LEC 2, Medical biology, Theory, prepared by Dr. AYAT ALI

Transcription

1 General Characteristics, Structure and Taxonomy of Viruses Viruses 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.. These microorganisms belong to the family of viridae and Genus of virus. 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. 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. General Characteristics:- Viruses are much smaller than prokaryotic or eukaryotic cells. Unlike cells, they have a generally simple and static structure. They have no metabolic system of their own. They depend upon the machinery of the host cell for replication (obligate intracellular parasites (. They have either DNA or RNA genomes, but lack ribosomes and other factors needed for translation. Thus, they are dependent on the host cells for production of viral proteins. Their genomes encode minimal information to ensure the following:

2 1) genome replication and packaging 2) production of viral proteins 3) subvert cellular functions to allow the production of virions. Some viruses (bacteriophages) infect prokaryotic cells, while others infect eukaryotic cells. Some viruses destroy cells, producing disease; other persist in infected cells either in a latent or persistent state; and other may cause cellular malignant transformation. 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. 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. Viral Structure Viruses are minimally composed of a nucleic acid genome (DNA or RNA) and a protein coat. Many viruses contain an external membrane called an envelope. The nucleic acid plus the capsid shell of a virus particle is often called nucleocapsid. The simplest viruses are those LOST of envelope with singlestranded DNA or RNA

3 Enveloped viruses contain an external membrane surrounding the nucleocapsid). The viral envelope is derived from host cell membranes (nuclear, Golgi apparatus, endoplasmic reticulum or plasma membrane). As such, it is composed by a lipid bilayer, with virus-encoded proteins inserted on it. Some viruses, such as bacteriophages, have complex protein tails that are required for attachment and/or penetration of viral DNA into susceptible host cells. Shapes of Viruses 1-Structure of Ebola virus :-They are helical in shape like the Ebola virus. 2-Structure of influenza virus :-They are polyhedral shapes like the influenza virus

4 3-Structure of bacteriophages :- They are complex in shapes like bacteriophages. 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. Different Types of Viruses 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.

5 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: Polio:- 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 poliovirus and it is transmitted both by orally and fecal routes. Poliovirus 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. Precautions: This disease can be controlled by immunization the infants with polio vaccine.

6 Measles :- 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. Precautions: This disease can be controlled by vaccinating the infants with the vaccination active and passive immunization. Structure of Viruses (MEASLES) AIDS:- AIDS 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.

7 Modes of transmission: a. By unprotected sexual intercourse. b. Contact with an infected blood. c. Breastfeeding d. Injecting drugs. Symptoms: Diarrhea, fatigue, fever, weight loss, dry cough, shortness of breath, night sweats, difficulty in concentrating, 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. Precautions: Avoid sharing personal items, such as tooth-brush, intravenous needles, syringes, cotton, drugs.