Topic 3.5 & Some Topic 7: Biotechnology and Genetic Modification/Nucleic Acids Flashcards

Question

# D.Biotechnology 1.Outline how gel electrophoresis separates proteins or fragments of DNA according to size.

Answer 1

Through gel electrophoresis, fragments of DNA are moved through an electric field and separated based on their size. 1.DNA samples are taken and amplified with PCR. 2.Restriction enzymes cut DNA into fragments at specific base sequences in each sample. 3.A fluorescent marker is bound to the DNA fragments or a dye is used, so that results can be seen. 4.Samples are added to a gel electrophoresis chamber. Electric current is passed through, pushing the fragments along. 5.Heavier fragments stay closer to the origin and smaller fragments go further. Negative fragments are moved to the right. 6.A banding pattern shows up for each DNA sample and can be compared.

Answer 2

* The polymerase chain reaction is a direct method of making multiple copies of a desired DNA sequence. * It is useful when only a small amount of DNA is available for testing as most DNA analysis tactics are impossible unless you have an ample amount of DNA. e.g. crime scene samples of blood, semen, tissue, hair, etc. * PCR occurs in a thermal cycler and involves a repeat procedure of 3 steps: 1.Denaturation: DNA sample is heated to separate it into two strands (94-96ºC) 2.Annealing: DNA primers attach to opposite ends of the target sequence (50-65ºC) 3. Extension: A heat-tolerant DNA polymerase (Taq) copies the strands (72ºC) * One cycle of PCR yields two identical copies of the DNA sequence

Answer 3

* DNA is often left behind at crime scenes and can provide loads of evidence e.g. crime scene samples of blood, semen, tissue, hair, etc. * 1986 DNA analysis was first called DNA fingerprinting and is now called DNA profiling or DNA testing for a clear distinction between traditional skin fingerprinting * it is easier to exclude a suspect than to convict someone based on a DNA match. The FBI estimates that one-third of initial rape suspects are excluded because DNA samples fail to match. * Precautions are taken to limit human mistakes however it is inevitable * DNA profiling can be used to determine: Inheritance of property, savings etc. Paternity investigation (samples are needed from the mother and father in question): Father is required to pay maintenance to support his biological child

Answer 4

Gene transfer: the introduction of new DNA into an existing organisms cell usually by vectors such as plasmids or modified viruses. Genetic modification using gene transfer: 1. The DNA plasmids in E. coli bacteria can be removed and used as a vector; what is used to transfer the gene from one species to another. 2. Restriction enzymes (endonucleases) ‘cut’ the desired gene from the genome. Or an easier way to obtain messenger RNA transcript is to use reverse transcriptase enzymes which can be used to make DNA copies of the RNA molecules called cDNA (complementary DNA). These copies can then be inserted into the plasmids for genetic modification. 3. The same restriction enzyme cuts into the plasmid 4. Because it is the same restriction enzyme the same bases are left exposed, creating ‘sticky ends’ 5. Ligase joins the sticky ends, fixing the gene into the E. coli plasmid 6. This recombinant plasmid is inserted into the host cell. It now expresses the new gene. An example of this is human insulin production. Other examples: golden rice with beta carotene to help with vitamin A production. Salt tolerant tomatoes to improve the yield and uniformity of crops in naturally salt affected areas.

Answer 5

Bt corn: Genes from Bt have been inserted into maize so GM plants can produce an insecticidal toxin and therefore be resistant to pests, e.g. European Corn Borer. Benefits: * **Greater resistance to pests**– Bt gene increases resistance to pests such as the European Corn Borer Bt was successfully introduced and Bt Corn is significantly more resistant to pests * **Increased productivity**– less land used / greater yield / less crop damage Maximum productivity has not increased, but losses in ‘bad’ years have been reduced. * **Less use of chemical pesticides** – reduced cost / reduced ecological damage Bt toxins are much more safer for humans and non-target organisms than most conventional insecticides Possible risks: * Could be **toxic to or cause allergic reactions in humans** Bt toxin has been used for 30 years without toxicity in humans being detected, however some experimental transgenic plants have caused allergic responses. * Transferred **genes could mutate** after testing * **Non-target organisms affected by toxins** & **Increases resistance** to toxin evolves in pests Bt is a very common soil bacterium – therefore organisms have regularly been exposed to Bt toxins previously. Negative effects on many non-target organisms thought to be minor … … However many species of caterpillars occur in and around cornfields during the growing season, and might be affected by Bt corn. Found risks: * **Accidental release may result in competition with native plant species** Unknown but there is a risk * Super weeds - **through cross-breeding the introduced gene could be transferred to wild varieties** known and there is evidence of superweeds evolved from other transgenic crops * **Biodiversity reduced** – both plant populations by direct **competition** and animal populations directly and indirectly could be affected Unknown ecosystem-wide risks, specific examples have been examined

Answer 6

* Caterpillar stage of the monarch butterfly exclusively feeds on milkweed, which grows on the edge of corn fields * Studies have shown that some mortality in monarch caterpillars fed on the milkweed leaves covered with Bt corn pollen First study, Laboratory condition: * To test this in 1999 A study was conducted where Monarch caterpillars were fed milkweed leaves that had been dusted with pollen from Bt corn * Growth and mortality rates were compared against caterpillars fed on non-dusted leaves or leaves dusted with non-GM pollen * Caterpillars exposed to Bt pollen were found to have eaten less, grew more slowly and exhibited higher mortality rates * This study may lack ecological validity -There were higher amounts of Bt pollen on the leaves than would be found naturally (e.g. rain would diminish build up) -Larva were restricted in their diet (in the field, larva could feasibly avoid eating pollen dusted leaves) Second study, Field condition: * Compared the survival rate of monarch butterflies based on proximity to Bt corn fields * There was no significant increase in mortality when monarch larva were placed in or near an actual Bt corn field * From this it was concluded that exposure to Bt pollen poses no significant risk to monarch butterfly populations

Answer 7

A group of genetically identical organisms. A group of cells derived from a single parent cell.

Answer 8

Plants: * Tubers - the swollen tips of underground stems are storage organs in plants (potatoes!) * Plant stem Cuttings – many but not all plants can be cloned by taking a cutting and immersing it in water. * Runners like strawberry plants grow horizontal stems with plantlets that can grow roots and become independent clones. * Bulbs - a single bulb of garlic, when planted will grow leaves that will result in groups of clone bulbs Animals: * Monozygotic twins are naturally-occuring clones, epigenetics make it look different. * Starfish can regenerate a whole body from a single leg. * Asexual reproduction such as binary fission.

Answer 9

Many common plants root easily from stem cuttings producing full-grown (clone) plants quickly. * Examples of factors that can be investigated: * Substrate - water, type of soil * Number of leaves on the stem * Length of stem cut * Effectiveness of commercial rooting powders * Covering with a plastic bag (to reduce transpiration) * How the stem is cut * Proximity of a node (point of branching) to the base of the stem

Answer 10

Embryos can split and then continue to develop separately to form identical twins. This is possible because in embryonic development the cells are still unspecialized and can become any type of cell. Below shows this process being done artificially: using a pipettes cells are extracted from the embryo (A) and implanted into an embryo (to be implanted into a surrogate mother). (B). | see doc for photo if need be

Answer 11

* Cloning an organism with desired traits is problematic as a developed organism consists of specialized cells which are multipotent, unipotent, or cannot divide at all. * For a clone to develop from somatic (diploid body) cells these cells need to be induced to become pluripotent (cells capable of dividing to become any type of cell). * John Gurdon, in 1958, transplanted the nucleus of a (specialized diploid) tadpole intestinal cell into an enucleated (nucleus removed) frog egg.This created tadpoles that were genetically identical to the original tadpole. This is called somatic-cell nuclear transfer (SCNT) Creating a genetically identical organism through transfer of a differentiated diploid nucleus. Dolly the sheep was the first successful cloning of a mammal from a differentiated somatic cell. Dolly came from Finn Dorset male sheep and Scottish blackface female sheep. How was dolly created (and any other SCNT process): * Remove and culture the desired somatic cell (non-gamete). * Remove a differentiated diploid nucleus from the individual’s cultured cells. * Collect and enucleate a donor unfertilized egg cell. * Fuse together the diploid nucleus into the enucleated egg cell using a zap of electrical current. * The egg is then stimulated to divide and develop into an embryo by the electrical current. * Implant the egg into the endometrium of a surrogate mother for gestation. * The newborn will be genetically identical to the donor nucleus parent.

Topic 3.5 & Some Topic 7: Biotechnology and Genetic Modification/Nucleic Acids Flashcards

DP2- U2- Molecular Genetics (36 cards)