Tools of Genetic Engineering

Genetic engineering (recombinant DNA technology) involves isolating a gene from one organism and inserting it into another. This requires molecular tools to cut, join, and transfer DNA.

The Genetic Engineering Process

1. Cut the Gene

Restriction enzymes cut DNA at specific recognition sequences, creating sticky or blunt ends

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2. Insert into Vector

The gene is inserted into a plasmid (vector) using DNA ligase to join the fragments

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3. Transform Host Cell

The recombinant plasmid is introduced into a host cell (e.g., bacterium)

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4. Select and Grow

Transformed cells are identified (e.g., antibiotic resistance) and cultured

Restriction Enzymes

Molecular scissors that cut DNA at specific base sequences. Each enzyme recognises a particular palindromic sequence. They produce sticky ends (overhangs) or blunt ends.

DNA Ligase

The molecular glue that joins DNA fragments together by forming phosphodiester bonds between the sugar-phosphate backbones.

Vectors and Transformation

A vector is a DNA molecule used to carry a foreign gene into a host cell. The most common vectors are bacterial plasmids -- small, circular DNA molecules that can replicate independently.

Key Vector Features

Origin of Replication

Allows the plasmid to be copied inside the host cell.

Selectable Marker

An antibiotic resistance gene to identify cells that have taken up the plasmid.

Multiple Cloning Site

A region with many restriction enzyme sites where foreign DNA can be inserted.

Promoter Region

Ensures the inserted gene is transcribed in the host cell.

Transformation: The process of introducing recombinant DNA into a host cell. Methods include heat shock (bacteria), electroporation (electrical pulses), or using a gene gun (plants).

Applications and Ethical Considerations

Genetic engineering has transformative applications in medicine, agriculture, and industry, but also raises important ethical questions.

Benefits

• Medicine: Insulin production, gene therapy for genetic disorders
• Agriculture: Drought-resistant and pest-resistant crops (GMOs)
• Industry: Enzymes for manufacturing, biofuels
• Research: Understanding gene function, disease models

Ethical Concerns

• Environmental: Gene transfer to wild populations, reduced biodiversity
• Health: Unknown long-term effects of consuming GMOs
• Social: Corporate ownership of genetic material, access inequality
• Moral: Is it ethical to modify living organisms? Designer babies?

In Australia: The Office of the Gene Technology Regulator (OGTR) oversees all work involving genetically modified organisms, ensuring safety for people and the environment.

Key Vocabulary

Restriction Enzyme

An enzyme that cuts DNA at specific recognition sequences, producing fragments with sticky or blunt ends.

Vector

A DNA molecule (usually a plasmid) used to carry a foreign gene into a host cell for replication and expression.

Transformation

The process of introducing recombinant DNA into a host cell so the foreign gene can be expressed.

GMO

A genetically modified organism whose DNA has been altered using genetic engineering techniques.

Worked Examples

1

Describe how human insulin is produced using genetic engineering.

Step 1: The human insulin gene is identified and cut from human DNA using a restriction enzyme (or synthesised).

Step 2: A bacterial plasmid is cut with the same restriction enzyme. The insulin gene is inserted using DNA ligase.

Step 3: The recombinant plasmid is introduced into E. coli bacteria via transformation.

Step 4: Transformed bacteria are grown in fermenters, where they express the insulin gene and produce human insulin, which is then purified.

2

Explain why the same restriction enzyme must be used to cut both the gene and the plasmid.

Step 1: Restriction enzymes produce complementary sticky ends when they cut DNA.

Step 2: Using the same enzyme ensures the gene fragment and the cut plasmid have matching sticky ends.

Step 3: Matching sticky ends allow base pairing between the fragments, enabling DNA ligase to join them together to form recombinant DNA.

3

Discuss one benefit and one ethical concern of genetically modified crops.

Benefit: GM crops can be engineered for pest resistance (e.g., Bt cotton), reducing the need for pesticides, lowering costs for farmers, and reducing environmental chemical use.

Ethical concern: Modified genes could transfer to wild plant populations through cross-pollination, potentially creating invasive species or reducing genetic diversity in natural ecosystems.

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

Restriction enzymes are used in genetic engineering to:

Join DNA fragments together Translate mRNA into protein Copy DNA during replication Cut DNA at specific recognition sequences

Question 2

A plasmid used in genetic engineering is an example of a:

Vector Ligase Restriction enzyme Chromosome

Question 3

Why is an antibiotic resistance gene included in a plasmid vector?

To make the bacteria grow faster To select cells that have taken up the plasmid To cut the foreign gene To prevent mutation

Question 4

The enzyme that joins DNA fragments together is:

DNA polymerase Helicase DNA ligase RNA polymerase

Question 5

Which of the following is a valid ethical concern about genetically modified crops?

They always taste worse than non-GM crops Genetic engineering is too expensive to use GM crops cannot grow in soil Modified genes could spread to wild populations via cross-pollination

Genetic Engineering