Viruses are small obligate intracellular parasites that consist of either DNA or RNA surrounded by a protein coat. They can only reproduce inside host cells by utilizing the host's cellular machinery. Viruses come in different shapes and sizes but are all smaller than bacteria. They vary in their structure with some having an outer envelope, but their core components are always their genetic material and protein coating. Viruses infect cells and in order to replicate, their nucleic acids must enter the cell and commandeer its metabolic processes.

2. What are viruses?
– Small obligated intracellular parasites
– Virion
 Complete virus particle: nucleic acid + protein coat, which may be surrounded
by an envelope
 It is the form in which the virus moves between cells or hosts
– Viral Genome
 A Virus consists of either RNA or DNA genome surrounded by a protective virus-
coded protein coat called capsid
– Their propagation depends on specialized host cells which supply the machinery
for replication, metabolism and biosynthesis.

3. Viruses
 Viruses do not breathe
 Viruses do not metabolize
 Viruses do not grow
 However they do reproduce

4. Viral structure

5. Viral structure continued..
– Varies in size, shape and symmetry
– Viruses are smaller than bacteria
 The nucleic acid (DNA or RNA) could be single or double stranded
 The capsid or protein coat functions in protecting the genetic
material during viral infection
 Some viruses consist of an outer envelope which encloses the
coat and is made up of previously infected cells

7. Bacteriophage
– Bacteriophage
 Virus that infects prokaryotic (bacterial) cells.
– Nucleocapsid
 Consists of a viral nucleic acid and a protein coat
 Represents the packaged form of the viral genome

8. Structure of a bacteriophage

9. Viral Replication
– When a virus infects a cell, nucleic acid must be uncoated and gain
access to metabolic machinery of the cell

11. REFERENCES
 Dangol, R. (2013) Viruses. Available from SlideShare at
https://www.slideshare.net/mobile/rajendra930136/virus-23717258 (accessed, 30
August 2018)
 Muhammed, A. (2015) Organization and characteristics of Viruses. Available from
SlideShare at https://www.slideshare.net/mobile/asifkanth7861/general-organization-
and-characteristics-of-virus (accessed, 302 August 2018)
 Parungao, M. (2012) viral structure, classification & replication. Available from SlideShare
at https://www.slideshare.net/mobile/lhenparungao/virus-structure-classification-
replication (accessed, 30 August 2018)
 Rao, T. (2013) Viral structure and replication. Available from SlideShare at
https://www.slideshare.net/mobile/doctorrao/virus-structure-and-replication (accessed,
30 August 2018)
 Sun, K. (2012) Viruses. Available from SlideShare at
https://www.slideshare.net/mobile/kerorosun/viruses-11920700 (accessed, 30 August
2018)