Genome Projects

• In Europe, viruses have infected a large number of frogs of different species. The viruses are closely related and all belong to the Ranavirus group. Previously, the viruses infected only one species of frog. Suggest and explain how the viruses became able to infect other species of frog?

  1. Mutation in the viral DNA
  2. Altered tertiary structure of the viral attachment protein
  3. Allows attachment protein to bind to receptors of other species
• Name three techniques the scientists may have used when analysing viral DNA to determine that the viruses were closely related?

  1. DNA fingerprinting
  2. Polymerase chain reaction
  3. Gel electrophoresis
• Determining the genome of the viruses could allow scientists to develop a vaccine. Explain how?

  1. The scientists could identify the proteome
  2. They could then identify potential antigens to use in the vaccine
• What is meant by a genome?

  1. All the DNA in a cell/organism
• What is a DNA probe?

  1. (Short) single strand of DNA
  2. Bases complementary with DNA
• Describe how the DNA is broken down into smaller fragments?

  1. Restriction endonuclease
  2. Cut DNA at specific base sequence
• What is meant by a non-coding base sequence?

  1. Does not code for amino acid
• Give the name of the method used to clone DNA in vitro?

  1. Polymerase chain reaction
• Doctors can use the method with DNA probes to identify the specific strain of M. tuberculosis infecting a patient. This is very important when there is an outbreak of a number of cases of tuberculosis in a city. Suggest and explain why it is important to be able to identify the specific strain of M. tuberculosis infecting a patient?

  1. To see if strain is resistant to any antibiotics
  2. So can prescribe effective antibiotic
• A scientist produced transgenic zebrafish. She obtained a gene from silverside fish. The gene codes for a growth hormone (GH). She inserted copies of this GH gene into plasmids. She then microinjected these recombinant plasmids into fertilised egg cells of zebrafish. Describe how enzymes could be used to insert the GH gene into a plasmid?

  1. Restriction endonucleases/enzymes cuts plasmids
  2. Ligase joins DNA and plasmids
• Describe the roles of two named types of enzymes used to insert DNA fragments into plasmids?

  1. Restriction endonucleases - Cut plasmids
  2. Ligase - Joins DNA to plasmid
• The soybean cells were screened for the presence of the P34 protein. This process involved the use of gel electrophoresis to separate proteins extracted from soybean cells. Suggest two features of the structure of different proteins that enable them to be separated by gel electrophoresis?

  1. Charge
  2. Different R groups
  3. Mass of polypeptide
• Explain the role of reverse transcriptase in RT-PCR?

  1. Produces cDNA using mRNA
• Explain the role of DNA polymerase in RT-PCR?

  1. Joins nucleotides to produce complementary strands of DNA
• Any DNA in the sample is hydrolysed by enzymes before the sample is added to the reaction mixture. Explain why?

  1. To remove any DNA present
  2. As this DNA would be amplified
• Suggest one reason why DNA replication stops in the polymerase chain reaction?

  1. Limited numbers of primers/nucleotides
• Scientists have used the RT-PCR method to detect the presence of different RNA viruses in patients suffering from respiratory diseases. The scientists produced a variety of primers for this procedure. Explain why?

  1. Base sequences differ
  2. Different complementary primers required
• Describe and explain how the polymerase chain reaction (PCR) is used to amplify a DNA fragment?

  1. Requires DNA polymerase, DNA nucleotides and primers
  2. Heat to 95 degrees to break hydrogen bonds and separate strands
  3. Reduce temperature (to 65 degrees) so primers bind to DNA
  4. Increase temperature (to 75 degrees), DNA polymerase joins nucleotides
• Explain the shape of the curve in a PCR graph?

  1. Doubles each cycle to produce exponential increase
  2. Plateaus as no more nucleotides/primers