetically modified strain of rice known as golden rice. This rice

has been genetically engineered to increase its iron and vitamin A content. Golden rice is now

available as a staple part of the food aid delivered to many developing countries.

Cloned and Transgenic Animals

Organisms that are genetically identical are said to be clones of one another. Since the

“invention” of Dolly, researchers have successfully used similar techniques to clone other

mammals.

Cloned offspring suffer from a high mortality rate, however, as well as a high incidence of

disease. Other forms of animal genetic engineering have been more successful.

Researchers have been able to create new varieties of animals with useful traits. For example,

transgenic milk-producing animals, such as goats, are being used to produce pharmaceutical

products. Similar steps have been used by a Canadian research company to insert a spider gene

into goats. The transgenic goats secrete spider silk in their milk. The silk can be extracted and

spun into lightweight, strong fibres with many uses.

Another area of research involves developing transgenic animals that can serve as organ donors

for humans. Usually, the transplantation of organs from animals, such as pigs, into human

patients has very limited success because an antigen that is produced by the animal cells causes

a serious immune response. Some people are concerned about the risk of transferring diseases

from pigs to humans. Other people ask whether it is ethical to create new kinds of animals

purely for the purpose of harvesting their organs.

Assessing the Risks: When deciding whether or not to approve a transgenic product for use in

Canada, agencies consider a number of criteria, including:

• The potential social, economic, and environmental costs and benefits

• The process by which the product was made, including the source of the genetic material

• The biological characteristics of the transgenic product, compared with the characteristics of

the natural variety

• The potential health effects, including the possibility that the product may contain toxins or

allergens

Many organizations and citizen groups have opposed the use of transgenic organisms. Below

are some of the risks cited by these groups:

• Environmental threats: The use of herbicide-resistant plants could encourage farmers to use

higher levels of herbicides. This, in turn, could lead to a buildup of herbicide chemicals in water

supplies and neighbouring ecosystems. As well, there is evidence that engineered genes can be

transferred to wild plants and other organisms, raising concerns about the emergence of

“superweeds” and “superbugs.” More generally, ecosystems involve complex and delicate

balances among many different organisms. The introduction of transgenic bacteria, plants, or

animals could upset these balances, with unknown results.

• Health effects: Many consumer groups argue that not enough is known about the long-term

effects of consuming transgenic products, including genetically modified foods and medicines.

The complex processes of gene regulation are not well understood, so it is difficult to predict

potential health risks.

• Social and economic issues: Advocates of genetically modified foods argue that these foods

will help to improve human health and alleviate world hunger. Their opponents argue that

genetic research absorbs millions of dollars, which would be better spent directly helping

people in need. In addition, as mentioned earlier, many people are concerned about the

growing influence of private corporations over global food production.

The treatment of plants and animals as commodities to be manipulated and patented also

raises questions about our relationships with—and responsibilities to—other living organisms.

Patenting Organisms and Genes

Some people are concerned about the loss of traditional ways of life and the increasing

dependence of farmers on the corporations that patent seeds.

Others are concerned about world food production becoming concentrated in the hands of

private companies. These companies, however, play an important role in genetics research and

in the development of gene technologies and products that have important public benefits.

Gene patents offer a way to reward their investment and innovation.