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Genetic Engineering
Aspects of Genetic Engineering
| Question | Answer |
|---|---|
| Define genetic engineering (recombinant DNA technology) | The use of technology in the removal (or synthesis) and alteration of genes and the transfer of genes from one organism to another. |
| How is it possible for DNA to be transferred between different species? | DNA is universal. The nucleotides which make up DNA are the same in almost all organisms. All cells can 'read' the genetic code so the the protein that is encoded by the gene can be produced in any cell. |
| Define recombinant DNA (rDNA) | DNA which has been modified and contains genes from more than species or organisms. |
| Define genome. | The complete set of genetic material of an organism ( or a population of organisms). |
| T or F. Genetic engineering alters the genome of an organism. | T |
| What is the name of an organism which contains altered genes? | Recombinant organism/ transgenic organisms / genetically modified organism(GMO) |
| What is the role of restriction endonucleases (enzymes) in genetic engineering? | They cut DNA at specific sites that are called restriction sites to provide sticky or blunt ends which are available to be joined with other DNA. |
| Restriction sites on DNA are palindromic. What does this mean? | The site reads the same in the 5' to 3' direction as in the 3' to 5' direction. Examples of palindromic English words : level, madam, civic ... |
| What is a vector? | A carrier which is used to move a foreign gene into a host organism. Plasmids are the most common type of vector. Viruses and liposomes can also be used. |
| What is a plasmid? | A circular strand of DNA found in the cytoplasm of bacterial cells. It carries one or several genes and can replicate itself independently of the host. |
| State 3 major features of plasmids which make them a suitable vector. | 1) Small and easily taken up by bacterial host cells. 2) Replicate rapidly and independently of host cell. 3) Have many restriction sites so different restriction enzymes can be used. 4) Possess marker genes which make them easily identified. |
| T or F. The plasmid and the DNA from the organism must be cut with the same restriction enzyme so that complementary ends will be created. | T |
| What is the role of DNA ligase in genetic engineering? | After the gene has been combined with the plasmid and complementary base pairs have formed by hydrogen bonds; DNA ligase is added to form the covalent phosphodiester bonds of the sugar-phosphate backbone of the recombinant DNA. |
| List the basic steps involved in genetic engineering. | 1. Identify and isolate gene 2. Join gene with a vector (e.g. plasmid) 3. Introduce vector into a suitable host cell (e.g. bacteria) 4. Select transformed (recombinant) cells 5. Multiplication or expression of gene or gene product of interest. |
| What is transformation of bacteria? | This refers to bacterial host cells which have taken up recombinant DNA (rDNA). They are called transformed because they now have foreign DNA. |
| How are bacteria prepared for transformation? | They are treated with calcium ions, cooled and then given a heat shock to increase chances of plasmids passing through the cell surface membrane. |
| Some plasmids do not take up the foreign gene and some bacteria do not take up plasmids. How can the transformed bacteria be identified? | 1) In plasmids containing antibiotic resistance genes, the bacteria which contain them will also be antibiotic resistant. 2) In plasmids containing fluorescence genes from jelly-fish; under UV-light the bacteria will fluoresce. |
| What is the difference between the terms transgenic and transformed in bacteria? | Upon taking in the plasmid, the bacterial host cells is transformed. After DNA polymerase in bacteria copies the plasmids; the cell divides and the foreign gene is transcribed and translated, the bacteria is called transgenic. |
| What is the role of the hormone insulin in the body? | To decrease the concentration of glucose in the blood when it raises above the normal value. |
| What is diabetes mellitus? | A disorder caused by an inability to produce insulin or the inability of cells to respond to insulin. |
| What is type 1 diabetes? | Insulin dependent diabetes. Caused by an inability to secrete insulin possible due to the destruction of the Beta cells of the islets of Langerhans in the pancreas from a young age. |
| What is type 2 diabetes? | Non-insulin dependent diabetes. An inability of cells to respond to insulin possibly due to fewer receptors on the cell surface membranes of target cells. Often associated with obesity, high sugar diet and ethnicity. |
| How can type 1 and 2 diabetes be controlled? | Type 1 - injections of insulin Type 2 - diet and exercise; insulin injections may be required at later stages. |
| Outline steps 1-3 in insulin production (gene isolation) | 1. Insulin-producing beta-cells obtained from human pancreas. 2. mRNA extracted from beta-cells. 3. Extracted mRNA incubated with enzyme reverse transcriptase to make complementary single stranded cDNA. |
| Outline steps 4 -5 in insulin production (gene isolation) | 3. Extracted mRNA incubated with enzyme reverse transcriptase to make complementary single stranded cDNA. 4. cDNA incubated with DNA polymerase and free nucleotides to form double stranded DNA copy of gene. 5. Many copies of gene made by using PCR |
| Outline steps 6-7 in insulin production (gene insertion into vector) | 6. A plasmid (small circular DNA) is used as a vector (go-between) to transfer genetic material into the recipient bacteria. 7. Bacterial cell walls dissolved with enzymes to extract plasmids. |
| Outline steps 8-10 in insulin production (gene insertion into vector) | 8. Treat DNA to be inserted with the same restriction enzyme to cut the DNA at identical points. 9. Mix treated DNA and treated plasmids. 10. Use enzyme DNA ligase to link together DNA units to form recombinant plasmid (vector) |
| What happens after recombinant plasmid containing insulin DNA is obtained? | A host bacteria is treated with calcium ions, cooled then heat shocked to take up the plasmid. The bacterium then divides rapidly producing proinsulin. This has to be cleaved with enzymes to produce human insulin. |
| Insulin was initially made by genetically engineering bacteria to produce it. However, in more recent times, eukaryotic cells such as yeast are used instead of bacteria to produce insulin. Why ? | Insulin has 2 polypeptide chains and bacteria do not modify proteins in the right way to form a functioning insulin molecule. Eukaryotic cells are able to do this better than bacteria. |
| What is gene therapy? | The treatment of a disease by manipulating the genes in a person's cells. |
| Describe the cause and effect of cystic fibrosis. | It is a genetic disorder caused by a faulty CFTR protein on which does not properly transport Cl- ions out of the alveoli. This results in build-up of thick, sticky mucus. Patients are prone to bacterial infection and have to take various medicines. |
| What is the aim of gene therapy in CF patients? | To introduce the correct version of the CFTR gene. However these have all had major challenges as the cells of the respiratory tract are short lived and need to be replaced frequently. |
| Describe the cause and effect of severe combined immunodeficiency syndrome (SCID) | A faulty allele in the gene coding for the enzyme adenosine deaminase (ADA) which is essential for the proper working of the immune system. SCID patients have very weak immune systems. |
| Describe the gene therapy process which was trialled to treat SCID. | Some T cells (white blood cells) from the patient were removed and the correct allele was inserted into the cells using a retrovirus vector. |
| What was the effect of the gene therapy trial run on SCID patients in the past? | At first it appeared successful however, several patients later developed Leukaemia due to the allele finding its way into an incorrect position where it affects the normal genes that control the cell cycle. |
| Distinguish between somatic gene therapy and germ line gene therapy. | Somatic gene therapy - involves modifying non-reproductive body cells . All examples in your texts fall under this category. Germ line gene therapy - would involve changing genes in reproductive cells (gametes). This is not legal in any country. |
| What is electrophoresis? | A DNA technology which involves separating different fragments of DNA according to their sizes. It can be used for DNA profiling in criminal investigations as well as confirm family relationships (paternity etc). |
| What is polymerase chain reaction (PCR)? | It is a gene technology which is used to rapidly used to produce a very large number of copies of a particular length of DNA. |
| What is CRISPRCas9 ? | A modern gene editing tool which can edit the existing genome of an organism by either modifying, deleting or inserting new sequences into the DNA more accurately and faster than prior technologies. |
| Give two advantages of using GM insulin over insulin taken directly from an animal? | 1) The amino acid sequence can be changed to alter the properties of the insulin to be more beneficial to humans. 2) Increasing supply for increasing demand. GM insulin is not affected by availability of animals/meat trade. |
| Give one disadvantage of using GM insulin. | Some persons have not experienced warning signs of a hypoglycaemic attack when blood glucose concentration falls increasing the likelihood of diabetic coma. |
| Give one issue with the use of antibiotic resistance genes in GMO's. | These genes could escape and be transferred to pathogenic organisms making some antibiotics redundant. |
| Give one issue with the use of herbicide resistance genes in certain GMO's. | These genes could be transferred in pollen to weed species and lead to the development of superweeds that are resistant to herbicides. |
| Give one disadvantage of GMO crops to small-scale farmers. | There is no advantage in terms of cost or reduction in chemicals used in agriculture. Farmers also cannot keep seed for sowing the following crop as GM crops do not 'breed true'. |
| T or F. Foreign genes could be transferred to non-GM crop plants and change their genomes; this may pollute those species that may prove useful sources of genes for crop improvement in the future. | T |
| List 3 examples of medicines produced by genetic engineering technology in medicine. | Insulin, human growth hormone, factor VIII, certain vaccines, thyroid stimulating hormone, monoclonal antibodies..etc |
| State 5 features which genetic engineering technology can be used to improve in plants. | 1) Disease resistance e.g. papaya 2) Pest resistance e.g. cotton 3) Herbicide resistance e.g. corn/soya/cotton 4) Drought resistance e.g. sugar cane/corn 5) Improved nutritional qualities e.g. rice/Irish potato |
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CAPE Biology Unit 1
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