FEDERAL UNIVERSITY OF AGRICULTURE

COLLEGE OF BIOSCIENCES

DEPARTMENT OF MICROBIOLOGY LECTURER:

PROF. AKINTOKUN
 VIROLOGY

Virology is the study of viruses

What are viruses - viruses are small filterable and obligate intracellular parasite requiring a lung host for it's multiplication outside a
living cell ey cannot survive ble ey need the metabolism and structures or the host cells to support formation of new viruses.

When a virus insect a host cell it takes over the cellular activities of the host cell.

Viruses are not living blc ey are not made up of cells. That is ey have no degree of organisation - cell tissues and organs, ey cannot
exchange material within their surrounding and ey cannot transform energy and do not ability to grow to make their own energy but ey
can replicate and adapt to eir enut.

EFFECTS OF VIRUSES ON HOST

Can cause lysis and death of host

Can cause alterations of cell surface

Can cause membrane apoptosis ie

cell death

Can cause changes in antigeniaity

and response of the host to presence
of virus leading to viral disease.
REASONS FOR STUDYING VIRUSES

They are important agents of human, animal and plant diseases.

Natural or mordiheel viruses can be used to target and kill center cells

Can be used to treat varieties of genetic disease as gene therapy.

Some can serve as vaccine

Some have the potentials to develop into useful biological with therapeutic benefits to humans Biologies are biological agents eg
medicines, vaccines, growth factors, immune modulators, monoclonal bag, products derived from human bid and plasma.

APPLICATIONS

1. Phase typing of bacteria - some vs are classified into strains based on the spectrum of phases, identification of phases can
provide useful epidemiological information during outbreaks of disease cause by bacteria.

2. Sources of enzymes - A number of enzymes used in molecular biology are virus enzymes e.g RNA polymerases from phages,
reverse transcriptase from retroviruses.

3. Pesticides - some insects pests can be controlled by viruses eg family Baculovindae.

4. Antibacterial agents - some phages are used to treat bacteria infections of man

5. Anticancer agents - genetically modified strans of viruses eg Herpes simpler virus and vaccin is viruses are able to infect and
destroy specific tumor cells but unable to infect normal cells.

6. Gene vectors for protein pdn - viruses of Adenoviruses are used as vectors to take genes into animal cells growing in cultures.
This technique can be used

To insert into genes encoding useful protein e.g vaccine and cell can be used for mass pdn or proteins.

7.Gene vectors for brt or genetic diseases- under is severe immunodeficiency have been treated to retroviruses as vectors to
introduce their stem cells. Stem cells are cells to the potentials to develop into many different types of cells in the body. They serve
as a repair system for the body.
 HISTORY OF VIRUSES

The 1st evidence of existence of viruse came from expls to filters that had pores small enough to retain bacteria. 1892
Dmitri/vanowsky used one of there filters to show that sap of disease tobacco plt remained infections to healthy tobacco dlts despite
having been filtered. He concluded that infections agents is filtered and cancelled it poisonous fluid marhnus Beijerinck 1898 called
the filtered infections substance a virus and this discovery is considered to be the beginning of virology. He also discovered that the
filtered infections substance could pass through porcelain filter and diffuse them agar that retain bacteria but cannot be Cultured
except on lung growing plants and named the substance as tobacco mosaic virus (TMV).

1935, Stanley crystallized the virus causing mosaic in tobacco plant. He found that the crystallized substance was infectious when
inoculated into healthy tobacco plants. He concluded that the virus

was not a typical cell of lung organisms.

Bawden and plore 1938 analysed the crystallized virus and found that they contain RNA and protein.

Fraenkel- conrat 1950 confirmed the genetic material of TMV as RNA.

1916, Frederick Tower and Felix d'Herelle reported the cultures of bacteria cells were lysed by some agents. The agents were able to
cause lysis of bacteria cells even after it has passed through filter bacteria filter. But when the agents were heated after passing through
bacteria filter, they were lysed suggesting that the agents were destroyed after heating.

Herelle in 1917 named the agent as bacteria phage (bacteria eater) blc. It can cause lysis of bacteria cells.

Other dert include discovery of mycoviruses in cultivated mushroom by Hollings 1962 cyanophages-viruses infecting blue green algae
in 1963 by safferman and Morris .
Viroid by Diener and Raymer 1967, prior by prisoner and Hiv by Luc Montagnier 1983 viroid.

Viroids are infectious entities smaller than viruse, exist in nature.they are caused directly disease and not normal disease eg or viroid is
potato spindle tuber viroid (PST V) can caused potatoes disease they differ in properties from viruses in different features

1. Pathogen exists in viroid as encapsulated in the RNA

2. viron are not detected in infected tissues

3. Infectious RNA is of low molecular weight

4. Infectious RNA replicates autonomously in susceptible cells

5.Infectious RNA consults of one molecular species only they consists of single molecule of curanler snay RNA conra protein cont
or envelop and do not code for protein. Viroids replicate but but mechanism.

Prions - are proteinaceous infectious agents found in animals and humans. They contain no detectable NA ie lack DNA or RNA.
Electron microscopy reveals filements rather dn viruse particles. They are remarkably resistant to formaldehyde and nucleases, more
resistant to inactivation by height, heat and acid dn viruses they are inactivated by hypochlorite, NaoH, autoclave prions cause disease
slowly e.g creeitzfeildt-jacob disease in humans and scapie in sheep

EVOLUTION OF VIRUS

Evolution of viruses are not known because when exploring evolutionary history of most organizations scientists looks at tonsil
records and similar historic records. However, viruses do not have tonsil records. Researchers can only hypothesize about viruses by
evolutionary history investigating into how today's viruses evolve and by using biochemical and genetic information to create
speculative virus hytrones. However, 3 hypothesis were accepted.

1. Devolution or regressive hypothesis - the regressive hypothesis proposes to explain the origin of viruses by suggesting what is
evolved from free living cells. However, many components of how this process occurred is a mystery.
 2.Escapist or progressive hypothesis. The hypothesis accounts for virus having either RNA or DNA genome suggesting that virus
originated from RNA and DNA mols that escaped from a host cell. But disease hypothesis does not explain the stress of virus particles
and the Capsids

3.Self replication hypothesis state that virus exists as a system of self replication similar to that of other self replicating mols ,
likely evolving along side the cells or the hosts. Studies of some plt pathogens support this hypothesis .

STRUCTURE

Virus consists of NA core surrounded by a protein coat or capsid.

NA core of virus consists of DNA or RNA which could be either single stranded or double stranded molecules. The NA may be in
linear or circular form and have plus or minor polarity.

Capsids also called protein coat surround dNA Capsids are made up of slyworks called capsomers. Each capsomer consists of one or
several proteins. Arrangements of capsomers gives the virus structure it's geometric symmetry. There are 3 forms of symmetry.

1. Helical or cylindrical viruses - there are 2 types naked Capsid e.g TMV, Bacteriophages miz enveloped capsid e.g influenza virus

2.Polyhedral or icosahedron viruses - 2 types Naked Capsid e.g Adenovirus, poino

virus Enveloped Capsid e.g Herpes Simplex virus

3. Complex viruses - 2 types

Capsids not clearly identified e.g vaccinis virus identified but have some other structural attached e.g T even Bacteriophages, vaccinis
virus

Envelop - viruses are surrounded by the membraneous envelop. Envelope is art 10-15Am
thick. The envelop is made up of proteins, lipids and CHos can combined to form glycoproteins and lipoprotein. Protein component of
envelop is of viral origin, lipids and CHO may be of host membrane viral proteins.

Spikes - spikes are attached to the outer surface of the envelope and is made up of glycoproteins.

Spikes have agglutination proteins.

Viral proteins - protein found in viruses are grouped into 4

Envelop protein - virus possessing envelope have their envelop trade up or protein.

Nucleocapsid protein - viral capsids are made up of protein. The enelical capsids contain single type of protein while the icosahedron
capsid contain several types of proteins.

Core proteins - protein found in the NA

Viral enzyme - some enzymes e.g RNA and reverse transcriptase, protein lanase and DNA dependent RNA polymerases enzymes
contain protein.

CHO - CHo is found in host cell or viral genre of envelope. CHO are hexoses and hexamenes present in the form of glycoproteins and
lipids
Reproduction but spontaneously assemble within cells. Viruses self assembly within host cells has implications for the study of the
origin of life,as it lends credence to the hypothesis that life could have started as self assembling organic molecules.

Characteristics of viruses

1. Presence of single nucleotide which is either DNA or RNA. The DNA or RNA could be single stranded or double stranded

2. They are covered with protective coat of protein called capsid

3. They do not have organized cell structures no nucleus

4. They are potentially infectious

5. They cannot grow on genetic material only and reproduction is from the genetic material only

6. Absence of ribosomes

7. Absence of enzymes for energy metabolism

8. Absence of information for the production of enzymes in the energy cycle

9. Absence of information for the synthesis of ribosomes, proteinsm ribosomal RNA and soluble tRNA

Occurrence

Viruses occur in a wide range of hosts e.g

 Plants: angiosperms, gymnosperms, ferns, algae and fungi

 Animals : protozoan, insects, fish, amphibians, birds, mammals, humans

Morphology

Shape: viruses have different shapes e.g

 Spheroid or cuboid: Adenoviruses

 Elongated: potato viruses

 Flexuous or coiled:beef yellow

 Bullet: Rabies virus

 Filamentous bacteriophage: Liz

 Pleomorphic : alfalfa mosaic

Size: they have variable sizes: their sizes are determined by

 Ultracentrifugation and electron microscope varying from 20nm to 300nm in diameter. They are smaller and batter, although
some vision are larger and best e.g lymphogranuloma (300-400nm) in size.

 They are smaller than bacteria, although some viruses are larger than bacteria e.g lymphogranmuloma (300-400um) in size

Structure

A coat virus consists of a nuclei acid core, surrounded by a protein coat or capsid. A complete set of viruses is known as nucleocapsid .
A nucleocapsid could be naked or enveloped by a loose covering. The capsid is composed of a larger number of subunits known as
capsomers. Chemically, the envelope of a virus is made up of proteins and glycoproteins. Due to the presence of lipid, the envelope
seems flexible and loose . Envelope is composed of both the host and viral components I.e protein (viral specific) and carbohydrates
(host specific). Spikes are projections of glycoproteins on the outer surface of the envelope which are arranged into distinct units.
Spikes have agglutination proteins. Morphological types of viruses have been categorized into three groups.

1. Helical (cylindrical) viruses: (a)naked capsid e.g TMV , Bacteriophage miz

(b) Envelope capsid e.g influenza virus

2. Polyhedral (icosahedral) viruses (a) Naked capsid e.g adenoviruses, polio virus

(b) Enveloped capsid e.g Herpes Simplex virus

3. Complex viruses: Capsids not clearly identified e.g Vaccinia virus

4. Capsids to which some other structures are attached e.g Bacteriophages

1. Helical viruses

Helical viruses are elongated, rod shaped, rigid or flexible. Thier capsid is hollow cylinder with a helical structure. Capsid consists of
monomers arranged helically on a rotational axis. The helical Capsids may be naked e.g TMV or enveloped e.g influenza virus

Naked viruses

TMV is an examples of naked viruses. It is rod shaped, ssRNA helix of coiled RNA. Protein wat of the virus contains a number of
identical subunits (monomers) which are arranged in helical manner. Capsids consist of several capsomers. Each composed of few
monomers Genetic material ssRNA has a molecular weight of 2.06 x 10⁶ Dalton. The capsid protects the RNA molecule.
Enveloped Viruses

When the helical viruses are enclosed within an envelope, they are known as enveloped helical viruses e.g influenza virus. Enveloped
is composed of viral proteins and host cell components i.e lipids and