Mod 6 - Manipulating Genomes Flashcards
What is the total DNA of an individual called? (1)
Genome
Give 2 distinct differences between the genomes of a bacterium (e.g E.coli) and a human. (2)
E. coli has a single circular loop of DNA, with relatively few protein coding genes (4288) mostly organised into operons and in smaller loops called plasmids. There are also some ribosomal RNA and transfer RNA genes. Homo sapiens has rod-shaped chromosomes (23 pairs), each carrying 20 000 to 25 000 genes, and loops of DNA in the mitochondrial matrix.
Genomics is the study of which area if science? (1)
The study and application of genetic and molecular biology techniques to gene mapping and gene sequencing (on the chromosomes or for an entire organism).
State 3 of the different regions un the nuclear DNA of a eukaryote. (3)
Structural genes Non structural genes Ribosomal RNA and transfer RNA genes Regulatory genes Promoters Hypervariable sequences Introns and axons
Apart from nuclear DNA, what other DNA is found in eukaryotic cells? (1)
Mitochondrial DNA within mitochondria
Chloroplast DNA within chloroplast
There are several techniques used in analysis of DNA. Name 4. (1)
PCR
Gel electrophoresis
DNA sequencing
DNA profiling
Explain why a different primer is required for different DNA samples. (2)
The sequence of bases in the primer must match (by complementary base pairing) the DNA sequence at the start of the region of DNA being copied/amplified. Different DNA has different base sequences.
Outline how a sample of DNA may be treated before analysis using gel electrophoresis (2)
The DNA sample is treated with restriction enzymes to ‘cut’ it into small sections
OR fragments are amplified using PCR
OR a dye or a radioactive label is added and the fragments are loaded into the wells in the gel.
Outline the method of carrying out gel electrophoresis (6)
- Pour molten gel (agarose) into electrophoresis tank contains toothed comb to form wells.
- Once set, remove comb and add buffer solution.
- Load sample (containing dye) into wells.
- Connect electrodes to tank and power supply; leave to run until sample is 2cm from the end and then pour away buffer.
- Add stain to make banding visible.
- Rinse and observe.
Explain the basic principle and process used to carry out DNA profiling.
DNA contains a variable number of short tandem repeats; they are unique to each individual.
State the difference between mini satellites (VNTRs) and micro satellites (STRs), and explain why it is better to use microsatellites in DNA profiling. (4)
Minisatellites (variable number tandem repeats or VNTRs) are small sections (10–100 bps) of DNA in structural genes or in the non-structural DNA and are inherited from both parents. These are repeated at various points along the chromosome and can be cut by restriction enzymes.
Microsatellites (STRs) are much shorter sequences of nucleotides (2–5 nucleotides long but repeated 10–30 times) which may be in the non-coding DNA between the structural genes. These are easily identified and more unique as there is more variation between individuals and they are less likely to degrade. Also, only a short length is needed, so DNA profiling works well on a small sample.
In what way does Huntington’s disease involve STRs? (2)
The greater the number of STRs in the gene for the protein huntington, the greater the risk of developing the symptoms of Huntington’s disease in later life.
Explain how a single nucleotide polymorphism (SNP) within a gene might not affect the protein produced during protein synthesis. Give an example of one important role SNPs may play. (2)
It is a variation in one nucleotide. A change in a single base will not affect the gene reading frame so protein synthesis can still occur and a protein can still be produced. It may be the same protein if the nucleotide change still codes for the same amino acid or it may be a different variation of a protein.
Role: act as biological markers of disease; form a large proportion of genetic variation in humans; occur more frequently than mutations.
Why is the genome of a Drosophila fruit fly useful in human genome studies? (2)
The genes involved in development in Drosophila are similar in some ways to those found in other animals including humans. This can be given as a percentage figure of degrees of similarity, which is useful in uncovering evolutionary relationships and ancestry.
Explain role of DNA ligase in genetic engineering. (1)
An enzyme that forms phosphodiester bonds. Can be used to join a gene to a plasmid.
How is a vector used in genetic engineering? (1)
A vector is a structure used to deliver a gene into the host organism as part of genetic engineering.
What is a BAC? (1)
A bacterial artificial chromosome.
What is a liposome? (1)
A vesicle surrounded by plasma membrane.
What is rDNA? (1)
recombinant DNA, formed when DNA from one organism is combined with the DNA of another.
Give correct terms for some of the applications used in genetic engineering: (5)
- Cuts DNA at specific bases sequences
- Anneals or seals the DNA cut ends and forms a phosphodiester bond between them
- Makes cDNA from RNA
- Is used to transfer DNA into the bacterial cells
- May be used to transfer genes into human cells
- Restriction endonucleases
- Ligase enzymes
- Reverse transcriptase enzymes
- Plasmids
- Viruses/liposomes
How does an restriction enzyme identify the position to make a cut in the DNA molecule? (1)
It cuts across the DNA at a specific recognition sequence, comprising a short palindromic sequence of bases.
Describe a sticky end and its importance in annealing. (2)
This is an unpaired ‘overhanging’ sequence of bases on one of the polynucleotide chains. It allows the annealing of another ‘overhanging’ sequence of complementary bases.
What consequence results from the variations in amino acids seen in beef and pork insulin compared with human insulin? (2)
The differences, although in only a few nucleotide base pairs, create a slightly different protein. This difference triggers the human immune system and an immune response.
Outline the steps involved in the process of genetically modifying E. coli to produce commercial quantities of human insulin. (6)
- The mRNA produced from the gene for insulin is extracted from β cells in the pancreas and converted to DNA using reverse transcriptase.
- Sticky ends are added to the cDNA.
- A plasmid from E. coli is extracted and cut using a restriction enzyme.
- The cut plasmids are mixed with the cDNA with complementary sticky ends.
- A ligase enzyme anneals the cDNA and cut plasmid.
- Plasmids are added to new bacteria treated with calcium followed by a cold shock.
- Transformed bacteria are identified and pure continuous cultures of them are set up.
- Insulin, produced in large quantities by the transformed bacteria, is harvested.
GM crops have been used to improve a number of features, such as resistance to insect and fungal pests. Give examples of GM crops cultivated for human health reasons (2)
- golden rice that provides increased levels of vitamin A precursors
- GM bananas that act as a vaccine for hepatitis B.
Giving advantages of the use of GM crops in today’s world. (5)
- resistance to disease, pests, drought and herbicides improves crop production and reduces losses
- an increase in nutritional value
- production of medicines/vaccines
- allows production of crops that allow for climate change faster than traditional selection processes
- allows large-scale food production to keep pace with the increase in human population growth.
Discuss objections to the use of GM cops in today’s world. (6)
- may be too expensive for farmers in developing countries
- possible transfer of antibiotic-resistant genes or herbicide-resistant genes into other organisms
- could lead to antibiotic-resistant pathogens or weeds super resistant to herbicides
- the genomes of crop plants may be altered by introduction of foreign genes
- mutations in foreign genes could cause unknown effects in crop plants
- possible creation of new pathogenic viruses
- loss of genetic diversity
- no economic advantage to farmers as they still need to use herbicides and pesticides and cannot keep seed for replanting as the crops do not breed true.
Suggest why approval hasn’t been given in the UK for development of GM animals for human consumption. (2)
- Unspecified public concerns regarding use of GM animals;
- full effect of GM on the whole genome of the animals is unknown;
- effect of GM animals in the food chain untested;
- lack of public trust of scientists.
State one use and one application of GM mice and GM viruses for hum medical purposes. (2)
Mouse:
Use - production of monoclonal antibodies.
Application - Detection and directed cancer treatment.
Virus:
Use - modified to carry and deliver genes.
Application - Gene therapy
Define gene therapy. (1)
Inserting genes into cells of an organism to correct or repair a genetic problem. Usually a dominant allele is added into the cells where an individual has two recessive alleles for the gene.
What is the difference between somatic gene therapy and germ-line gene therapy? (2)
Somatic gene therapy: a gene is inserted into body cells of an organism so only those cells benefit. Usually this must be repeated at regular intervals as the cells will die and not pass on the gene. If inserted into a stem cell it may offer longer-term treatment.
Germ-line gene therapy: a gene is inserted into reproductive cells of an organism. In this case the gene will be passed on to the gametes and so to any offspring.
What principles are involved in the practical activity of electrophoresis? (2)
The phosphate groups give DNA fragments a negative charge, so DNA fragments migrate to the anode of an electric field.
Pores in the agarose gel allow fragments to migrate, with the smaller fragments moving faster, and so further, than the larger fragments.
Explain how the capillary method (like G.E.) increases the speed of separation and detection compared with the Sanger method. (2)
The DNA fragments are detected as they migrate through agarose gel in capillary tubes, so there is no need to wait until the end of electrophoresis to begin analysis. There are many capillary tubes—96 is the number frequently used—so more ‘runs’ can be performed at the same time. Analysis is by direct feed into a computer, so the output is faster.
Give 2 ways in which a retrovirus differs from other viruses. (2)
A retrovirus contains a core of RNA instead of DNA and an enzyme called reverse transcriptase.
How does a retrovirus affect the organism it infects? (2)
The virus infects the organism’s cells. Its RNA and enzyme enter the nucleus where DNA is manufactured from viral RNA suing the host cell’s mechanism and the enzyme. The resulting DNA is incorporated into the host DNA where it can lie dormant for many years before becoming activated.
