Properties of virus




Properties of virus

Some general properties of virus are;

1. Size:

  • The size of virus ranges from (20-300) nm in diameter.
  • Parvovirus is the smallest virus with size 20nm whereas Poxvirus is largest being 400nm.

2. Shape:

  • The overall shape of virus varies in different groups of virus.
  • Most of animal viruses are spherical shape, Pox virus is rectangular shape, TMV is rod shape, Poliovirus is bullet shape etc
  • Some virus are irregular and pleomorphic in shape.

3. Symmetry:

  • Morphological protein subunits of capsid are arranged together to from a symmetrical structure of the virus.
  • Two basic symmetry are recognized in virus, they are helical symmetry and icosahedral symmetry.
  • In some virus, symmetry is more complex, which is other than helical or icosahedral.

4. Structure and Chemical composition:

i. Genome:

  • Viral genome or nucleic acid  contains either DNA or RNA but not both.
  • The genome can be either ds DNA or ss DNA or ds RNA or ss RNA
  • The genome can exist as single piece or segmented. Eg, Influenza virus contains 8 segments of ss RNA genome.
  • The genome may be linear or circular. Most virus possess linear genome except Papova virus which contains circular ss DNA.
  • Genome helps replication of virus in host cell.

ii. Capsid:

  • Capsid is the outer shell of a virus.
  • It is chemically a viral protein.
  • Capsid is composed of capsomere.
  • Structure of capsid gives the symmetry of virus.
  • Capsid protects the nuceic acid and also helps in attachments on host cell surface during infection.

iii. Envelope:

  • Some virus contains phospholipid bilayer known as envelope.
  • Virus lacking envelope is called naked virus.
  • Envelope is a lipid bilayer which is acquired from host cell membrane

iv. Glycoprotein spike:

  • Envelope of some virus contains viral coded spike projected outside the envelope called glycoprotein spike or peplomers.
  • Glycoprotein spike are viral coded protein with carbohydrate head.
  • Glycoprotein spikes is an important antigenic structure.
  • Neuraminidase and Haemagglutinin are glycoprotein spikes which helps in virus attachment to cellular receptor on host cell to establish infection.

v. Enzymes:

  • Some virus possess their own enzymes.
  • Retrovirus possess reverse transcriptase

5. Viral replication:

  • Virus only replicates inside host cell

6. Metabolism:

  • Viruses are metabolically inert outside host cell.
  • They are also called as obligate intracellular parasite

7. Resistance:

i. Temperature:

  • Most viruses are heat labile.
  • Viruses are inactivated by heating at 60°C for 30 minutes or 100°C for few seconds.

ii. Cold:

  • Viruses are stable and resistant to cooling.
  • Virus can be stored for long duration at -40°C to -70°C by lyophilization or freeze drying.

iii. Radiation:

  • Both non-ionizing and ionizing radiation can kill virus.
  • UV rays causes pyrimidine dimer formation while ionizing radiation eg, X-rays causes lethal break of viral genome.

iv. Organic solvent:

  • Chloroform, ether and bile salt can destroy all viruses by lipid solubiliation.

v. Disinfectant:

  • Most viruses are destroyed by oxidizing agents such as chlorine, H2O2, iodine etc.
  • Many viruses are resistant to phenol and chlorination. The phenol and chlorine do not always inactivates enterovirus, particularly if they are present in faecal materials.

vi. Antibiotics:

  • Viruses are resistant to antibiotics.

Properties of virus