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Viruses are non-cellular organisms, which made up of genetic material and protein that can invade living cells. These micro organisms belong to the family of viridae and Genus of virus.
A virus is non-cellular organisms made up of genetic material and protein that can invade living cells. They are considered both a living and non living things. In the year 1897, a scientist named Beijerinck discovered and coined the term virus. The term virus is derived from Latin word-“virus” means poison. Later in the year 1935, a scientist named Wendell Stanley discovered that these viruses are composed of nucleic acids, protein and lips. The study of viruses is called as virology.

Viruses are very small and they measured in nanometers. They can only be seen with an electron microscope. They are composed of a core of DNA or RNA surrounded by a protein coat they can only reproduce by infecting living cells. Their size ranges from 20 nanometers to 250 nanometers.

Structure of Viruses

Structure of Viruses


Shapes of Viruses

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Below you could see shapes of viruses

Structure of Ebola virus

They are helical in shape like the Ebola virus.

Ebola Virus

Structure of influenza virus

They are  polyhedral shapes like the influenza virus

Influenza Virus

Structure of bacteriophages

They are complex in shapes like bacteriophages.
Structure of Bacteriophages

Characteristics of Viruses

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Below you could see characteristics of viruses
  • They are enclosed in a protective envelope.
  • They have spikes, which helps them to attach to the host cell.
  • They are non cellular.
  • They do not respire, do not metabolize and do not grow but they do reproduce.
  • They contain a protein coat called the capsid. 
  • They have a nucleic acid core containing DNA or RNA.
  • Ribosomes and enzymes are absent, which are needed for metabolism.
  • They are considered both as living and non living things, as viruses are inactive when they are present outside of host cells and are active in side of host cells. As they make use of raw materials and enzymes of the host cell to reproduce and causes several infections.

Advantages of Viruses

They are use full in delivering genes to target cells and play a vital role in and gene therapy researches.

Disadvantages of Viruses

There are many pathogenic viruses, which causes harm for human beings, plants and animals. In human beings the diseases caused by viruses are: HIV, influenza, herpes, hepatitis small pox, cowpox, etc. The diseases caused by viruses in plants are tobacco mosaic viruses, etc. The diseases caused by bacteria in animals are bovine tuberculosis and etc.

Different Types of Viruses

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Diseases can be defined as a disorder, infections or malfunction of the cells, tissues, organs and different parts of our body. If these diseases are left unrecognized or not diagnosed on time, results to the death of an individual.

There are many diseases, which varies in modes of transmission, diagnosis, symptoms and treatments. There are two types of diseases.

Infectious diseases: These are the diseases, which are caused by pathogenic organisms like: bacteria, viruses, fungi, protozoa, etc. They are spreading disease and can be infected by eating, touching, drinking or by breathing something that contains germs. These diseases can also spread when we come in contact with someone who has been infected.

Non-infectious diseases: These are the diseases, which are neither caused by any pathogenic organisms, nor by spreading from an infected person. These diseases are generally caused by genetical disorder, environmental factors or by deficiencies in nutrition.

Viruses are non living strands of genetic material, which are coated with a protein coat. They are non motile and cannot reproduce by their own, hence they are considered non living.

Different types of viruses and diseases caused by them:


It is a viral infection, which is caused by a polio-virus that attacks and infects the nerve cells of the brain and spinal cord, which results in severe injuries and paralysis.

  • Modes of transmission: It is a viral infection, caused by polio-virus and it is transmitted both by orally and fecal routes. Polio-virus lives in the throat and intestinal tract of a human body.
  • Symptoms: fever, headache, nausea and vomiting. These patients develop a higher fever and severe headache with stiffness of the neck and the back.
  • Diagnosis: Viral isolation and other fluid tests like: blood test, throat secretion and cerebrospinal fluid.
  • Treatment: Bed rest, close monitoring of respiratory and cardiovascular functioning, respiratory therapy may be needed, depending on the severity of patients.
  • Precautions: This disease can be controlled by immunization the infants with polio vaccine.

Structure of polio viruses

Structure of Polio Viruses


 It is an acute, highly contagious viral disease caused by measles virus. It is an infection to the respiratory system.
  • Modes of transmission: It is an air-borne disease and spreading disease. It can be spread by eating, touching, drinking or breathing something that contains this virus.
  • Symptoms: Runny nose, dry cough, swollen eyelids with sensitivity to light, sneezing, fever, grayish-white spots found usually in the mouth, cheeks and throat. 
  • Diagnosis: Blood test.
  • Treatment: It can be easily cured by proper and supportive care taken at home.
  • Precautions: This disease can be controlled by vaccinating the infants with the vaccination active and passive immunization.

Structure of measles virus.

Measles Virus


 AIDS stands for “Acquired immune deficiency syndrome”. It is a viral infection, which is caused by HIV-human influenza virus.
AIDS is the final stage of HIV infection. A person  suffering with AIDS has a very weak immune system and the ability to fight against infection is very low.

  • Modes of transmission: 
           a. By unprotected sexual intercourse.
           b. Contact with an infected blood.
           c. Breastfeeding  and 
           d. Injecting drugs.

  • Symptoms: Diarrhea, fatigue, fever, loss of appetite, weight loss, dry cough, shortness of breath, night sweats, difficulty in concentrating, numbness, etc.
  • Diagnosis: The diagnosis for aids includes some preliminary tests like blood test and urine test. Other test like ELISA, PCR, RIP and western blotting is also used to diagnosis HIV.
  • Treatment: The most effective treatment for HIV is highly active anti retro-viral therapy.
  • Precautions: Avoid sharing personal items, such as tooth-brush, intravenous needles, syringes, cotton, drugs, razors, etc. As it may be contaminated with blood, semen, or vaginal fluids and by having safe sex.
Structure of HIV virus.

Structure of HIV Viruses
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