Unit 2 - Viruses

• What is a virus

  A non-cellular particle made up of genetic material and protein coat that can invade living cells.
• What is a parasite

  An organism that depends entirely upon another living organism for its existence in such a way that it harms that organism.
• Is a virus living or non-living

  It is considered to be both: Living because genetic material is in viruses, and because evolutionary history shows similarities in protein folds of various cells and viruses. Non-living because viruses cannot grow, develop, reproduce, obtain and use energy independently.
• What is the structure of a virus

  A virus has an inner core containing genetic material of either DNA or RNA. Virus structures vary greatly because they are adapted to their host cells.
• What is a capsid

  An outer protein coat of a virus.
• What do the arrangements of proteins in the capsid of a virus determine

  The virus' shape and what cell can be infected (and how).
• How many genes do viruses have

  Can have anywhere from 4 to several hundred genes.
• How big are viruses


  20 to 400 nanometers
• How are viruses specific

  They are species specific → plant viruses only infects plants. cell-type specific or only infect a few organisms - west nile virus infects horses humans and birds.
• What are bacteriophage

  Viruses that infect bacteria
• What is the bacteriophages tail region made of and what does it do

  An elaborate protein structure. It binds the bacteriophage to the hosts cell, to inject genetic material in the host cell.
• What is a viral infection

  When a virus has successfully introduced their genetic material into a host cell.
• What is the lytic cycle


  When a virus infects a living host cell in order to reproduce.
• How many steps does the lytic cycle have

  5
• What is the first step of the lytic cycle

  Attachment (like velcro)
• What is the second step of the lytic cycle

  Entry
• What is the third step of the lytic cycle

  Replication (using hijacked cell)
• What is the four step of the lytic cycle

  Assembly (of the new virus)
• What is the fifth step of the lytic cycle

  Lysis and release
• What is lysis

  The disintegration of a cell by rupture of the cell wall or membrane.
• How do viruses activate

  By chance contact with the right host cell.
• What happens when viruses are activated

  They will inject their genetic material into their host cell.
• What is replication

  When viruses use the materials of the host cell to make thousands of copies of its own protein coat and DNA, and the host gets full of hundreds of viral DNA molecules.
• What is assembly

  When new virus components are assembled into a whole virus structure.
• What is lysis

  A new virus particles are assembled and the infected cell bursts (lyses), Hundreds of new virus particles are released and may now infect other cells.
• What is a lytic infection

  When a host cell lyses and is destroyed.
• How many steps does the lysogenic cycle

  There are 4 steps
• What are the steps of the lysogenic cycle

  Attachment, Entry, Pro-virus formation, Cell division
• What is attachment and entry in the lysogenic cycle

  By chance contact, viruses will attach onto the right host cell. When activated, viruses will inject their DNA into their host cell.
• What is provirus formation

  Viral DNA is inserted into the DNA of the host cell, and is now called a provirus.
• What is the provirus of a bacteriophage called

  Prophage.
• What does cell division look like in the lysogenic cycle

  A provirus may not affect the function of the host cell, however, every time a host cell reproduces, the provirus is replicated along with the host cell's DNA.
• How long does the lysogenic cycle continue for

  Many years
• What happens when a lysogenic virus' virus gene becomes active when in provirus form

  It removes itself from the host DNA and will enter the lytic cycle.
• What factors might activate a virus to enter the lytic cycle


  Sudden changes in temperature, Availability of nutrients, Weakened immune system, Stress and anxiety
• What are retroviruses

  A special type of virus that contains RNA, and inserts viral RNA into the host cell. It means backwards virus.
• What is reverse transcription

  An enzyme called reverse transcriptase, will convert viral RNA to viral DNA. There is no DNA proofing.
• Does viral RNA mutate

  Yes, often and becomes resistant to pharmaceuticals
• What does the viral RNA act like

  A lysogenic virus and is inserted into the host cell's DNA becoming a provirus.
• What is AIDs caused by

  A retrovirus called HIV