IMPORTANT!  The following is one of the write-up questions in the final exam.  Do not hand in the answers before the exam.  You will need to write the answers in the exam question book. 

Choose one of the following terms: genetic testing, therapeutic cloning, reproductive cloning, gene therapy.  Answer the questions using no more than three sentences.

         1. Explain the term/technology (1 point).                       

         2. Describe its potential benefit(s) to our lives (2 points).

 

Chapter 12 DNA technology and the human genome

 

1. Recombinant DNA technology                            

- Combines different pieces of DNA (recombinant DNA) to manufacture genes and gene products.

 

A. Gene cloning

Gene cloning is the process of producing multiple copies of a gene, using recombinant DNA.

 

Recombinant DNA is generated by the process of ‘cut and paste’, in which restriction enzymes work as scissors and DNA ligase as glue.  (Fig 12.4, p235)

 

Restriction enzymes are bacterial enzymes that cut DNA at specific sites. 

- Recognize a short nucleotide sequence. 

Example: The restriction enzyme in Fig 12.4 recognizes the DNA sequence GAATTC.

- Hundreds of restriction enzymes have been isolated.

- There are over a hundred different recognition sequences. 

- Some restriction enzymes produce ‘sticky ends’ to the target DNA molecules after digestion.

 

DNA ligase joins DNA fragments together.  ‘Sticky ends’ assist the joining of DNA fragments.

 

Plasmids are small circular DNA molecules in bacteria cells.

- In nature, a plasmid serves as a vector, which transfers genetic information from one bacterium to another.

- Plasmids are used as tools to manufacture multiple copies of recombinant DNA in bacteria (typically E. coli cells).

 

                                                 Creation of recombinant DNA                                Process of gene cloning (Fig 12.5, p236)

                

 

B. Polymerase Chain Reaction (PCR) (Fig 12.12, p242)

- Amplification of DNA molecule in test tubes.

- Amplifies trace amount of DNA molecule.

- The DNA fragments are duplicated during each cycle of PCR reaction. (Each cycle typically lasts for a few minutes.)

- The amount of DNA after n cycles of PCR reaction should be 2ⁿ.

Examples: After 10 cycles of PCR reaction, single DNA molecule should amplify to about a thousand molecules (2¹⁰=1024).

                After 20 cycles of PCR reaction, single DNA molecule should amplify to about a million molecules (2²⁰).

Different applications of PCR include:

- Gene cloning.

- Gene cloning from fossils.

- DNA detection in crime scenes.

- Virus detection.

 

C. Application of recombinant DNA technology (Genetic engineering)

 

i) Production of protein products

- Manufacture of proteins for medical and/or industrial purposes.

- Proteins may be produced in a variety of organisms, such as E. coli, yeast, animal or plant cells.

- Each organism has advantages and disadvantages.

            Examples: insulin production in E. coli, production of vaccines in yeast

 

ii) Genetically modified (GM) organisms in agriculture

- Organisms may be genetically modified for the purpose of enhancing the organism’s value.

- Genetic engineering is a more direct way of improving crop traits than traditional breeding.

- Genetically modified organisms are also called transgenic organisms.

            Examples of GM organisms:      

Transgenic potatoes carrying toxin (Bt toxin) to insects ® minimize use of insecticides

‘Golden rice’ ® Vitamin A enriched rice

Transgenic plants/animals with enhanced growth.

- GM plants are becoming common, whereas commercialization of GM animals has been much slower.

 

Safety Concerns

- Recombinant microbes may escape to the nature to create new pathogens.

            ® Scientists must follow a strict guideline to prevent the microbes from leaving the laboratory.

- Effects of GM plants and animals on human health?

            ® Rigorous safety testing before commercialization.

- GM plants may cross with wild relatives.  If the herbicide resistance gene escapes to wild plant population, this may create ‘superweeds’.

            ® Guideline to prevent ‘escapes’. 

            ® ‘Escape’ can be prevented by making GM plants sterile

- Insect resistant GM plants may have unintended effects on other insects.

            ® This has not been confirmed in the field.

 

iii) Gene therapy

- Introduction of recombinant DNA to human cells/tissues.

- Gene therapy has potential for treating a variety of disease.

            cancer, arthritis, heart disease, etc.

- However, attempts to correct genetic defects via gene therapy have not been successful because of short lived activity of introduced genes.                     

Example of gene therapy strategy (Fig 12.9, p249):

Social and ethical questions

- Who should have access to the procedures?

- Should gene therapy be reserved for serious disease?

- Should we allow gene therapy for altering other traits?