Virus-General structure -Micro-content

1. Virus- General
Structure
Micro-content
Mrs.BiBi Hajira
M. Sc(Nursing)

2. •Edward Jenner (1798),
introduced the term virus in
microbiology.
•The concept of virus - Virus in
Greek means poison

3. Definition
A virus is a non-cellular particle
made up of genetic material and
protein that can invade living cells.

4. General characteristics of viruses
 Viruses are smaller than bacteria, they range in
size between 20-300 nanometer (nm)
 Viruses contain only one type of nucleic acid,
either DNA or RNA, but never both.
 Viruses consist of nucleic acid surrounded by a
protein coat. Some V-- have additional
lipoprotein envelope.

6. General conti….
 Viruses have of lack cellular organelles, such as
Mitochondria and Ribosomes.
 Viruses are obligate cellular parasites. They
replicate only inside living cells.
 Viruses replicate through replication of their
nucleic acid and synthesis of the viral protein.
 Viruses do not undergo binary fission. V-- do not
multiply in chemically defined media.

7. General structure of viruses
All viruses contain the following three components:
1) A nucleic acid genome
2) A protein capsid that covers the genome.
Together this is called the nucleocapsid
3] lipid envelope

8. A: Genomes
While the genomes of all known cells
are comprised of double stranded
DNA, the genomes of viruses can be
comprised of single or double
stranded DNA or RNA.

9. B: Protein Capsid
 Viral genomes are surrounded by protein shells
known as capsids. A capsid is almost always made up
of repeating structural subunits called capsomeres. The
capsid protects nucleic acid from inactivation by the
outer physical conditions.
 Structure of capsid give the symmetry to the virus.
Virus particle may be either cubicle or helical or binal
or complex symmetry.

11. C: Viral Envelope
 In some animal viruses, the nucleocapsid is
surrounded by a membrane, also called
an envelope.
 The envelope is a Bilayer of Lipoprotein And
Glycoprotein.
 These viral proteins serve many purposes, such as
binding to receptors on the host cell, (,proteins
hormones, neurotransmitters)

12. Symmetry of viruses
 Symmetry refers to the way in which capsomere units
are arranged in viral capsid.
 Two kinds of symmetry are recognized in the viruses
which corresponds to two primary shape ie. Rod and
spherical shape of virus.
 Rod shaped virus have helical symmetry and spherical
shaped virus have icosahedral symmetry.
Cubic symmetry:The virus particle is in shape (almost
spherical particle) and the nucleic acid contained inside
the capsid.
Helical symmetry: (rod shaped) The virus particle is
elongated or pleomorphic (not spherical), and the
nucleic acid is spiral.
complex symmetry: The virus particle does not confirm
either cubic or helical symmetry.