Genetic engineering process

What is Genetic Engineering?

Have you ever wondered how bacteria can be programmed to produce human medicines like insulin? This is achieved through genetic engineering.
Genetic engineering involves taking a desired gene from one organism's donor DNA and inserting it into the genome of another organism.
The organism that receives the new genetic material is called the host cell, and once modified, it becomes a transgenic organism.
When DNA from two different species is successfully joined together, the resulting molecule is known as recombinant DNA.

The Molecular Tools

To move DNA between organisms, scientists rely on specific biological tools to cut, carry, and paste the genetic material.

Restriction enzymes act as chemical scissors. They recognise specific short sequences of bases and cut the DNA at these points.
When restriction enzymes cut the DNA, they often make a staggered cut. This leaves short, single-stranded overhangs of unpaired bases known as sticky ends.
A vector is a vehicle used to transport the foreign DNA into the host cell. Common vectors include viruses or plasmids (small, circular loops of DNA found in bacteria, separate from their main chromosome).
DNA ligase acts as the chemical glue. It joins the two matching fragments of DNA together by forming covalent bonds in the sugar-phosphate backbone.

The Step-by-Step Process

Genetic engineering must be carried out in a strict sequence to ensure the recombinant DNA is formed and expressed correctly.

Isolation: The desired gene is identified and cut out of the donor DNA using a restriction enzyme.
Preparation: A vector (such as a bacterial plasmid) is cut open using the exact same restriction enzyme. This is crucial because it ensures both the gene and the vector have complementary sticky ends.
Ligation: The isolated gene and the open vector are mixed together. Their complementary sticky ends pair up, and DNA ligase is added to join their sugar-phosphate backbones, creating recombinant DNA.
Transformation: The recombinant vector is inserted into the host cell (e.g., a bacterium).
Selection: Scientists identify which cells successfully took up the recombinant vector using markers.
Expression: The successfully modified bacteria are grown in a large fermenter, reproducing rapidly (up to every 20 minutes) to mass-produce the desired protein.

Selecting the Successful Cells

The transformation process is highly inefficient, meaning only a very small percentage of host bacteria will actually take up the recombinant plasmid.
To solve this, scientists use an antibiotic resistance marker (a type of marker gene). This gene is physically linked to the desired target gene on the same plasmid.
The mixture of bacteria is spread onto an agar plate containing a specific antibiotic.
Non-transformed bacteria (which did not take up the plasmid) are killed by the antibiotic. Only the successfully transformed bacteria possess the resistance gene, allowing them to survive, grow into colonies, and be identified.

Worked Example

A scientist mixes 2,500 E. coli bacteria with recombinant plasmids containing a gene for human growth hormone and a marker gene for ampicillin resistance. They spread the mixture onto an agar plate containing ampicillin. After 24 hours, they observe 40 distinct bacterial colonies. Explain what has happened to the bacteria.

Step 1: Identify the fate of the non-transformed bacteria.

$2,500 - 40 = 2,460$ bacteria did not take up the recombinant plasmid. Because they lack the ampicillin resistance marker, they were killed by the antibiotic.

Step 2: Identify the fate of the transformed bacteria.

The 40 surviving colonies possess the ampicillin resistance marker, meaning they successfully took up the recombinant plasmid.

Step 3: State the final conclusion regarding the target gene.

Because the marker gene is on the same plasmid as the human growth hormone gene, the scientist can confidently identify that these 40 colonies contain the target genetic material.

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Exam Tips

Common Mistake
Students often confuse the 'vector' with the 'host'. Remember: the vector is the taxi (e.g., the plasmid) that carries the gene, and the host is the destination (e.g., the bacterium).
Common Mistake
Do not state that the goal of using antibiotic markers is to 'create superbugs'; it is merely a laboratory tool to identify which bacteria took up the plasmid.
3
For Higher Tier questions on ligase, always specify that it joins the 'sugar-phosphate backbone' to guarantee the mark.
4
When asked why antibiotic markers are used, examiners look for the exact phrase: 'To identify which cells have taken up the genetic material/plasmid'.
5
If a question asks about genetically modifying a multicellular organism (like a plant or animal), state that the gene must be inserted at an early stage of development (e.g., into the embryo) so that mitosis ensures every adult cell contains the new gene.

Key Terms(12)

Donor DNA: The original genetic material from which a desired gene is extracted for genetic engineering.
Host cell: The recipient organism (such as a bacterium, plant, or animal) into which foreign genetic material is transferred.
Transgenic organism: An organism that contains DNA from a different species as a result of genetic engineering.
Recombinant DNA: A single DNA molecule formed by joining genetic material from two different organisms.
Restriction enzyme: An enzyme that recognises specific sequences of DNA and cuts the sugar-phosphate backbone, often creating sticky ends.
Sticky ends: Short, single-stranded overhangs of unpaired bases at the ends of a DNA fragment, created by a staggered cut from a restriction enzyme.
Vector: A DNA molecule (like a plasmid or virus) used as a vehicle to artificially carry foreign genetic material into another cell.
Plasmid: A small, circular loop of DNA found in the cytoplasm of bacteria that can replicate independently of the main bacterial chromosome.
DNA ligase: An enzyme used to join two fragments of DNA together by forming chemical bonds in their sugar-phosphate backbones.
Transformation: The process by which a host cell takes up a recombinant vector from its surrounding environment.
Antibiotic resistance marker: A gene inserted into a vector that allows scientists to identify successfully transformed cells by enabling them to survive in the presence of an antibiotic.
Marker gene: A gene used to indicate that the target gene has been successfully incorporated into the host organism.

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Key Terms(12)

Donor DNA: The original genetic material from which a desired gene is extracted for genetic engineering.
Host cell: The recipient organism (such as a bacterium, plant, or animal) into which foreign genetic material is transferred.
Transgenic organism: An organism that contains DNA from a different species as a result of genetic engineering.
Recombinant DNA: A single DNA molecule formed by joining genetic material from two different organisms.
Restriction enzyme: An enzyme that recognises specific sequences of DNA and cuts the sugar-phosphate backbone, often creating sticky ends.
Sticky ends: Short, single-stranded overhangs of unpaired bases at the ends of a DNA fragment, created by a staggered cut from a restriction enzyme.
Vector: A DNA molecule (like a plasmid or virus) used as a vehicle to artificially carry foreign genetic material into another cell.
Plasmid: A small, circular loop of DNA found in the cytoplasm of bacteria that can replicate independently of the main bacterial chromosome.
DNA ligase: An enzyme used to join two fragments of DNA together by forming chemical bonds in their sugar-phosphate backbones.
Transformation: The process by which a host cell takes up a recombinant vector from its surrounding environment.
Antibiotic resistance marker: A gene inserted into a vector that allows scientists to identify successfully transformed cells by enabling them to survive in the presence of an antibiotic.
Marker gene: A gene used to indicate that the target gene has been successfully incorporated into the host organism.

Genetic engineering process

What is Genetic Engineering?

Have you ever wondered how bacteria can be programmed to produce human medicines like insulin? This is achieved through genetic engineering.
Genetic engineering involves taking a desired gene from one organism's donor DNA and inserting it into the genome of another organism.
The organism that receives the new genetic material is called the host cell, and once modified, it becomes a transgenic organism.
When DNA from two different species is successfully joined together, the resulting molecule is known as recombinant DNA.

The Molecular Tools

To move DNA between organisms, scientists rely on specific biological tools to cut, carry, and paste the genetic material.

Restriction enzymes act as chemical scissors. They recognise specific short sequences of bases and cut the DNA at these points.
When restriction enzymes cut the DNA, they often make a staggered cut. This leaves short, single-stranded overhangs of unpaired bases known as sticky ends.
A vector is a vehicle used to transport the foreign DNA into the host cell. Common vectors include viruses or plasmids (small, circular loops of DNA found in bacteria, separate from their main chromosome).
DNA ligase acts as the chemical glue. It joins the two matching fragments of DNA together by forming covalent bonds in the sugar-phosphate backbone.

The Step-by-Step Process

Genetic engineering must be carried out in a strict sequence to ensure the recombinant DNA is formed and expressed correctly.

Isolation: The desired gene is identified and cut out of the donor DNA using a restriction enzyme.
Preparation: A vector (such as a bacterial plasmid) is cut open using the exact same restriction enzyme. This is crucial because it ensures both the gene and the vector have complementary sticky ends.
Ligation: The isolated gene and the open vector are mixed together. Their complementary sticky ends pair up, and DNA ligase is added to join their sugar-phosphate backbones, creating recombinant DNA.
Transformation: The recombinant vector is inserted into the host cell (e.g., a bacterium).
Selection: Scientists identify which cells successfully took up the recombinant vector using markers.
Expression: The successfully modified bacteria are grown in a large fermenter, reproducing rapidly (up to every 20 minutes) to mass-produce the desired protein.

Selecting the Successful Cells

The transformation process is highly inefficient, meaning only a very small percentage of host bacteria will actually take up the recombinant plasmid.
To solve this, scientists use an antibiotic resistance marker (a type of marker gene). This gene is physically linked to the desired target gene on the same plasmid.
The mixture of bacteria is spread onto an agar plate containing a specific antibiotic.
Non-transformed bacteria (which did not take up the plasmid) are killed by the antibiotic. Only the successfully transformed bacteria possess the resistance gene, allowing them to survive, grow into colonies, and be identified.

Worked Example

Step 1: Identify the fate of the non-transformed bacteria.

$2,500 - 40 = 2,460$ bacteria did not take up the recombinant plasmid. Because they lack the ampicillin resistance marker, they were killed by the antibiotic.

Step 2: Identify the fate of the transformed bacteria.

The 40 surviving colonies possess the ampicillin resistance marker, meaning they successfully took up the recombinant plasmid.

Step 3: State the final conclusion regarding the target gene.

Because the marker gene is on the same plasmid as the human growth hormone gene, the scientist can confidently identify that these 40 colonies contain the target genetic material.

Sign up to continue reading

Get full access to revision notes, key terms, and exam tips for every subtopic.

Exam Tips

Common Mistake
Students often confuse the 'vector' with the 'host'. Remember: the vector is the taxi (e.g., the plasmid) that carries the gene, and the host is the destination (e.g., the bacterium).
Common Mistake
Do not state that the goal of using antibiotic markers is to 'create superbugs'; it is merely a laboratory tool to identify which bacteria took up the plasmid.
3
For Higher Tier questions on ligase, always specify that it joins the 'sugar-phosphate backbone' to guarantee the mark.
4
When asked why antibiotic markers are used, examiners look for the exact phrase: 'To identify which cells have taken up the genetic material/plasmid'.
5
If a question asks about genetically modifying a multicellular organism (like a plant or animal), state that the gene must be inserted at an early stage of development (e.g., into the embryo) so that mitosis ensures every adult cell contains the new gene.

Key Terms(12)

Donor DNA: The original genetic material from which a desired gene is extracted for genetic engineering.
Host cell: The recipient organism (such as a bacterium, plant, or animal) into which foreign genetic material is transferred.
Transgenic organism: An organism that contains DNA from a different species as a result of genetic engineering.
Recombinant DNA: A single DNA molecule formed by joining genetic material from two different organisms.
Restriction enzyme: An enzyme that recognises specific sequences of DNA and cuts the sugar-phosphate backbone, often creating sticky ends.
Sticky ends: Short, single-stranded overhangs of unpaired bases at the ends of a DNA fragment, created by a staggered cut from a restriction enzyme.
Vector: A DNA molecule (like a plasmid or virus) used as a vehicle to artificially carry foreign genetic material into another cell.
Plasmid: A small, circular loop of DNA found in the cytoplasm of bacteria that can replicate independently of the main bacterial chromosome.
DNA ligase: An enzyme used to join two fragments of DNA together by forming chemical bonds in their sugar-phosphate backbones.
Transformation: The process by which a host cell takes up a recombinant vector from its surrounding environment.
Antibiotic resistance marker: A gene inserted into a vector that allows scientists to identify successfully transformed cells by enabling them to survive in the presence of an antibiotic.
Marker gene: A gene used to indicate that the target gene has been successfully incorporated into the host organism.

Previous Subtopic: Genetic engineering definitionGenetic engineering definition Next Subtopic: Gene technology benefits and risksGene technology benefits and risks

Back to Genetic engineering process

Put your knowledge into practice — try past paper questions for Biology A

Key Terms(12)

Donor DNA: The original genetic material from which a desired gene is extracted for genetic engineering.
Host cell: The recipient organism (such as a bacterium, plant, or animal) into which foreign genetic material is transferred.
Transgenic organism: An organism that contains DNA from a different species as a result of genetic engineering.
Recombinant DNA: A single DNA molecule formed by joining genetic material from two different organisms.
Restriction enzyme: An enzyme that recognises specific sequences of DNA and cuts the sugar-phosphate backbone, often creating sticky ends.
Sticky ends: Short, single-stranded overhangs of unpaired bases at the ends of a DNA fragment, created by a staggered cut from a restriction enzyme.
Vector: A DNA molecule (like a plasmid or virus) used as a vehicle to artificially carry foreign genetic material into another cell.
Plasmid: A small, circular loop of DNA found in the cytoplasm of bacteria that can replicate independently of the main bacterial chromosome.
DNA ligase: An enzyme used to join two fragments of DNA together by forming chemical bonds in their sugar-phosphate backbones.
Transformation: The process by which a host cell takes up a recombinant vector from its surrounding environment.
Antibiotic resistance marker: A gene inserted into a vector that allows scientists to identify successfully transformed cells by enabling them to survive in the presence of an antibiotic.
Marker gene: A gene used to indicate that the target gene has been successfully incorporated into the host organism.