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1. Introduction to
Virology
Student Name: Noor Almozainy
Supervision of Dr: Anas Dablool

2. 01 Define virus
llustrate the structure of
virus and explain
function of each
structural component
02
Explain general
properties of viruses
03
Compare helical and
cubic viral
symmetries
04
Objectives
05 Explain general steps of
viral replication cycle

3. virus
is an infectious agent that has a simple
acellular structure, that is too small
to be seen by light microscopy.

4. General Properties of
Viruses
1. Viruses are very small
•They are seen only by the
electron microscope.
2. Viruses have a Minimal acellular
structure
• Viruses are minimally constructed of
two components;
• a protein coat that surrounds
• the nucleic acid genome .

5. General Properties of Viruses
3. Viruses contain a single type of Nucleic acid
4. They are obligatory intracellular parasites
• Viruses can only replicate in living cells.
•All viruses have no metabolic activity outside the host
cell.
• Viruses exist as inactive macromolecules outside of the
host cell.

6. 6. Viruses have Special replication cycle
•Reproduction of viruses occurs by assembly of the
individual components rather than by binary fission like
bacteria.
7. Viruses can infect all types of cells
General Properties
of Viruses

7. Virus Structure
Principles of virus structure
A complete infective virus particle
(virion) consists of three parts:
1. Nucleic acid
2. Capsid
3. Envelope

8. 1. Nucleic acid
• It is either DNA or RNA but never both.
•It may be single-stranded or double-
stranded

9. Functions of nucleic acid:
• It codes for the production of viral proteins.
• It is the infectious part of the virus;
empty virus particles are none-infectious.

10. 2. Capsid
Capsid
● It is a protein coat surrounding the nucleic
acid.
● It is composed of protein structural units
called capsomeres.
Functions of Capsid
• Protection of nucleic acid core.
• It possesses receptor binding sites that enable the
virus to attach to a specific receptor site on the
host cell.

11. Capsid Symmetry
Helical Symmetry
The structural units of the virus
are assembled in either of two
geometric configurations
(symmetries) :
● Helical Symmetry.
● Cubic symmetry.
Cubic symmetry
Cubic symmetry :
Structural units are
assembled together to
form an icosahedron.
Helical Symmetry:
Consist of repeated
units into a helical
cylinder.

12. 3. Envelope
Some viruses are surrounded by a lipid envelope.
•Envelope contain viral
glycoproteins exposed on
its surface.

13. Virus Replication Cycle
1-Attachment
A virus attaches to a specific receptor site on
the host cell membrane through attachment
proteins in the capsid or via glycoproteins
embedded in the viral envelope. The
specificity of this interaction determines the
host (and the cells within the host) that can be
infected by a particular virus.
2-Penetration
is the passage of the virion from the
surface of the cell, across the cell
membrane and into the cytoplasm.
3-Uncoating
is the physical separation of
the viral nucleic acid from the
outer structural components
of the virion.

14. Synthesis of new
viral components
•Gene expression of viral genes
(transcription and translation of
viral genes) to produce viral
proteins.
• Replication of viral genome.
Assembly
is the association of
the new virus genomes
and viral structural
proteins to form new
virus particles.
• Some viruses may escape
from the host cell by causing
cell lysis (rupture).
• Enveloped viruses typically "
bud" from the host cell.
During budding, enveloped
viruses acquire their
envelope.
Release
Virus Replication Cycle

15. https://youtu.be/OU4mIj_6OlE
video

16. The reviewer
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwj8-
5GKwZr2AhXP4IUKHZnSCOoQFnoECDIQAw&url=https%3A%2F%2Fbio.libretexts.org%2FBookshelves%2FI
ntroductory_and_General_Biology%2FBook%253A_General_Biology_(Boundless)%2F21%253A_Viruses%2F
21.2%253A_Virus_Infections_and_Hosts%2F21.2A%253A_Steps_of_Virus_Infections&usg=AOvVaw0b0xya5t
y6CR7TIYf5r7TY
https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwimmeSnt5r2AhVJSx
oKHa8uBYcQFnoECBEQAw&url=https%3A%2F%2Fwww.atsu.edu%2Ffaculty%2Fchamberlain%2Fwebsite%
2Ftritzmed%2FLECTS%2FPROPERT.HTM&usg=AOvVaw2SUHhteRMBC7pdjpZUMncf

17. Thanks!