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

Coronavirus disease 2019 (COVID-19)

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  • 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.



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.

Difference Between Virus & Bacteria

  • 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.



They are very Small

They are larger in size as compared to virus



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

Difference Between DNA & RNA Viruses

  • 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.

Difference between DNA vs RNA



Deoxyribonucleic Acid

Ribonucleic Acid


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

Difference between 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.

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