Virus Structure, Types, Microbiology & Replication Of Virus

Virus:  

Viruses are microscopic parasites without a host cell, the virus cannot carry out its life-sustaining function or reproduce virus is much smaller than bacteria, the name of the virus from the Latin word meaning "poison".   

                                    

Size of virus:  

Viruses vary in diameter from 20 manometers(nm; 0,0000008 Inch) to 250 -400 nm; in diameter, the largest viruses measure about 500 nm and are about 700- 1,000 nm in length.

     

Types of viruses:  

• Flu
• Smallpox
• Rabies
• Measles
• Coronavirus
• Chickenpox
• Hepatitis 
• HIV
• Poliovirus

 

Microbiology:   

Virus do not have their metabolism and require a host cell to make a new product, therefor cannot naturally reproduce outside of the host cell. 

Structure of virus:   

Viruses contain nucleic acid, either DNA or RNA (but not both), and a protein coat, which encases the nucleic acid. Some viruses are also enclosed by an envelope of fat and protein molecules. In its infective form, outside the cell, a virus particle is called a virion. Each virion contains at least one unique protein synthesized by specific genes in its nucleic acid. Viroids (meaning "virus-like") are disease-causing organisms that contain only nucleic acid and have no structural proteins. Other virus-like particles called prions are composed primarily of a protein tightly integrated with a small nucleic acid molecule.

Replication of virus:

viruses are obligate intracellular pathogens that cannot replicate without the machinery and metabolism of the host cell. Although the replication life cycle of viruses differs greatly between species and categories of the virus, there is a generated pattern that can be described.

Attachment: 

The attachment itself is highly specific, between molecules on the outside, of the virus and receptors on the host cell surface. Viral proteins on the capsid or phospholipid envelope interact with specific receptors on the host cellular surface. This specificity determines the host range(tropism) of a virus.

Penetration:

Many un enveloped virus (or naked)virus injects their nucleic acid into the host cell, leaving an empty capsid on the outside, this process is termed penetration and is common with bacteriophage.

Uncoating:

The viral capsid is removed and degraded by viral coenzyme or host enzymes releasing the viral genomic nucleic acid.

Replication:

After the in genome has been uncoated, transcription or translation of the viral genome is initiated. It is this stage of viral replication that differs greatly between DNA and RNA viruses and viruses with opposite nucleic acid polarity. This process culminates in the de novo synthesis of the viral protein and genome.

Assembly: 

The complexity of viral assembly depends upon the virus being made, the simplest virus has a capsid composed of 3 different types of protein, Which assembles with little difficulty.

Release:

There are two methods of viral release lysis or budding. Lysis results in the death of an infected host cell, this type of virus is referred to as cytolytic. An example example is variola major also known as smallpox. Enveloped viruses, such as influenza A virus, are typically released from the host cell by budding. It is this process that results in the acquisition of the viral phospholipid envelope These types of viruses do not usually kill the infected cell and are termed cytopathic viruses.