viruses

• What is the size range of viruses?

  10 nm to 300 nm
• What surrounds the nucleic acid in viruses?

  A protein coat called capsid
• What types of nucleic acid can viruses have?

  DNA or RNA
• What are the characteristics of bacteriophages?

  • Commonly called phages
  • Normally have a DNA core
  • Parasitic on bacteria
  • Viral DNA codes for new proteins
  • Bacterial cell is destroyed upon release
• How do bacteriophages replicate inside host cells?

  They code for new proteins and replicate DNA
• What is the structure of HIV?

  • RNA core
  • Protein coat
  • Lipid bilayer with glycoprotein
• What enzyme does HIV deliver into the host cell?

  Reverse transcriptase
• What process does reverse transcriptase catalyze in HIV?

  Synthesis of DNA from RNA
• What are retroviruses?

  Viruses that use RNA to make DNA
• What type of cells does HIV invade in humans?

  Helper T-cells
• What happens to the immune system as T-cells are destroyed by HIV?

  The immune system becomes critically compromised
• What are the key differences between bacteriophages and HIV?

  • Different shapes
  • Phages have tail fibres
  • HIV has a phospholipid bilayer
  • Glycoproteins present in HIV
  • Bacteriophages usually contain DNA
• What is the function of tail fibres in bacteriophages?

  To attach the virus to bacterial cells
• What is reverse transcriptase's role in HIV?

  It synthesizes DNA from RNA
• What are the two techniques used in cell practical work?

  1. Homogenisation (cell fractionation)
  2. Centrifugation
• What is homogenisation in cell fractionation?

  Breaking up and mixing material for uniformity
• What tools can be used for homogenisation?

  Mortar and pestle or blender
• What happens during centrifugation?

  Larger particles sediment at the bottom
• What is found in the pellet after centrifugation of liver tissue?

  Nuclei
• Why is counterbalancing important in centrifugation?

  To ensure even distribution of forces
• How can specific organelles be isolated during centrifugation?

  By altering speed and time of centrifugation
• What should you be able to do with cell sections under a microscope?

  • Prepare sections on a slide
  • View using a light microscope
  • Draw individual or groups of cells
• What is the purpose of using stains in microscopy?

  To differentially stain cell components
• Name two examples of stains used in microscopy.

  Safranin and methylene blue
• Why are viruses considered not true cells?

  They lack cytoplasm and organelles
• Why are viruses considered inert?

  They do not function without a living cell
• What is a key similarity between bacteriophages and HIV?

  Both are very small and non-motile
• What do bacteriophages have that HIV does not?

  Tail fibres attached to a base plate
• What is the significance of reverse transcriptase in HIV?

  It allows RNA to be converted to DNA
• What will be covered in detail at A2 regarding viruses?

  Transcription and protein synthesis