Viruses: Meaning, Features, and Components

The virus is derived from Latin means Poisonous Fluid or Venom. The scientist who first coined the term virus was Pasture and the invention of the Virus was performed by Iwanosky. The virus which he determined was TMV (tobacco mosaic viruses).TMV is later crystallized by Stanley. Viruses are very small in size varying from 20-350nm. The smallest viruses regarded are extero-viruses which are less than 30nm in diameter.

Viruses with non-living properties

1. They are devoid of protoplasm

 2. They cant grow

3. They can be crystallized

Characteristics of viruses that are similar to those of live creatures 

1. They are made up of bio-chemical compounds

2. They contain DNA or RNA

3. Viruses are harmful meaning they can cause disease since they are infectious like biological beings.

4. Viruses can undergo mutations and alterations

Components of Viruses

Viruses can incorporate the subsequent components

 1. Nucleic acids 2. Capsid 3. Envelop

1. Nucleic acids: Viruses range from cell organisms as they comprise the simplest form of nucleic acid which can be either DNA or RNA. The viruses which comprise DNA are referred to as De-oxyviruses while those who comprise RNA are referred to as Ribo-viruses. The RNA that is found in viruses may be double-stranded (DS) e,g Reoviruses. The RNA that is found in viruses may be single-stranded (ss) e,g TMV, Influenza virus, Foot and mouth sickness virus, and HIV (Aids virus). The no. of Nucleotide pairs in molecule stages from 1000-250,000 pairs. the quantity of nucleic acid relies upon the dimensions of the virion, commonly the bigger the dimensions of the virion more is the quantity of nucleic acid.

2. Capsid: The capsid is formed up of numerous subunits of proteins known as Capsomers. The subunits are usually arranged in helical or polyhedral geometric forms. The number of proteins and the arrangement of viral capsomers are characteristic of specific viruses and thus can be useful in their identification and classification. e,g the total no. of capsomers in TMV virus is 2130.

3. Envelop: In a few viruses, the capsid is covered by an Envelop. The lipids and carbohydrates are contributed by the host cell. the proteins are coded by viruses. The viruses where the envelope is present are called Enveloped viruses e,g HIV. The viruses where the envelope is absent are called Nacked viruses e,g Polio viruses, Rio viruses, TMV viruses. The Envelope is also made up of subunits called peplomers.

Tobacco mosaic virus (TMV)

TMV was studied by D Iwanoski in 1892 and isolation from infected plants and crystallization was done by W.M. Stanley in 1935. TMV particles appear as a bundle of rods or needles under an electron microscope. Each rod is about 3000 in length and 170 in diameter and has a molecular weight of about 4,000,000. The protein coat is made up of 2130 identical protein subunits known as capsomers. tmvs RNA contains all of the genetic information needed for the manufacture of a complete TMV particle. The first visible symptom of TMV infection in the tobacco plant appears in the form of downward curling and distortion of young apical leaves the plant becomes stunted.

What form of the Virus is a Bacteriophage

The Bacteriophage refers to eaters of bacteria as they destroy bacteria. The Bacteriophages are obligate parasites and are found in habitats where bacteria can survive. The bacteriophages are also referred phages. the phages are known to occur in all bacteria. Most of the work has been done on the phages that attack Escherichia.

 Structure of Bacteriophage

It is named the Loli-Pop Construction. This form has a head and tail. It is also named Tadpole Construction. The tail in addition to the head is present. The tail is elongated, the head and tail are joined together with the help of the collar and neck. Around the tail, there is the presence of a sheath that is contractile from six edges, there is the presence of tail fibers on the lower side plate. there is the presence of structures called tail pins. so there are six tail fibers and six tail pins.

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