A virus is an infectious agent made up of nucleic acid (DNA or RNA) wrapped in a protein coat called a capsid. Viruses have no nucleus, no organelles, no cytoplasm or cell membrane—Non-cellular vs This is why it does NOT belong to any kingdom.
DISEASEVIRUSES AIDSHIV Wart Herpes Simplex Virus FluInfluenza MeaslesMorbillivirus. CancerHepatitis B Introduction – Structure – Replication – Virology – Medicine - Review Examples of some viral diseases:
Let’s look at the Defining Properties of Viruses 1.Viruses are parasites that invade cells 2.Viruses have either DNA (Deoxyribose Nucleic Acid) or RNA (Ribonucleic Acid) 3.Viruses direct the synthesis of new virus within a host cell. 4.Newly made viruses infect other cells. Introduction – Structure – Replication – Virology – Medicine - Review
Who do viruses infect? Viruses infect Bacteria – These viruses are called bacteriophages Viruses infect Plants – One example is the Tobacco Mosaic Virus Viruses infect Animals – One example is the flu Viruses usually infect a specific host including: Introduction – Structure – Replication – Virology – Medicine - Review
Capsid (protein coat) – inside contains either RNA or DNA 1.Bacteriophage—viruses that infect bacteria Tail fibers – allow attachment to the host
2. Viruses that infect plants Viroids Ex:Tobacco Mosaic Virus Tobacco Mosaic Virus (TMV) is an example of a virus with a helical structure. Protein subunits wrap around the spiraling RNA strand. Introduction – Structure – Replication – Virology – Medicine - Review This image taken using an Electron Microscope
Beyond Viruses…… VIROIDS: The Plant Invaders… A VIROID is a… VIR (virus) OID (like) particle. Viroids are“sub-viruses” composed exclusively of a single circular strand of nucleic acid (RNA) that codes for a single protein.
Surface Marker – allows for specific receptor binding of a host cell DNA or RNA Capsid (protein coat) 2. Viruses that infect animals Adenovirus Flu (influenza), pink eye, common cold Enveloped viruses are viruses which have a membrane coat surrounding the protein coat or capsid. These viruses are common in animal viruses, but are uncommon in plant viruses.
A PRION Has protein only, no DNA or RNA (cause of mad cow disease and Creutfeldt-Jacob disease in humans)—Prions (affects the brain and is always fatal) No DNA or RNA! Beyond Viruses…Beyond Viroids…
Cert ain viruses can only attack certain cell types. They are said to be specific. Surface Markers Receptor Sites Example: The rabies virus only attacks brain or nervous cells. Virus Cell
Surface Markers Receptor Sites Virus A virus recognizes cells it can infect by matching its surface marker with a receptor site on a cell. Cell
Replication Phases V - Release -Assembly of virus DNA and protein coat into whole new viruses -Leaving the cell http://www.cat.cc.md.us/courses/bio141/lecguide/unit2/viruses/adlyt.html Phase I Phase II Phase IV Phase VPhase III Introduction – Structure – Replication – Virology – Medicine - Review I, II, III - Viruses enter cell -Attachment to cell membrane -Penetration inside cell -Losing virus protein coat IV - Replication -Tricks cell into making more viral DNA -Tricks cell into making viral protein coat
Two “life” cycles: Lytic & Lysogenic Bacteriophages (viruses that attack bacteria) are often studied Replication is similar with many animal viruses Dozens of phage viruses attacking an E. coli bacteria cell The bacteria cell is destroyed and new viruses escape
1 st Step: Attachment –Virus lands on cell membrane –Virus attaches to a cell receptor –Virus acts as key; receptor acts as lock
2 nd Step: Entry –Virus enzyme weakens cell membrane –DNA/RNA enters the host cell Another way viruses may enter a cell… through phagocytosis
3 rd Step: Replication –Virus DNA/RNA uses ribosomes to make virus proteins –Virus proteins created by transcription/ translation transcriptiontranslation Viral DNAViral RNAViral Proteins
4 th Step: Assembly –Virus proteins are assembled into new viruses
5 th Step: Release –Virus enzyme causes cell membrane to LYSE (burst) –Viruses are released –Cycle repeats
1 st step: Attachment Same 2 nd Step: Entry Same
cell DNA Pro-virus 3 rd step: Replication –Provirus Created Virus DNA combines with cell DNA –Infected cell divides by mitosis and copies the provirus –Each new cell will contain the provirus Virus DNA Pro- virus
4 th Step: Assembly: new viruses are assembled in many cells 5 th Step: Release many cells burst releasing many more viruses
VIRUS HOST A living thing that provides a source of energy for a virus or an organism PARASITE Organisms that live on or near a host and cause it harm. A tiny, nonliving that invades and then multiplies inside of a cell. A virus that immediately goes into action. It begins to take over cell functions and produce the virus’s proteins and genetic material.These parts then assemble into new viruses. The viruses multiply like a copy machine left on. When it is full it bursts open – releases the new viruses and dies. Some viruses hide for a while and become part of the cell’s genetic material. It may stay inactive and “hidden” for years. Then under certain conditions it becomes active and acts like an active virus. Ex – cold sores
Importance: *Harmful Causes disease—pathogenic Disease producing agent—pathogen Human Diseases: Warts, common cold, Influenza (flu), Smallpox, Ebola, Herpes, AIDS, Chicken pox, Rabies Viruses disrupt the body’s normal equilibrium/balance Viruses can be prevented with vaccines, but NOT treated with antibiotics. Beneficial: Genetic Engineering—harmless virus carries good genes into cells. (antibiotics treat bacteria)
The End! And Review Viruses are very simple: a shell containing either DNA or RNA. They infect by hijacking cells’ machinery to force them to make more viruses. Viruses are tiny, even compared to a cell. Some viruses may prove useful in gene therapy as natural carriers of DNA that was specially designed to be good for a particular reason. Introduction – Structure – Replication – Virology – Medicine - Review
RNA virus Example: HIV Contain enzyme called “reverse transcriptase” Steps 1) Virus RNA enters host cell 2) Reverse transcriptase changes the virus RNA into DNA 3) Virus DNA combines with cell DNA (provirus created) 4) Cell divides and copies the virus 5) Eventually, the viral DNA becomes active
How is HIV contracted? High risk activities: – 1) Sex (oral, vaginal, anal) – 2) Sharing needles (tattoos, piercings, drugs) Low risk activities: – 3) Mother to child in womb – 4) Breast milk – 5) Blood transfusions High Risk Activities Low Risk Activities
HIV Prevention 100% Effective: Abstinence If sexually active: Latex condoms are the only forms of birth control that prevent STDs and pregnancy If drug user: Change needles
What is AIDS? Acquired Immunodeficiency Syndrome More than 1.2 million people in the United States are living with HIV infection Almost 1 in 7 (14%) are unaware of their infection. CDC estimates that 1,201,100 persons aged 13 years and older are living with HIV infection The estimated incidence of HIV has remained stable overall in recent years, at about 50,000 new HIV infections per year. In 2013, an estimated 47,352 people were diagnosed with HIV infection in the United States. In that same year, an estimated 26,688 people were diagnosed with AIDS. Overall, an estimated 1,194,039 people in the United States have been diagnosed with AIDS.
AIDS results when….??? “AIDS” refers to the late stage of HIV infection, when an HIV- infected person’s immune system is severely damaged and has difficulty fighting diseases and certain cancers. 1) Amount of T-cells drop (200 T-cells per 1mm³ blood) 2) Multiple symptoms/infections appear Rash, fever, headache, sore throat, swollen lymph nodes Therefore, the HIV virus causes the disease AIDS by killing your T-cells
More on AIDS Before the development of certain medications, people with HIV could progress to AIDS in just a few years. But today, most people who are HIV-positive do not progress to AIDS because of antiretroviral therapy (ART) You can keep the level of HIV in your body low. This will help keep your body strong and healthy and reduce the likelihood that you will ever progress to AIDS. It will also help lower your risk of transmitting HIV to others.
RNA or DNA core (center), protein coat (capsid) Copies itself only inside host cell--REPLICATION DNA or RNA NO Cell membrane, cytoplasm, genetic material, organelles Asexual or Sexual DNA and RNA YES—Multicellular Organisms YES Structure Reproduction Genetic Material Growth and Development Response to Environment Change over time Obtain and Use Energy