Viruses

• How do viruses replicate

  infecting a host cell by injecting it’s genetic material and replicating inside it
• How are new viruses made in a host cell

  The genetic material of the virus replicates and uses the host cells nutrients and energy sources to assemble new virus particles
• what happens when a replicating virus uses the host cells nutrients and energy sources

  prevents the cell from carrying out normal metabolism
• what happens after new viruses are made in a host cell

  the host is destroyed and the virus particles are released, infecting new cells
• what are viruses which infect bacteria cells called

  bacteriophages
• what Re the two types of replications bacteriophages undergo?

  lytic and lysogenic
• Simple structure


  A virus consists of a protein coat (capsid) and a genetic material (either DNA or RNA).
• Specific host


  A virus is specific to certain hosts, such as animals, plants, or bacteria.
• typical features of a virus:

  • glycoprotein spikes
  • viral envelopes
  • genetic material
  • reverse transcriptase
  • capsid
• what are glycoprotein spikes in viruses

  glycoprotein receptor spikes on the viral envelope help them to attach to the surface of the host cell
• what do some viruses have instead of glycoprotein spikes

  long tail fibres
• what are viral envelopes on viruses?

  additional membranes that surround the capsid of some viruses, made of lipoprotein
• what are viral envelopes made of?

  lipoprotein
• what is between the envelope and capsid of a virus?

  a matrix
• viruses are acellular/ non- cellular
• viruses are nucleic acids surrounded by protein
• viruses do not have:

  a plasma membrane, cytoplasm or ribosomes
• viruses are not living as they are metabolically inert until they have invaded host cells
• why do viruses have no metabolic activity?

  they are not detected by bodily cells and therefore can easily pass through cells plasma membrane and infect host cells
• what do viruses cause after infecting a host cell?

  Cell lysis, the metabolic activity in the cell increases with the presence of a virus within it causing the feeling of sickness
• What is the general lifecycle of a virus?

  Attachment, penetration, biosynthesis, maturation, and lysis
• How do viruses identify the cells they attack?

  By recognizing specific surface receptors
• What happens when a virus infects a cell?

  It injects its own genetic material into the cell
• What occurs after the genetic material of a virus replicates?

  Many virus particles are assembled
• What is the morphology of a virus primarily composed of?

  Nucleic acid and a protein coat called a capsid
• What is a procapsid?

  The protein shell that surrounds the nucleic acid before assembly
• What are the three types of virus morphology?

  Helical, icosahedral, and composite
• What is lytic replication in bacteriophages?

  The process where the virus uses the host's nutrients and energy, leading to cell destruction
• What are the stages of the lytic replication cycle of bacteriophages?

  1. Attachment: Phage attaches to the bacterial cell
  2. Penetration: Phage tail punctures the cell wall and membrane
  3. Biosynthesis: Phage DNA is transcribed, and bacterial DNA is degraded
  4. Maturation: Phage components are assembled into mature capsids
  5. Lysis: The bacterial host is destroyed, releasing new viruses
• How long does it take for 200 phages to be assembled in the lytic cycle?

  Approximately 25 minutes
• What are the steps involved in the replication of animal viruses?

  1. Recognition & attachment
  2. Penetration of the host by endocytosis
  3. Uncoating of the viral genome
  4. Synthesis of nucleic acid & proteins
  5. Viral assembly
  6. Release of new viral particles
• What is the lysogenic replication process?

  Viruses incorporate their DNA into the host DNA, which is passed to daughter cells
• What happens under stressful conditions in the lysogenic cycle?

  The phage DNA is excised from the bacterial chromosome and enters the lytic cycle
• What is a prophage?

  The phage DNA that is incorporated into the bacterial DNA
• What is the role of the protein produced during lysogeny?

  It inhibits the lytic cycle and ensures integration of phage DNA into bacterial DNA
• What are the key differences between lytic and lysogenic replication?

  • Lytic replication:
  • Immediate destruction of the host cell
  • Rapid production of new viruses
  • Lysogenic replication:
  • Integration of viral DNA into host DNA
  • Dormant phase before potential activation
• What do viruses lack that is necessary to derive energy?


  Mitochondria
• Why are viruses only classed as living organisms when they infect host cells?


  Because they cannot reproduce on their own
• What happens to host cells after viruses reproduce?


  They are inevitably destroyed
• What are the characteristics that describe viruses as obligate intracellular parasites?


  • Lack mitochondria
  • Cannot reproduce independently
  • Depend on host cells for reproduction
  • Cause destruction of host cells after reproduction