Virus- cell interactions:
Virus- an infectious agent; extremely small, only can be seen by electron microscopy; viruses cannot
be grown outside a cell; replication of a living cell is absolutely dependent on living cells (occurs only
in living cells), they are obligate intracellular parasites
Virus particles do not have mitochondria or ribosomes, they consist of nucleic acid and protein ( DNA
OR RNA cannot be both)
HIV – retrovirus ; virus that is in a different class to the other 4
Virus structure
Electron microscope – the source of illumination is a beam of electrons
Stanley WM (1935) – original discovery of viruses; isolated a crystalline protein possessing the
properties of the tobacco mosaic virus (agent that induces infection)
Crook and Sheffield (1946) – first structure of a virus using electron microscope in a state of
aggregation
Franklin (1955) – Structure of tobacco mosaic virus and DNA; viruses may have very repetitive
structure of their genome
Crick and Watson – demonstrate that the virus genome is able to encode only a small number of
genes, therefore identical proteins must be used to construct a virus particle, therefore giving the
repetitive structure of the virus particle;
, Structural proteins are called capsomeres which assemble to form a capsid around the virus genome
and then the nucleocapsid will have either helical or icosahedral symmetry
TMV – RNA virus
Icosahedron symmetry – regular geometric figure constructed from 20 equilateral triangles
Poliovirus, papilloma virus – non-enveloped
Poliovirus 30nm Papillomavirus 55nm
Virus envelopes are derived from membranes of host cells but modified to contain virus-specifi
glycoproteins
Herpesvirus (icosahedral nucleocapsid 120nm) Influenza virus (helical nucleocapsid 100-200nm)
Virus- an infectious agent; extremely small, only can be seen by electron microscopy; viruses cannot
be grown outside a cell; replication of a living cell is absolutely dependent on living cells (occurs only
in living cells), they are obligate intracellular parasites
Virus particles do not have mitochondria or ribosomes, they consist of nucleic acid and protein ( DNA
OR RNA cannot be both)
HIV – retrovirus ; virus that is in a different class to the other 4
Virus structure
Electron microscope – the source of illumination is a beam of electrons
Stanley WM (1935) – original discovery of viruses; isolated a crystalline protein possessing the
properties of the tobacco mosaic virus (agent that induces infection)
Crook and Sheffield (1946) – first structure of a virus using electron microscope in a state of
aggregation
Franklin (1955) – Structure of tobacco mosaic virus and DNA; viruses may have very repetitive
structure of their genome
Crick and Watson – demonstrate that the virus genome is able to encode only a small number of
genes, therefore identical proteins must be used to construct a virus particle, therefore giving the
repetitive structure of the virus particle;
, Structural proteins are called capsomeres which assemble to form a capsid around the virus genome
and then the nucleocapsid will have either helical or icosahedral symmetry
TMV – RNA virus
Icosahedron symmetry – regular geometric figure constructed from 20 equilateral triangles
Poliovirus, papilloma virus – non-enveloped
Poliovirus 30nm Papillomavirus 55nm
Virus envelopes are derived from membranes of host cells but modified to contain virus-specifi
glycoproteins
Herpesvirus (icosahedral nucleocapsid 120nm) Influenza virus (helical nucleocapsid 100-200nm)
