Exam Questions

• Describe how HIV is replicated. (4)

  1. Attachment proteins attach to receptors on helper T lymphocyte.
  2. RNA enters cell.
  3. Reverse transcriptase converts RNA to DNA.
  4. Viral proteins produced.
  5. Virus particles assembled and released from cell.
• Describe how the human immunodeficiency virus (HIV) is replicated once inside helper T cells (TH cells). (4)

  1. RNA converted into DNA using reverse transcriptase.
  2. DNA incorporated into helper T cell DNA.
  3. DNA transcribed into HIV mRNA.
  4. HIV mRNA translated into new viral proteins for assembly into viral particles.

  Note: here, the mark scheme requires more detail about the transcription and translation stages, as no detail is needed about how HIV enters the helper T cell.
• Describe how a phagocyte destroys a pathogen present in the blood. (3)

  1. The phagocyte engulfs the pathogen.
  2. A vesicle called a phagosome is formed, which fuses with a lysosome.
  3. The lysosome releases enzymes into the phagosome, which digest/hydrolyse the pathogen.
• What is the role of the disulfide bridge in forming the quaternary structure of an antibody? (1)

  It joins two different polypeptides together.
• Explain how HIV affects the production of antibodies when AIDS develops in a person. (3)

  1. Fewer antibodies are produced.
  2. Because HIV destroys helper T cells when it replicates.
  3. So few B cells activated.
• Determining the genome of the viruses could allow scientists to develop a vaccine. Explain how. (2)

  1. The scientists could identify the proteome.
  2. They could then identify potential antigens to use in the vaccine.
• How do lymphocytes respond to a vaccination against a pathogen? (3)

  1. B cell antibody binds to viral complementary antigen.
  2. B cell divides by mitosis.
  3. Plasma cells produce monoclonal antibodies against the virus. 4. B cells produce memory cells.
• What is a monoclonal antibody? (1)

  Antibody produced from cloned B cells.
• Describe the role of antibodies in producing a positive result in an ELISA test. (4)

  1. First antibody is complementary in shape to antigen and binds to it.
  2. Second antibody with enzyme attached is added.
  3. Second antibody attaches to first antibody.
  4. Substrate added and colour changes.
• Describe and explain the role of antibodies in stimulating phagocytosis. (2)

  1. The antibodies bind to the antigens.
  2. The antibodies cause agglutinatin.
• Describe how phagocytosis of a virus leads to presentation of its antigens. (3)

  1. Phagosome fuses with lysosome,
  2. Virus destroyed by lysozymes/hydrolytic enzymes.
  3. Antigens from virus are displayed on the cell membrane.
• Describe how presentation of a virus antigen leads to the secretion of an antibody against this virus antigen. (3)

  1. Helper T cell binds to the antigen on the antigen presenting cell.
  2. This helper T cell stimulates a specific B cell.
  3. B cell clones
• What is an antigen? (2)

  A foreign protein that stimulates an immune response.
• What is an antibody? (2)

  A protein specific to an antigen that is secreted by plasma cells.
• Describe the difference between active and passive immunity. (5)

  1. Active involves memory cells, passive does not.
  2. Active involves production of antibody by plasma cells.
  3. Passive involves antibody introduced into body from outside.
  4. Active long term, because antibody produced in response to antigen.
  5. Passive short term, because antibody given is broken down.
  6. Active can take time to develop work, passive fast acting.