B6 - Genetic Engineering, GM and DNA Fingerprinting

Question 1

What are two well established examples of products made using genetic engineering?

Answer 1

• insulin: used by people with diabetes to control their blood sugar
• human growth hormone: used to treat people with reduced growth

Question 2

What is the process of genetic engineering ?

Answer 2

1. Identifying the gene that codes for the protein to be produced.
2. Removing it from the donor, e.g. a human cell.
3. Introducing it into a host, the bacterium.
4. Growing the bacteria on a large scale to make the product.

Question 3

Explain how insulin is made.

Answer 3

• the insulin gene is removed from human DNA. The gene is cut from the rest of the DNA by enzymes called restriction enzymes
• a loop of bacterial DNA called a plasmid is removed from the bacterial cell
• the plasmid is cut open using the same restriction enzyme
• the human insulin gene and plasmid are mixed, which results in the human gene inserted between the cut ends of the plasmid. The cut surfaces of the DNA are repaired using ligase.
• this is now inserted into a new bacterium. The plasmid is a vector as it carries the human gene
• the bacteria are now called transgenic bacteria, because they have DNA from another organism. They are grown in large numbers to produce the insulin for us.

Question 4

How are the bacteria cloned in genetic engineering?

Answer 4

The bacteria are placed in a large container called a fermenter. Here ideal conditions can be provided for their rapid growth and reproduction. The bacteria divide asexually, producing genetically identical copies of themselves. This is called cloning. The resulting large culture of bacteria will make large amounts of the insulin protein. This is harvested and packaged.

Question 5

What is assaying technique?

Answer 5

The assaying is done by growing the bacteria on agar with a coloured dye. The plasmid that carries the human gene also has a second gene included in it. This gene codes for an enzyme that causes a colour change in a dye, turning it blue. One of two possible events will happen on the agar:
• If the human insulin gene is in the plasmid, it damages the gene that makes the colour-change enzyme. So no colour-change enzyme is produced, and the agar around the bacteria will stay colourless.
• If the human insulin gene is not present, the colour- change gene will be intact, and will make the enzyme. The result will be that the agar will go blue.

The colourless colonies of bacteria are selected and cloned.

Question 6

Give some examples of characteristics transferred by GM technology.

Answer 6

• pesticide resistance in plants
• frost resistance in fruit
• increased shelf life in fruit
• increased milk yield in cattle.

Question 7

How is a GM organism created?

Answer 7

• the gene that controls a useful characteristic such as pesticide resistance is identified in a plant
• the gene is cut out of the pesticide - repellent plant using restriction enzymes
• the DNA of a carrier or vector for example a virus, is cut open using the same restriction enzymes
• the useful tense is spliced into the viral DNA. The combined DNA is placed in a viral vector. The DNA is injected into a plant cell ( insertion )
• the new gene is inserted into the host of DNA
• the new gene beings to work. The host is now a transgenic organism - a genetically modified organism.
• the gm organism is cloned producing large large numbers of identical individuals, all resistant to the pesticide.

Question 8

How do restriction enzymes work?

Answer 8

Restriction enzymes make very precise cuts through the DNA. Remember that DNA is made of two parallel strands, with bases between them. Restriction enzymes do not cut straight across the strands – most of them make a staggered cut, leaving a few unpaired bases exposed on the ends of the strands. The cut surfaces are called ‘sticky ends’.

Question 9

How does ligase work?

Answer 9

The new gene to be added is also cut by the same restriction enzyme, creating the same types of sticky ends. The new gene will therefore t into the vector’s cut DNA, and the sticky ends will come together. The enzyme DNA ligase repairs the paired DNA strands.

Question 10

How do forensic scientists prepare a DNA fingerprint?

Answer 10

1. A sample of human tissue is collected from the scene of a crime, such as blood, skin, hair, or semen.
2. The DNA is extracted from the cells.
3. The DNA is cut into fragments using restriction enzymes.
4. Since each person has different DNA, the restriction enzymes cut in different places, producing fragments of different lengths.
5. The fragments are separated using a kind of chromatography called electrophoresis. They are separated according to their size – smaller fragments travel further.
6. A series of colourless bands is produced on the gel.
7. To make the bands visible, a radioactive probe is added which sticks to the DNA. This can then be detected on film. The result is a film with a series of black and white bands. This is called an autoradiograph.
8. The forensic scientist compares the positions of the bands to identify the suspect.
9. The position of the bands should match if the suspect and the sample from the scene of the crime have the same DNA.

Question 11

What are the pros and cons of storing DNA data?

Answer 11

This is useful for the police, as they can build up a large database of DNA ngerprints. It makes it easy to compare forensic evidence with the records of many potential suspects.

However, many people argue that storing the DNA fingerprints of innocent people is an invasion of privacy. They feel that their records should not be kept if they have not done anything wrong.