12.2 VIRUSES

1. BY: Elaine Cheng & Mohamed Elmi FOR: Ms.Khadem SBI3U1-01 April 08, 2011 12.2 VIRUSES

2. WHAT IS A VIRUS? • A virus is a small infectious agent that can replicate only inside the living cells of organisms • Most viruses are too small to be seen directly with a light microscope. • Viruses infect all types of organisms, from animals and plants to bacteria and archaea.

3. … continued Viruses are found in almost every ecosystem on Earth and are the most abundant type of biological entity. The study of viruses is known as virology, a sub-speciality of microbiology.

4. … continued • Virus particles (known as virions) consist of two or three parts: the genetic material made from either DNA or RNA, long molecules that carry genetic information • The average virus is about one one-hundredth the size of the average bacterium.

5. Types of viruses: • Viruses spread in many ways • viruses in plants are often transmitted from plant to plant by insects that feed on the sap of plants • viruses in animals can be carried by blood-sucking insects • In other words, known as vectors • Influenza viruses are spread by coughing and sneezing. HIV is one of several viruses transmitted through sexual contact and by exposure to infected blood.

6. DNA viruses • The lytic cell is usually considered as the main method of viral reproduction. • Ends in the lysis of the infected cell releasing the progeny viruses that will spread and infect other cells. • Attachment – the virus attaches itself to the host cell • Injection – the virus inserts its genetic material into the host cell • Integration – the genetic material tells the cell what to do • Replication – the host cell builds parts of the virus • Assembly – the cell assembles the replicated parts into progeny viruses • Lysis – the cell breaks open and each replicated virus can now infect other cells.

8. … continued • The lysogenic cycle is complementary to the lytic cycle for viral entry and reproduction within cells. • Common to both animal viruses and bacterial phages. • Viral genome enters cell • Viral genome integrates into host cell genome • Host cell DNA polymerase copies viral chromosomes • Cell divides, and virus chromosomes are transmitted to cell’s daughter cells • When virus is “triggered”, the viral genome detaches from the host cell’s DNA and enters stage 2 of the lytic cycle.

9. RNA viruses • Many viruses such as tobacco mosaic virus have RNA rather than DNA as their genetic material. • In normal cell process molecules of RNA, direst all cell activities. • Some proteins function as enzymes to control chemical reactions; other proteins provide structural characteristics to a particular cell. • The life cycle of RNA viruses is also similar. • It gives the potential to outwit the immune system.

11. Retroviruses • A retrovirus is an RNA virus that is replicated in a host cell via the enzyme reverse transcriptase produce DNA from its RNA genome. • Then in incorporated into the host’s genome by an integrase enzyme. • Replicates as part of the host cell’s DNA, which is integrated into the cell’s genome (becomes provirus), then undergoes the usual transcription and translational process. • Retroviral protein is: RNA > DNA > RNA > Protein

12. Viral Diseases • A viral infection is any type of illness or disease caused by a virus, type of microbe. • Microbes are tiny organisms that cannot be seen without a microscope and include bacteria, fungi, and some parasites • A viral infection may also be caused by an insect bite. • A viral infection occurs when a virus enters the body through such processes as breathing contaminated air, eating contaminated food, or by having sexual contact with a person who is infected with a virus. • In a viral infection, the virus invades the inside of the body’s cells in order to reproduce. • A virus then spreads to other cells and repeats the process

13. … continued • Symptoms of viral infection vary depending on the type of infection, the area of the body that is infected, the age and health history of the patient and other factors. • It can also resemble symptoms of other diseases, such as bacterial infections. • Symptoms may affect almost any area of the body or body system. • Fever, chills, headache, stiff neck, irritable, enlarged glands, diarrhea, nausea, vomiting, rash, abdominal pain, sore throat, ear pain, cough, weight loss, fatigue, body aches, and other flu-like symptoms.

14. HOPE YOU LEARNED A LOT! NOW YOU KNOW HOW TO AVOID VIRUSES! BY: ELAINE CHENG MOHAMED ELMI