Virus | Structure and Classification | Biology | Extraclass

Описание: How Does the Deadliest Being on Planet Earth - The Bacteriophage look like? Extraclass.com will answers your question, but before that we should know what are viruses and how do viruses look like? What are the structure and types of viruses? envelope, capsid and nucleoid classifications of virus are shown in the video.


What are viruses?

All of us know about horrible diseases such as Polio, smallpox, hepatitis etc. which are caused by viruses.

In this video, we will learn about viruses and what makes them so dangerous to us.
Viruses are infectious agents, with a simple, acellular organisation.

The study of viruses is called virology
Viruses are the connecting link between the living and non-living organisms because they have properties of both living and non-living things.
Viruses are active only inside living cells and are obligatory intracellular parasites.

While outside of living organisms they act as a sand particle.
Let’s learn more about structure and types of viruses -
The structural components of viruses are envelope, capsid and nucleoid.
Envelope -

It is the outer thin loose covering composed of proteins from virus, lipids and carbohydrates from the host.

This layer may or may not be present. The envelope is present in HIV, Herpes virus.


There are many small projections called spikes present on the virus envelope.

These spikes only bind to specific receptors on the host cell.
(2) Capsid -

It is made up of small subunits of proteins called capsomeres which are an outer covering for the protection of the genetic material of a virus.


(3) Nucleoid or nucleic acid - It contains the viral genetic information encoded as DNA or RNA.
DNA containing viruses are called deoxy viruses.

These are of two types:-

(1) Double-stranded DNA (ds DNA) virus for example Pox virus, Cauliflower mosaic virus and Herpes virus.
(2) Single-stranded DNA (ssDNA) for example Coliphage phi into 174, M 13 phage.


RNA containing viruses or riboviruses are also of two types:-

(1)Double-stranded RNA (dsRNA) virus for example Reovirus, Wound tumour virus.
(2)Single-stranded RNA (ssRNA) virus, for example, TMV, Influenza virus, Foot and Mouth disease virus, Retroviruses (HIV) and M 12.


Let’s move on to learn about an important type of viruses called bacteriophages
Bacteriophage or bacterial viruses are the viruses that infect the bacteria.
They have a head and a protein structure that helps bind the virus to the host cells surface is the tail.

There are various parts of a bacteriophage:-
(1) Capsid head - Genetic material is packaged into the capsid head which is made up from protein.
(2) Collar - The sheath is connected to a thin disc or collar at the head end and to a base plate at the
tip end
(3) Sheath - It is an external contractile-envelope wrapping the tail tube in some viruses
(4) Baseplate - The baseplate of bacteriophage is a multiprotein molecular machine that controls host cell recognition.



(5) Tail fiber - It is a rod-like structure with a contour length of about 1400 Angstrom and a total mass of about
6,00,000 daltons



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