Dr. Ahmed Morad Asaad

sixcageyMechanics

Feb 22, 2014 (3 years and 5 months ago)

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NAJRAN UNIVERSITY

College of Medicine

Microbiology &Immunology Course

Lecture No. 18

By

Dr. Ahmed
Morad

Asaad

Associate Professor of Microbiology

Size:

3 methods are used to determine viruses size:

1
-

Filtration through filters of known pore sizes

2
-

Determination of sedimentation rate in ultracentrifuge

3
-

Using electron microscopy


The unit of measurement is nanometer


According to the sized, viruses may be:


Small viruses (20


30 nm) such as Polio and
Coxackie

viruses


Medium
-
sized viruses (75


150 nm) such as influenza and
measles viruses


Large viruses (200


300 nm) such as chicken pox virus

Shape of viruses:


Most viruses are spherical in shape


Brick
-
shaped virus such as poxviruses


Bullet
-
shaped virus such as
rhabdoviruses

(rabies virus)

Structure of viruses:

The viral particle (
virion
) consists of a nucleic acid core (virus
genome) surrounded by a protein coat (
capsid
). Some viruses are
enveloped.

1
-

Viral nucleic acid:


Viruses contain a single kind of nucleic acids either DNA or RNA
that encode the genetic information necessary for viral replication


The genome may be single
-
stranded or double
-
stranded

Functions of viral nucleic acids:


It is the essential infectious component of the
virion


It encodes the genetic information necessary for viral replication


It is the site of genetic material which carries the heritable
characteristics of the virus


The type of nucleic acid and
strandedness

are major characters
for classifying viruses

2
-

Capsid
:


It is the protein coat surrounding the viral genome


It is made of tiny protein subunits called
capsomeres


The nucleic acid + its protein coat =
nucleocapsid

Functions:


It protects the nucleic acid from damage in external environment


It facilitates the attachment of the virus to host cells in the
process of infection


It represents the viral antigen