Virus, Difference Between Virus & Bacteria, DNA & RNA Viruses

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Coronavirus disease 2019 (COVID-19)

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In the five-kingdom biological classification of Whittaker, there is no mention of acellular organisms like virus & viroid, & cellular organisms like lichens.

Viruses

Viruses did not find a place in classification since they are not truly ‘living’, if we understand living as those organisms that have a cell structure.
The viruses are non-cellular organisms that are characterized by having an inert crystalline structure outside the living cell.
Viruses are obligate parasites. Once they infect a cell, they take over the machinery of the host cell to replicate themselves, killing the host.
The name virus that means venom or poisonous fluid was given by Pasteur.
In addition to proteins, viruses also contain genetic material, that could be either RNA or DNA.
No virus contains both RNA & DNA.
In general,
- viruses that infect plants have single-stranded RNA &
- viruses that infect animals have either single or double-stranded RNA or double-stranded DNA
- bacteriophages (viruses that infect bacteria) are usually double-stranded DNA viruses.
The protein coat called capsid made of small subunits called capsomeres protects the nucleic acid.
These capsomeres are arranged in helical or polyhedral geometric forms.

Viruses cause diseases like mumps, smallpox, herpes & influenza. AIDS is also caused by a virus.
In plants, the symptoms can be mosaic formation, leaf rolling & curling, yellowing & vein clearing, dwarfing & stunted growth.

Viroids are infectious agents that are smaller than viruses.
A viroid is a free RNA, it lacks the protein coat that is found in viruses, hence the name viroid.
The RNA of the viroid was of low molecular weight.
Viroids cause potato spindle tuber disease.

Virus	Viroid
It is a nucleoprotein particle.	It is an RNA Particle.
Nucleic Acid can be DNA or RNA.	Viroid is formed of only RNA.
A protein covering of coat is present.	A protein coat is absent.
Virus has a larger size.	Viroid has a smaller size.
Virus infects all types of organisms.	Viroid infects only plants.

Bacteria are single-cell, living organisms that can survive without a host.
They can live on surfaces, in soil, in water, & in the air.
You can kill them by messing with their ability to do cellular respiration or their ability to grow.
Antibiotics are used to treat bacterial infections because antibiotics kill bacteria.
Hence Antibiotics are useless against viruses.
There are some antiviral drugs that help protect you from a viral infection.
Antivirals either make it harder for the virus to get into the cell or they prevent the virus from reproducing once they are inside of your cells.
Most bacteria reproduce by simply dividing into two.
Bacteria can cause diseases such as pneumonia & food poisoning.
However, not all bacteria are bad. In fact, some friendly types actually help protect us from the disease.

Virus	Bacteria
They are very Small	They are larger in size as compared to virus
Non-Cellular	Single-Celled
Have no metabolism of their own	Have metabolism of their own
Take no food by any method	Take food by absorption
Do not grow & do not divide	Grow in size & divide to produce more bacteria (by Cell-Division)
Command the host cell to produce virus	They can reproduce by their own
Can be crystallised	Cannot be crystallised
All produce diseases in man, animals & plants	Some are harmless, some useful & some are disease-causing
Contains only genetic material & protective coating	Contains various cells subunits or organelles such as cytoplasm & cell wall which all perform specific functions
They have simpler DNA (if their genetic material is DNA)	They have more complex DNA
Multiply faster than bacteria	Multiply slower than Viruses
They are Non-Living	They are living
Vaccines prevent the spread & antiviral medicines help to slow reproduction but cannot stop it completely	They can be treated with Antibiotics
Example– Common Cold, Flu & Sore Throat	Example– Strep Throat, Tuberculosis, Whooping Cough

A virus can self-replicate inside a host cell.
The infected cells may produce thousands of new copies of the original virus at an extraordinary rate.
The genetic material of a virus can be either DNA or RNA.
The viruses that contain DNA as their genetic material are called the DNA viruses.
RNA viruses, on the other hand, contain RNA as their genetic material.
DNA viruses are mostly double-stranded while RNA viruses are single-stranded.
RNA mutation rate is higher than the DNA mutation rate.
DNA replication takes place in the nucleus while RNA replication takes place in the cytoplasm.
DNA viruses are stable while RNA viruses are unstable.
Antigens: A substance which the body recognizes as alien & which induces an immune response.
Antibodies: A blood protein produced by the body in response to & counteracting an antigen.

DNA	RNA
Deoxyribonucleic Acid	Ribonucleic Acid
Double-Stranded	Single Stranded
Deoxyribose Sugar	Ribose Sugar
Self Replicate	Can’t Self-Replicate It is synthesized from DNA when required
Occurs inside the nucleus & of cell & some cell organelles (mitochondria) but in plants, it is present in mitochondria & plant cell	It is found in the cytoplasm of the cell but very little is found inside the nucleus.
DNA is the genetic material in all living organisms	RNA is the genetic material in some viruses
Long Polymer Chain	Shorter Polymer Chain
Life of DNA is longer	Its life is short
DNA occurs only in one form in any organism	3 types of RNA are present in an organism: – mRNA, rRNA, tRNA
DNA is functional in the transmission of genetic information It forms as a media for long-term storage	RNA is functional is the transmission of the genetic code that is necessary for the protein creation from the nucleus to the ribosome
Bases present are Adenine, Guanine, Cytosine, & Thymine	Bases present are Adenine, Guanine, Cytosine & Uracil

Gene	Genome
A gene is a part of DNA Molecule.	The genome is total DNA in a cell.
The hereditary element of genetic information.	All set of nuclear DNAs.
Encodes protein synthesis.	Encodes both proteins & regulatory elements for protein synthesis.
Length is about a few hundreds of bases.	Length of the genome of a higher organism is about billion base pairs.
A higher organism has about thousands of genes.	Each organism has only one genome.
Variations of the gene named alleles can be naturally selected.	Horizontal gene transfer & duplication cause large variations in the genome.