virus stacture

1. DEPARTMENT OF VETERINARY MICROBIOLOGY
Rajasthan University of Veterinary & Animal Sciences, Bikaner
Presentation on – Virus
Structure
Submitted to-
Prof.(Dr.) S. Meharchandani
Submitted by-
Chanderkant Suthar
M.V.Sc. 1st year

2. Basic structure consists of protein shell
(capsid) surrounding nucleic acid core
Acellular /non-cellular
Obligate intracellular parasite
Ultramicroscopic ( 20-300nm)
Contain RNA/DNA
Inactive macromolecules outside host

3. 1. Nucleic acid (DNA or DNA)
2. Protein coat(capsid)
3. Some are enclosed by an
envelop
4. Some virus having spike

5.  RNA or DNA (single-stranded or double-
stranded; non-segmented or segmented;
linear or circular
 if genome is single stranded RNA, can it
function as mRNA.

6.  All viruses have capsids- protein coats that
enclosed and protect their nucleic acid .
 Each capsids is constructed from identical
subunit called capsomeres made of protein
 The capsid together with nucleic acid are
nucleoscapsid

8. ◦ Packaging and protecting nucleic acid
◦ Host cell recognition
 Protein on coat or envelope “feels”
or “recognizes” host cell receptors
◦ Genomic material delivery
 Enveloped: cell fusion event
 Non-enveloped: more complex
strategies & specialized structures

10.  An icosahedron is defined as being made up
of 20 equilateral triangular faces arranged
around the surface of a sphere.
 the subunits are arranged in the form of a
hollow, quasi spherical structure, with the
genome within

11. They display 2-3-5 fold symmetry as follows:
 an axis of 2 fold rotational symmetry through the
center of each edge.
 an axis of 3 fold rotational symmetry through the
center of each face.
 an axis of 5 fold rotational symmetry through the
center of each corner.

12.  12 vertices
 20 faces
(equilateral triangles)
 5-3-2 symmetry axes
 60 identical* subunits
in identical environments
can form icosahedral shell

13.  Since proteins are not equilateral triangles,
each face of an icosahedron contains more
than one protein subunit. The simplest
icosahedron is made by using 3 identical
subunits to form each face, so the minimum #
of subunits is 60 (20 x 3)..
 Many viruses have too large a genome to be
packaged.
 The total number of subunits can be defined as
60 X N, where N is sometimes called
the Triangulation Number, or T. Values for T of
1,3,4,7,9, 12 and more are permitted.

14. Spherical viruses have icosahe

15.  A helix can be defined by two parameters, its
amplitude (diameter) and pitch, where pitch is
defined as the distance covered by each turn
of the helix.
 P = m x p, where m is the number of
subunits per turn and p is the axial rise per
subunit
 For Eg.TMV, m = 16.3 and p= 0.14 nm, so
P=2.28 nm

16.  This structure is very stable, and can be
dissociated and re-associated readily by
changing ionic strength, pH, temperature,
etc.
 The interactions that hold these molecules
together are non-covalent, and involve H-
bonds, salt bridges, hydrophobic interactions,
and vander Waals forces

17.  Helical nucleocapsids
are characterized by
length, width,pitch of
the helix, and number
of protomers per
helical turn
 Helical morphology is
seen in nucleocapsids
of many filamentous
and pleomorphic
viruses

18.  viruses with asymmetrical structures are
referred to as "complex. " These viruses
possess a capsid that is neither purely helical
nor purely icosahedral, and may possess
extra structures such as protein tails or a
complex outer walls

19.  The poxviruses are large, complex viruses that
have an unusual morphology. The viral genome
is associated with proteins within a central disk
structure known as a nucleoid. The nucleoid is
surrounded by a membrane and two lateral
bodies of unknown function. The virus has an
outer envelope with a thick layer of protein
studded over its surface. The whole virion is
slightly pleiomorphic, ranging from ovoid to
brick shape
/

21.  • Enveloped viruses
obtain their envelope by
budding through a host
cell membrane
 • In some cases, the
virus buds through the
plasma membrane but in
other cases the envelope
may be derived from
internal cell membranes
such as those of the
Golgi body or the
nucleus

22. Enveloped helical virus Enveloped icosahedral virus

23.  These spike may be involved in virus
attachment to host cell surface.
 Spike project about 10 nm from the surface
at 7 to 8 nm intervals.
 Most viral glycoproteins occur as membrane-
anchored peplomers (spikes) extending
outward from the envelope of enveloped
viruses