Table of Contents
The Protein Capsid
A protein capsid is a protein shell that surrounds the genetic material of some viruses. Capsids are made up of proteins that form a shell around the virus’ genetic material. The proteins that make up the capsid can be different depending on the virus. Some viruses have a capsid that is made up of a single type of protein, while others have a capsid that is made up of multiple types of proteins.
The protein capsid is important for a few reasons. First, the capsid protects the virus’ genetic material from the outside environment. Second, the capsid helps the virus to enter and infect cells. Third, the capsid can help the virus to spread from one cell to another. Finally, the capsid can help the virus to evade the immune system.
The protein capsid is also important for vaccine development. A vaccine is a substance that is used to help the body to build immunity to a virus. The protein capsid can be used in vaccines to help the body to build immunity to the virus. This is important because it can help to prevent infections with the virus.
Classification of Viruses Based on Morphology
There are five main classes of viruses based on morphology, which are determined by the shape of their particles. The five classes are:
1. helical viruses
2. icosahedral viruses
3. filamentous viruses
4. pleomorphic viruses
5. viral complexes
Helical viruses are shaped like a helix or a coil. The most well-known example of a helical virus is the common cold virus, which is also known as the rhinovirus. Icosahedral viruses are shaped like a regular polyhedron with 20 triangular faces. The most well-known example of an icosahedral virus is the human immunodeficiency virus, or HIV.
Filamentous viruses are shaped like long, thin strands or rods. The most well-known example of a filamentous virus is the rabies virus. Pleomorphic viruses are viruses that have a variety of different shapes. The most well-known example of a pleomorphic virus is the Ebola virus.
Viral complexes are viruses that are made up of more than one particle. The most well-known example of a viral complex is the flu virus, which is made up of three different particles.
Classification of Viruses Based on the Presence of Nucleic Acid
There are three general types of viruses, each classified based on the presence or absence of nucleic acid. DNA viruses, RNA viruses, and retroviruses are each further subdivided based on the presence or absence of a capsid.
DNA viruses are composed of DNA and include adenoviruses, herpesviruses, papovaviruses, and poxviruses. These viruses are generally larger and more complex than other virus types. They contain a capsid, which is made of protein, and a nucleic acid core. The capsid surrounds and protects the nucleic acid.
RNA viruses are composed of RNA and include picornaviruses, reoviruses, and togaviruses. These viruses are generally smaller and less complex than other virus types. They contain a capsid, which is made of protein, and a nucleic acid core. The capsid surrounds and protects the nucleic acid.
Retroviruses are composed of RNA and include human immunodeficiency virus (HIV), human T-lymphotropic virus (HTLV), and simian immunodeficiency virus (SIV). Retroviruses are unique in that they contain an enzyme called reverse transcriptase. This enzyme converts the RNA of the virus into DNA. The DNA is then integrated into the host cell’s DNA. Retroviruses are thus able to replicate inside the host cell.
Classification of Viruses Based on the Host Range
Viruses are classified by their host range. This is the range of hosts that a virus can infect.
There are three classifications of viruses based on their host range:
1. Narrow-host range viruses
2. Broad-host range viruses
3. Omnivorous viruses
1. Narrow-host range viruses are viruses that can only infect a limited range of hosts.
2. Broad-host range viruses are viruses that can infect a wide range of hosts.
3. Omnivorous viruses are viruses that can infect both plants and animals.
Properties of Virus
Viruses are small, obligate intracellular parasites that lack the ability to replicate autonomously. They are highly diverse in terms of their genome, morphology, and host range.
Viruses are generally non-cellular, consisting of a nucleic acid genome (either DNA or RNA) encapsulated within a protein coat. The coat is sometimes surrounded by a lipid bilayer.
Viruses are obligate intracellular parasites that lack the ability to replicate autonomously. They must infect a host cell in order to replicate.
Viruses have a wide variety of genome sizes and shapes.
Viruses have a very wide host range, and can infect all types of cells.
Viruses are generally very sensitive to heat and UV radiation, and can be killed by exposure to these agents.
Classification of Viruses
There are three main types of viruses: DNA viruses, RNA viruses, and retroviruses.
DNA viruses are made of DNA and include herpesviruses, adenoviruses, and papovaviruses.
RNA viruses are made of RNA and include influenza viruses, HIV, and rabies virus.
Retroviruses are made of RNA and use an enzyme called reverse transcriptase to convert their RNA into DNA, which can then be integrated into the host cell’s DNA. Retroviruses include HIV and the human T-cell lymphotropic virus (HTLV).
Structure of Virus
The virus particle is a small, simple, and elegant piece of machinery. It is a self-replicating entity made up of a genome (DNA or RNA) enclosed in a protective protein coat. The genome contains the instructions for making new virus particles.
The coat is made of proteins that are specifically tailored to bind to the surface of a host cell. When the virus particle comes into contact with a host cell, it attaches to the cell surface and injects its genome into the cell.
The genome takes over the host cell’s machinery and uses it to make new virus particles. The infected cell lyses (ruptures) and releases the new virus particles, which can then go on to infect other cells.
2. Icosahedral Symmetry
Icosahedral symmetry is a type of symmetry found in three-dimensional objects. It is exhibited by objects with 20 faces (or edges). These faces can be arranged in any of the 120 possible ways, allowing the object to have fivefold rotational symmetry.
3. Virus Core Structure
A virus has a core structure that is made up of nucleic acid. This nucleic acid is either DNA or RNA. The core is surrounded by a protein coat. This coat helps to protect the virus and also helps it to attach to the host cell. The virus also has a glycoprotein shell. This shell helps the virus to enter the host cell.
1. DNA
is a molecule that encodes the genetic instructions used in the development and functioning of all living organisms.
2. DNA is composed of two strands of nucleotides twisted around each other to form a helix.
3. The sequence of nucleotides in DNA determines the genetic information of an organism.
4. DNA is replicated when cells divide so that each new cell has an exact copy of the DNA of the original cell.
5. DNA can be modified by enzymes called DNA polymerases.
6. DNA can be used to determine the relationships between organisms.
2. RNA
RNA editing is a process that alters the nucleotide sequence of pre-mRNA. This can change the amino acid sequence of the protein that the mRNA encodes. RNA editing is a type of post-transcriptional modification.
There are two types of RNA editing:
1. Site-specific RNA editing
2. Non-site-specific RNA editing
Site-specific RNA editing is the most common type of RNA editing. This type of RNA editing occurs at specific sites in the pre-mRNA. Non-site-specific RNA editing is less common than site-specific RNA editing. This type of RNA editing occurs at random sites in the pre-mRNA.
RNA editing is carried out by a variety of enzymes, including:
1. ADARs (adenosine deaminases that act on RNA)
2. APOBECs (apolipoprotein B mRNA editing enzymes)
3. C2H2 zinc fingers
RNA editing can change the protein sequence, and therefore the function, of a protein. For example, RNA editing can change a protein from an enzyme to a receptor.
Classification of Viruses Based on the Replication Properties and Site of Replication
Viruses are classified based on their replication properties and site of replication.
There are two types of viruses- DNA viruses and RNA viruses.
DNA viruses replicate in the nucleus of the host cell, while RNA viruses replicate in the cytoplasm of the host cell.
There are three types of DNA viruses- herpesviruses, adenoviruses, and papillomaviruses.
Herpesviruses replicate in the nucleus of the host cell, and their DNA is integrated into the host cell’s DNA.
Adenoviruses replicate in the nucleus of the host cell, and their DNA is not integrated into the host cell’s DNA.
Papillomaviruses replicate in the nucleus of the host cell, and their DNA is not integrated into the host cell’s DNA.
There are three types of RNA viruses- picornaviruses, flaviviruses, and togaviruses.
Picornaviruses replicate in the cytoplasm of the host cell, and their RNA is not integrated into the host cell’s DNA.
Flaviviruses replicate in the cytoplasm of the host cell, and their RNA is integrated into the host cell’s DNA.
Togaviruses replicate in the cytoplasm of the host cell, and their RNA is not integrated into the host cell’s DNA.
Animal Viruses
A virus is a small, nonliving particle that can only reproduce inside a living cell. Viruses are typically made up of genetic material (either DNA or RNA) and a protein coat.
There are many different types of viruses, and they can infect a variety of different cells in the body. Some viruses can cause serious diseases, such as AIDS, polio, and the flu.
Viruses are not alive and cannot reproduce on their own. To reproduce, a virus must invade a living cell and hijack its cellular machinery to produce new virus particles.
Some viruses, such as the flu, can spread from person to person. Other viruses, such as HIV, can be spread through contact with infected blood or other body fluids.
There is no cure for most viral infections, and they can only be treated symptomatically. Prevention is the best way to combat viral infections, through vaccination and good hygiene practices.
Plant Viruses
There are many types of plant viruses, but the most common are those that cause mosaic diseases. These viruses cause the leaves of infected plants to develop a mottled, patchy appearance. The virus particles are small and round, and they can be seen in the plant sap under a microscope.
Some plant viruses can also cause wilting or stunting of the plant. There is no cure for a virus infection, and the best way to control it is to destroy the infected plants.
Virus Infecting Insects
Baculoviruses are viruses that infect insects. They are classified as DNA viruses and have a double-stranded DNA genome. Baculoviruses are among the largest viruses known, and can be up to 500 nanometers in diameter.
There are several different types of baculoviruses, which infect different types of insects. Some of the most common types of baculoviruses include the baculovirus of the silkworm, the baculovirus of the rice weevil, and the baculovirus of the tobacco budworm.
Baculoviruses are highly pathogenic, and can cause significant damage to their insect hosts. They are also highly infectious, and can spread rapidly through insect populations.
Baculoviruses have been used as bioweapons, and can be deadly to insects. They have also been used as insecticides, and can be used to control insect populations.
Classification of Viruses Based on the Mode of Transmission
There are six main modes of viral transmission:
1. Contact transmission: This occurs when the virus is transmitted through direct contact with an infected person or object. Common examples of contact transmission include kissing, sharing food or drinks, and touching infected skin.
2. Airborne transmission: This occurs when the virus becomes airborne and is inhaled by a person. Common examples of airborne transmission include coughing and sneezing.
3. Vector-borne transmission: This occurs when the virus is transmitted through the bite of an infected vector. Common examples of vector-borne transmission include mosquitoes, ticks, and fleas.
4. Sexual transmission: This occurs when the virus is transmitted through sexual contact. Common examples of sexual transmission include vaginal, anal, and oral sex.
5. Mother-to-child transmission: This occurs when the virus is transmitted from the mother to her child during pregnancy, birth, or breastfeeding.
6. Fecal-oral transmission: This occurs when the virus is transmitted through contact with contaminated feces. Common examples of fecal-oral transmission include eating contaminated food and water, and contact with infected animals.
