GENERAL PROPERTIES OF VIRUS

• Virus are the smallest unicellular organism that are obligate intracellular.

• Virus are too small to be seen with a light microscope.

• Virus are microscopic infectious agents that can infect living organisms, including humans, animals, plants, and even microorganisms.

• Viruses lack the ability to carry out essential life processes on their own.

• Viruses can cause a wide range of diseases in their hosts, ranging from mild illnesses such as the common cold to severe conditions such as influenza, COVID-19.

• Multiply through complex method not by binary fission.

CHARACTERISTICS OF VIRUS

# Characteristics of viruses are:

• They are obligate intracellular.

• Contain DNA or RNA, never both.

• Filterable – through bacteria filter.

• Virus cannot grow in artificial media.

• Multiply by complex method not by binary fission.

• Viruses do not have proper cellular organization.

• Do not have cell wall, cell membrane or cellular organelles including ribosomes.

• They do not susceptible to antibacterial antibiotics.

PROPERTIES OF VIRUS

# MORPHOLOGY OF VIRUS:

1. SIZE

• Virus are much smaller than other cellular organism.

• The size of virus ranges from (20-300) nm in diameter.

a) Smallest virus – parvovirus (20nm)

b) Largest virus - poxvirus (300nm)

• Size of virus can be determine by:

a) Electron microscopy

b) Ultracentrifugation

2. SHAPE

• The overall shape of virus varies in different groups.

a) Rabies virus : Bullet shape

b) Poxvirus : Brick shaped

c) Adenovirus : Space vehicle shaped

• Some virus are irregular and pleomorphic in shape.

3. SYMMETRY

• Three type of symmetry are determine in virus.

a) Icosahedral symmetry : All DNA viruses (except-poxvirus) & most of the RNA virus have icosahedral symmetry. Example – papova, picorna, adenovirus & herpes, etc.

b) Helical symmetry : most of the helical virus are enveloped & all are RNA virus. Examples – myxoviruses, rhaboviruses, filovirus, etc.

c) Complex symmetry : virus which do not have either above symmetry. Such as POXVIRUS.

4. STRUCTURE

• They consist of the following components :

a) Genetic Material: Viruses contain genetic material, either DNA or RNA.

• The genetic material can be single-stranded or double-stranded

• Linear or circular, depending on the virus type

b) Capsid: The genetic material of a virus is enclosed within a protein coat called the capsid.

• The capsid provides protection and stability to the genetic material.

• It is composed of repeating protein subunits called capsomeres.

• The arrangement of capsomeres determines the shape of the capsid, which can be helical, icosahedral, or complex.

c) Envelope (if present): Some viruses have an additional outer envelope surrounding the capsid.

• The envelope is a lipid bilayer derived from the host cell membrane.

• Embedded in the envelope are viral proteins, including glycoproteins, which play a crucial role in host cell recognition and entry.

d) Spike Proteins: Many enveloped viruses have spike-like projections called spike proteins or peplomers that protrude from the envelope.

• These spike proteins are involved in attaching to specific receptors on host cells and facilitating viral entry.

e) Matrix Proteins (if present): Some viruses have matrix proteins located between the capsid and the envelope.

• These proteins help maintain the structural integrity of the virus particle and assist in viral assembly and release.

# CHEMICAL PROPERTIES

• Viruses possess several chemical properties that contribute to their structure and function.

• Some chemical properties of viruses are :

1. Nucleic Acid Composition: Viruses can have either DNA or RNA as their genetic material. The nucleic acid can be single-stranded or double-stranded, and its sequence carries the genetic information necessary for viral replication and protein synthesis.

2. Protein Composition: The capsid of a virus is primarily composed of proteins. The composition and arrangement of these proteins can vary among different viruses

3. Lipid Composition (Enveloped Viruses): Some viruses have an outer envelope derived from the host cell membrane. The envelope is composed of lipids, primarily phospholipids, similar to the host cell membrane.

4. Glycoproteins: Many viruses have viral proteins on their surface, including spike proteins or peplomers. The glycoproteins play a crucial role in viral attachment to host cells and can also serve as targets for the immune system.

5. Enzymes: Some viruses carry specific enzymes within their structure that are required for various stages of their replication cycle.

6. Genetic Variation: Viruses have the ability to undergo genetic mutations and genetic recombination, leading to genetic variation within a viral population.

7. Stability: The stability of viruses can vary depending on their chemical properties. Factors such as temperature, pH, humidity, and exposure to environmental conditions can affect the stability of viral particles.

REPLICATION OF VIRUS

• Virus do not undergo binary fission (seen in bacteria), but undergo a complex method of cell division.

• LINK - https://docnotemaster.in/virus-replication

SUSCEPTIBILITY TO PHYSICAL & CHEMICAL PROPERTIES

• some aspects of virus susceptibility to chemical and physical properties:

1. Temperature:

• Most viruses are heat labile.

2. pH:

• The pH level of the environment can impact the stability and infectivity of viruses.

• Each virus has an optimal pH range at which it remains stable and infectious.

• Deviations from this range can affect the virus's ability to survive and infect host cells.

3. Chemical Disinfectants:

• Viruses can exhibit different levels of susceptibility to various chemical disinfectants.

• Some viruses are more resistant and require stronger disinfectants or longer exposure times to be effectively inactivated.

• Common disinfectants include alcohol-based solutions, chlorine-based compounds, and hydrogen peroxide.

4. Ultraviolet (UV) Light:

• UV light can be used to inactivate viruses by damaging their genetic material.

5. Desiccation: The ability of viruses to survive on dry surfaces, known as desiccation.

6. Osmolarity:

• Changes in osmolarity, the concentration of solutes in a solution, can affect virus stability.

• Viruses can be sensitive to changes in osmotic pressure, and significant deviations from their optimal osmolarity range can lead to loss of infectivity.

7. Antibiotics :

• virus are resistant to antibiotics.