Virus Structure and Classification

Question 1

Background and Significance of viruses

Answer 1

• all forms of life have viruses
• viruses and their hosts have co-evolved
• viral diseases have altered our history, ie AIDS, smallpox, influenza
• many of the concepts and tools of molecular biology have been derived from the study of viruses and their host cells
• > 4,000 viruses identified

Question 2

Viruses as Filterable Agents

Answer 2

• homogenize the tissue
• then concentrate it through a filter- 220nm
• bacteria were trapped by the filter (filter becomes infection), viruses were not (filtrate remains infectious)

Question 3

Virus size

Answer 3

• virsuses too small to be seen with light microscopes
• they are about 10^-7 - 10^-8
• requires tissue growth

Question 4

Properties of viruses

Answer 4

• viruses are associated with all life forms
• viruses are obligate intracellular parasites
• definition of a virus: A capsid-encoding organism
• capsid: protein shell that encapsulates the nucleic acid genome
• virion: the particle encoded by a virus genome

Question 5

Virus genomes are modular

Answer 5

• all viruses have 3 basic gene modules
  1) capsid proteins
  2) the replicon
  3) Host interacting factors - multifunctional proteins that interact with the host, usually non structural because they are left behind in the infected cell and not packaged into the virion

Question 6

Virus Structure

Answer 6

• helical or Icosahedral or complex symmetry capsid
• the capsid shape and genome type are independent
• enveloped virions obtain a lipid bilayer from the host cell
• naked virions lack an envelope

Question 7

Virus Classification

Answer 7

Host Cell (Kingdom)

• Eukaryotic or Prokaryotic
• Plant, insect, animal

Genome Type:

• RNA or DNA
• Single or double stranded

Virion Structure

• enveloped or naked
• helical, isosahedral or complex

Question 8

Virion Componenets

Answer 8

-Genome segments
-Nucleocapsid- protein that coats genome
-capsid or core
-tegument- the proteins around the capsid layer
-matrix
-envelope
-glycoprotein
spike or fiber

Question 9

Virus survival strategy

Answer 9

1- the genome encodes a capsid that protects it outside the cell

2- the genome contains information for infecting a cell, replicating the genome, intracellular survival, and assembling virions

3- transmission to a new host is required to maintain the virus as a species

Question 10

Adenovirus

Answer 10

• viral dsDNA
• icosahedral
• naked virus
• has fibers around outside
• Core proteins V, VII, and u, proteins VI and IX, protease, terminal protein

Question 11

Poxvirus

Answer 11

• brick shaped
• enveloped
• outer and inner membrane
• dsDNA

Question 12

Influenza virus

Answer 12

• enveloped
• helical
• segmented RNA
• HA and NA
• RNA polymerase

Question 13

Retrovirus

Answer 13

• integrase, protease, reverse transcriptase
• gp120, gp41
• capsid shape changes from immature to mature
• enveloped
• dsRNA

Question 14

Herpesvirus

Answer 14

• enveloped
• envelop proteins
• tegument- lots
• dsDNA
• isosahedral