Viruses: Definition, Characteristics, Classification, Breeding and Role in Biology

Friends of the science portal this time we will continue with natural science material, especially Biology. If previously explained about biodiversity . This time, we will learn about viruses. Note the explanation below that will explain many things about the meaning, characteristics, classification, breeding and role of viruses in biology .

Viruses are part of microorganisms. Named part of microorganisms because it is a living creature whose size is only a few micro. Or maybe smaller than that, because 1 micron is equal to 0.001 mm.


Characteristics of Viruses

Then what are the characteristics possessed by the virus? Viruses have several characteristics. The characteristics of the virus are:

  1. Viruses have only one type of nucleic acid that is covered by a capsid or protein coat. These nucleic acids are DNA or RNA.
  2. Very small virus size. The size of the virus is between 25 – 300 nm. For 1 nm is 10-9 m)
  3. The body of this virus is not cell-shaped. So that this virus does not have a cell nucleus, plasma membrane, and cytoplasm.
  4. Viruses can only live and multiply in living cells or are known as obligate intracellular parasites.
  5. The virus is a creature of metaorganism. Metaorganism is a transitional form between inanimate objects or having crystallic properties and living or reproducing things.
  6. Viruses have several body shapes. The body shape of the virus is round, stem, T shape, and cylindrical.

Virus Body Structure

Thus the characteristics possessed by the virus. If the virus is not a cell. What is the body structure of the virus? In general, the body structure that is owned by a virus consists of nucleic acids and capsid. In addition, viruses also have an additional structure.

These nucleic acids consist of DNA or deoxyribo nucleid acid or RNA or ribonucleid acid. The explanation of the body structure possessed by the virus can be explained as follows.

Capsid . The capsid is a part of the structure of the body of the virus which is the covering layer for DNA or RNA in the virus. This capsid can be found on the head of the virus.

Kapsomer . The capsomer is part of the body structure of the virus which contains a small amount of protein and will combine to form a capsid.

Cell wrapping . Wrapping cells are part of the body structure of the virus that lines DNA or RNA. These wrapping cells contain lipoproteins or lipids and proteins which are plasma membranes and originate from virus host cells.

Sheath and tail fibers . The sheath and tail fibers are part of the body structure of the virus used by the virus to attach the body to the host cell.

Also read:  Definition, Function and Types of Enzymes

Virus Classification

After understanding about the body structure of the virus. Next, how about virus classification? The classification for types of viruses are based on certain things, which are as follows.

1. Based on the organism being attacked

Viruses can be classified into three, namely as follows.

First , bacteriophage is a virus that attacks bacterial cells. Examples of bacteriophages are viruses T6, T4, and T2.

Second , animal viruses are viruses that attack animal cells. This virus, such as Rhabdovirus which can cause rabies in dogs and monkeys, Rous Sarcoma Virus or RSV that can cause cancer in chickens, and Polloma which can cause tumors.

Third , plant viruses are viruses that attack plant cells. These plant viruses such as the tungro virus can cause disease in rice plants, Citrus Vein Phloem Degeneration or CVPD which can cause disease in oranges, and Tobacco Mozaic Virus or TMV which can cause mosaics or yellow spots on tobacco plants.

2. Based on the composition of nucleic acids

The grouping of viruses can be distinguished as follows.

First , viruses with single-stranded DNA or ssDNA, for example Parvoviruses which must infect along with Adenovirus in order to grow.

Second , viruses with double-stranded DNA or dsDNA, for example, Adenoviruses which can cause diseases of the respiratory tract.

Third , viruses with single band RNA or positive ssRNA, where ssRNA viruses act as mRNAs that messenger RNA gene codes. Examples of viruses with single band RNA or positive ssRNA are Picorna, a virus that can cause polio.

Fourth , single band RNA or ssRNA is negative, where in this virus ssRNA is an mRNA template. Examples of single band RNA are Rhabdovirus which can cause rabies.

Double band RNA or dsRNA, for example, Reovirus can cause diarrhea. In the naming there is the letter ss is an extension of single stranded or single chain. Meanwhile, ds stands for double stranded or double chains.

Previously, it was mentioned about bacteriophage. Bacteriofage is the simplest biological unit that can replicate itself or multiply itself more.

The body of this bacteriophage consists of the head, tail and tail fibers. This phage tail functions as an infectious device to the host cell. The process of infection from bacteriophage in bacterial cells is also used by viruses to multiply.

The above process can be divided into two types. Types of bacteriophageal infection processes in bacterial cells are lysogenic and lytic or virulent.

Propagation of Viruses

Furthermore, how is the propagation of the virus? Viruses to multiply, viruses must use their host cell infection. The process of virus reproduction consists of two types, namely lytic and lysogenic types. The explanation of each type is as follows.

Lytic cycle

Where in the lytic cycle, replication of the viral genome can cause death in host cells. Viruses that can only replicate through the lytic cycle or lysis are called virulent viruses. The lytic cycle is still divided again. Where the lytic phase is divided into five phases, namely the adsorption phase, the injection or penetration phase, the synthesis phase, the assembly phase, and the lysis phase. The explanation of each is as follows.

  1. Adsorption phase. This phase begins with the attachment of the tail end of the virus to the bacterial cell wall. Furthermore, lysozyme enzymes are released to perforate the cell walls of the host.
  2. Injection or penetration phase. This phase is when the DNA or RNA of the virus is inserted into the host cell. The virus remains in the tail and tail outside the cell and will be separated and not function when DNA injection has been carried out.
  3. Synthesis phase. This phase is the phase in which viral DNA containing lysozyme enzymes will destroy bacterial DNA. Next, replicate yourself, perform protein synthesis so that it forms parts of the capsid, including the head, tail and tail fibers.
  4. Assembly phase. The phase in which the initially separate virus capsid parts are then assembled into a viral capsid. This process causes the formation of new viruses.
  5. Lysis phase. The phase in which the destruction of the host cell or lysis and release of new viruses that will infect other host cells, and so on.

Lysogenic cycle

This lysogenic cycle is a cycle of viral genome replication without destroying the host cell. Thus, viruses integrate into bacterial or host cell chromosomes.

The initial phase through which the lysogenic cycle is the same as the lytic cycle. Where through the adsorption phase and injection phase. After going through this phase, then going through the following phases, namely the merging phase, the cleavage phase, the synthesis phase, the assembly phase, and the lysis phase. The explanation of each phase is as follows.

The merging phase is a phase of the joining of viral DNA with bacterial DNA. As a result, infected bacteria will have viral DNA. Then, the phase of division, where the viral DNA that joins the bacterial DNA becomes inactive or profage.

Under these conditions, if bacterial DNA replicates, the inactive viral DNA will also replicate. Synthesis phase, is the phase where the DNA of an active virus will destroy bacterial DNA. Then, separate yourself.

Furthermore, the DNA of the virus will synthesize the host cell protein as well as self-replicating. The assembly phase, the phase in which the capsid formed from the host cell protein is assembled into a viral capsid.

Then, the new virus DNA enters the capsid to form a new virus. Lysis phase, is the phase in which lysis occurs in cells after the formation of new viral bacteria. Viruses that have formed will then attack bacteria or other host cells.

The Role of Viruses in Human Life

What is the role of viruses in the life of living things? Viruses have beneficial and detrimental benefits for humans and animals. The benefits of viruses for humans are four.

  1. Viruses to make antitoxin substances.
  2. Viruses are used as anti-bacterial, for example in food product intruding bacteria that have been preserved.
  3. In making vaccines, such as smallpox vaccine, measles vaccine, and polio vaccine.
  4. Viruses for making insulin, such as cancer-causing viruses, can be transplanted into genes that produce insulin into bacteria cells. Thus, when bacterial cells replicate, they also produce insulin.

Although the virus has beneficial benefits for humans. However, there are also viruses that can harm humans. This harmful virus, in general, causes disease infection.

Viruses that can cause disease infections are classified into three groups. First, the virus that causes human disease. This virus includes influenza virus which can cause flu in humans.

Then, the Ebola Virus which can cause Ebola disease in humans. Avian influeza virus which can cause bird flu virus. Human Immunodeficiency or HIV which can cause AIDS.

Finally, Poliavirus is a virus that can cause polio. Besides causing diseases in humans, viruses can also cause diseases in animals and plants.

Viruses that can cause diseases in plants are the Tungro Virus which can cause rice to become stunted. Then, Tobacco Mozaic Virus or TMV is a virus that can cause mosaic spots on tobacco leaves.

In addition, Citrus Leprosis Virus or CLV is a virus that causes disease in citrus plants. Furthermore, viruses can cause diseases in animals. These viruses are New Castle Disease or NCD or tetelo virus.

Then, Adenovirus is a virus that can cause respiratory diseases in animals. Rhabdovirus is a virus that causes rabies in cats, monkeys and dogs.

Thus, the presentation of Definition, Characteristics, Classification, Breeding and the Role of Viruses in Biology. Hopefully this article can help friends of the science portal to understand about viruses. Have a good study.

by Abdullah Sam
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