Genetic Technologies Genetic engineering Gene therapy Genetic Engineering

Genetic Technologies Genetic engineering Gene therapy

Genetic Engineering Use the website to research the answers to the questions on your sheet. Be ready to discuss the answers next lesson.

Using technology to modify organisms Crop plants and domestic animals have been modified over generations using selective breeding, to produce organisms with desirable characteristics. Recombinant DNA technology can now be used to alter the genetic makeup of organisms much more quickly. Some genetically modified organisms are already being produced. In 2006, 252 million acres of transgenic crops were grown globally. 3 of 42 © Boardworks Ltd 2009

Types of GM crops Several different type of genetically-modified crops are currently being grown throughout the world. These include: l herbicide-resistant crops l pest-resistant crops – these include insect-resistant crops that have been engineered to produce a bacterial toxin that kills a specific pest. l disease-resistant crops l crops with increased nutritional value – these include Golden Rice. 4 of 42 © Boardworks Ltd 2009

Golden Rice that has been engineered to contain beta-carotene is known as Golden Rice. TM. Beta carotene is converted into vitamin A when digested. Golden Rice is thought to have potential benefits, as vitamin A deficiency currently affects a large number of people in economically less developed countries. 5 of 42 © Boardworks Ltd 2009

The production of Golden Rice plants naturally contain the gene for beta-carotene. This gene is expressed in the photosynthesizing parts of the plants. However, it is not expressed in the endosperm (grain). The production of beta-carotene relies on the presence of several enzymes. Not all of the enzymes are naturally available in the endosperm. In order to complete the biosynthetic pathway to restore the production of beta-carotene, scientists inserted two genes from other organisms into the rice genome, to complete the biosynthetic pathway. 6 of 42 © Boardworks Ltd 2009

Using genetically modified bacteria 7 of 42 © Boardworks Ltd 2009

Production of drugs Transgenic animals and plants can be modified to produce useful pharmaceuticals. This is known as pharming. For example, alpha-1 antitrypsin protects the lungs from damage during infection. Transgenic sheep can be produced that contain the gene for this protein. The gene can be pre-programmed to be expressed only in the mammary gland cells and secreted in milk. It can be extracted, purified and used for treating emphysema sufferers. 8 of 42 © Boardworks Ltd 2009

Xenotransplantation is the transfer of organs or tissues into humans from other species, including pigs. Transplanted organs are often rejected by the new host’s immune system, as antigens on the cells’ surface will be recognized as foreign. Recombinant DNA technology has been used to engineer pigs that lack an enzyme that is thought to contribute to transplant rejection. It is thought that with future developments xenotransplantation may be able to provide a large number of organ transplants. 9 of 42 © Boardworks Ltd 2009

The GM debate 10 of 42 © Boardworks Ltd 2009

Opinions on GM organisms

Gene therapy

Objectives How can gene therapy be used in the treatment of disease? What are the differences between somatic and germ line therapies? What are the advantages and disadvantages of gene therapy?

What is gene therapy? • Treatment of a genetic disease by providing the sufferer with a corrected copy of their defective gene. • Transfection is the technical term for inserting a corrected gene in to a cell.

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“Genetic disorders should not be corrected using gene therapy. Some people are born weaker than others and consequently die. . it’s called survival of the fittest. ” What do you think?

Cystic fibrosis is a heritable genetic disease that affects the secretory glands. Its main effect is to increase mucus production in the lungs. This mucus builds up, causing inflammation, narrowing the airways and leading to shortness of breath and an increased risk of infection. The symptoms of cystic fibrosis could potentially be reduced by replacing the defective gene that causes it with a healthy version, in the cells of the lungs where it is expressed. This approach to treatment is called gene therapy. 17 of 31 © Boardworks Ltd 2009

Gene therapy is a potential treatment for genetic diseases, involving altering the genotype. The cause of the disease is targeted, rather than just the symptoms. There are two ways of altering the genotype: 1. Replacing the defective gene with a normal allele 2. Supplementing the gene by adding copies of the normal allele, which must be dominant, to mask the effects of the defective (recessive) allele. 18 of 31 d D © Boardworks Ltd 2009

Gene therapy – types 19 of 31 © Boardworks Ltd 2009

There are two approaches to gene therapy: 1. Somatic cell therapy • Copies of the corrected gene are inserted directly into the somatic (body) cells of the sufferer. • Doesn’t prevent the disease from occurring in the next generation because it doesn’t affect the gametes. • Effects only last for the lifetime of the cells, so treatment has to be repeated.

*There are two approaches to gene therapy: 2. Germ line therapy • The corrected gene is inserted into a fertilised egg produced via IVF. • If successful, all cells of the embryo will contain the corrected gene. • Germ cell therapy is permanent and also ensures offspring inherit corrected gene. • Currently illegal.

Gene therapy and cystic fibrosis

Gene therapy and cystic fibrosis

Cystic fibrosis • Caused by mutant recessive allele. • Caused by a deletion mutation of 3 bases (AAA) in CFTR gene which encodes the CFTR protein. • Role of CFTR is to transport Cl- ions across epithelial cell membranes. Water follows by osmosis so membranes are kept moist and mucus runny. • In sufferers of cystic fibrosis, CFTR is non-functional so water is retained, membranes are dry and mucus is very sticky.

Sticky mucus causes the symptoms of cystic fibrosis • Thick, sticky mucus accumulates in lungs causing breathing difficulties and infections. Only treatment is antibiotics and physiotherapy. • Mucus blocks pancreatic duct so release of digestive enzymes affected (patients given enzymes instead) • Sperm duct blockage in males – infertility.

Physiotherapy

Gene therapy is targeted at the lungs • A vector is needed to introduce the corrected gene into cells of the lung. • Two main vectors you need to know about: 1. Harmless virus (retrovirus or adenovirus) 2. Liposomes

Carrying out gene therapy 29 of 31 © Boardworks Ltd 2009

Gene therapy - problems Lots of potential but not many successful trials because: • Liposomes sometimes not small enough to pass into the lung cells though the bronchioles. • Poor expression of the CFTR genes. • Adenoviruses may cause infection. • Adenoviruses may trigger immune response or patients may develop an immunity to them (useless for future treatments). • Patients have to undergo multiple rounds of gene therapy as effects short lived, depending on cell lifespan.

Ethical considerations - Gene Therapy • Are disabilities diseases? Should they be cured or prevented? • Does searching for the cure demean the lives of those who are presently affected by disabilities? • It is very expensive – so who’ll have access to these? And who’ll pay?