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What is the polymerase chain reaction (PCR)?
Polymerase chain reaction is a process used to increase the number of units of a specific DNA sequence by repeated cycles of synthesis using the enzyme DNA polymerase and specific primers.
Briefly outline the steps in polymerase chair reaction.
- Cycle 1: Desired DNA section is targeted. DNA is heated to separate the double helix into single strands. Mixture is cooled to allow the primers (short pieces of synthetic single-stranded DNA to bind to the ends of the genes.) DNA polymerase and free nucleotides are added and the DNA polymerase copies the DNA strands, starting with the primers. Cycle 1 yields 2 molecules.
- cycle 2: Mixture is heated and the process is repeated. Cycle 2 yields 4 molecules.
- Cycle 3: Process is repeated and yields 8 molecules.
- Cycle 4: Process is repreated and yield 16 molecules.
Outline what happens in gel electrophoresis.
Gel electrophoresis is a process used to separate nucleic acids or proteins that are different in particular physical properties, e.g. size and/or electrical charge. A sample of the macromolecule mixture is placed at the cathode end of a gel. When the current is switched on, the molecules move in the gel depending on their size and electrical charge. Small fragments move more easily than large fragments.
Identify uses of gel electrophoresis.
Gel electrophoresis is used to study DNA samples, e.g. in DNA profiling (DNA fingerprinting), to identify particular individuals. Gel electrophoresis can also be used in genetic screening and the diagnosis of genetic disorders, e.g. the process can distinguish between then normal β-haemoglobin gene and the sickle-cell mutation on the β-haemoglobin gene.
Discuss the importance of DNA profiling in forensic investigations and paternity suits.
DNA evidence collected at a crime scene can provide evidence for a range of suspects. DNA evidence has also been used to solve previously unsolved crimes and to exonerate individuals who were wrongly convicted and imprisoned. In paternity cases, DNA profiling can match the DNA of a child to the mother and suspected father to prove paternity. The DNA fingerprint of everyone, except identical twins, is unique.
What was the human genome project?
The Human Genome Project (HGP) was an international program to map all the genes in the human genome. The idea was conceived in the 1980s after Frederick Sanger developed DNA sequencing techniques in the mid 1970s. The complete human genome sequence was finished in 2003.
Discuss three consequences of completing the DNA sequencing for the human genome.
- 1. An understanding of specific base sequences and gene expression has improved understand of how particular changes in the coding cause specific effects. This has led to a better understanding of genetic disorders.
- 2. Being able to identify specific genes, e.g. gene to produce human insulin, has meant that synthetic human hormones have been able to be made in greater quantities to assist people with specific disorders.
- 3. Genetic screening - an understanding of the sequences that cause genetic disorders has led to the development of genetic tests to identify specific diseases, e.g. sickle-cell anaemia.
Define genetic engineering.
Genetic engineering is the deliberate manipulation of genetic material for a specific purpose.
What is meant by the statement 'the genetic code is universal'?
The genetic code refers to the codon codes for particular amino acids. The code for a particular amino acid is the same in every organism. Thus the genetic code is universal.
Outline why it is possible to transfer genetic information from one species to another?
Genetic engineering techniques have made it possible to locate and extract a specific gene from a particular species. Because the genetic code is universal, this extracted DNA fragment can be inserted into the genetic code of another species. This means that the transgenic species has an unchanged DNA sequence which can produce a particular polypeptide, e.g. the gene for making human insulin has been inserted into bacterium.
Outline the difference between restriction enzymes and ligase enzymes.
A restriction enzyme (restriction endonuclease) are enzymes that cut DNA sequences at particular nucleotide sequences. Ligase enzymes catalyse the joining of segments together, e.g. DNA ligase seals cuts in the backbone of one strand of a DNA double helix. Both restriction enzymes and ligase enzymes are used extensively in genetic engineering.
Outline how enzymes are involved in gene insertion into a plasmid.
Restriction enzymes are used to cut the DNA of interesting and to cut the bacterial plasmid. The enzyme will cut at the same restriction site. The cut plasmids and DNA fragments are mixed and some joini by base pairing. DNA ligase is used to seal the attachments to form a recombinant plasmid. Replication produces more copies of the recombinant bacteria with a required gene inserted into a plasmid.
What is the Ti plasmid?
The Ti plasmid is a plasmid from the soil bacterium Agrobacterium tumefaciens. A section of the Ti plasmid, known as the T DNA section, can be inserted from the bacterium into a plant host. Agrobacterium tumefaciens can transfer diseases into susceptible host species.
Discuss why the Ti plasmid is important in the production of transgenic plants.
Scientists can use the Ti plasmid from Agrobacterium tumefaciens as a vector to produce transgenic plants. A version of the Ti plasmid that does not cause disease is used. Recombinant Ti plasmids can introduce desired characteristics into the host plant cells, e.g. to make the plant herbicide or pest resistant.
Summarise information about a transgenic animal and a transgenic plant.
- Transgenic animal:
- - Name: Salmon
- - Gene inserted: Gene coding for the protein bGH - bovine growth hormone has been insterted into the salmon.
- - Benefit: Larger, faster growing fish.
- - Concern about use of transgenic species: The cultured fish are kept in ponds. If they escaped into the surrounding ecosystem they could upset the natural balance and have a detrimental effect on other populations.
- Transgenic Plant:
- Name: Cotton
- Gene inserted: Gene from the bacteria Bacillus thuringlensis (Bt) that produces a toxin to kill attacking insects such as boilworm. Produces Bt cotton.
- Benefits: Protection against insect attack.
- Concern about use of transgenic species: there are several ways in which the Bt cotton could disrupt natural ecosystems, e.g. pollen from Bt plant may fertilise closely related species and the gene will enter the food chain. This could lead to the death of other insects and an altered balance in population distribution and abundance. Also constant exposure to any selection pressure leads to natural selection and evolution leads to resistant strains of the insect.
A clone is a genetically-identical organsims produced through non-sexual means.
Define therapeutic cloning.
Therapeutic cloning is the use of a somatic cell from a multicellular organism to produce cells/tissue/organ to assist people suffering particular medical problems, e.g. grow new skin for a skin graft for a burn victim.
Therapeutic cloning is a controversial issue. Explain why many people have ethical concerns about this development in genetics.
- Ethical issues related to therapeutic cloning involves:
- 1. Use of embryonic stem cells - the somatic cells which can be used to differentiate into a variety of cells/tissues/organs are extracted from embryos (embryonic stem cells are totipotent). The embryonic stem cells are currently donated by patients undergoing fertility treatment. The removal of the stem cells destroys the embryo. Thus there are ethical issues about the use of embryonic stem cells.
- 2. Potential use to clone humans - many people fear the technology will be used to clone people
- 3. Abnormalities in cloned individuals - not only do many clones not survive the process, many of the individuals that are born have some form of abnormality. Ethical issues arise about the disposal of the individuals that do not survive and the reduced life expectancy of the clones.