Is a Virus a Living Organism?• Properties of life• Cellular Respiration• Reproduction• Metabolism• Homeostasis• Heredity• Growth and development
Viruses are not living organismsViruses do not - Reproduce (replicate inside HOST) – Grow – Maintain homeostasis – MetabolizeViruses do – Infect cells and use the host cell to make more viruses – Cause disease in many organisms
Parts of a Virion (a virus particle)Nucleic Acid – RNA or • Capsid – protein coat that DNA surrounds the DNA or RNA in a virus
Parts of a VirionLipid Envelope– a lipid membrane around the capsid. Membrane is created by using the host cell membranes.Helps the virus enter new cells in the host. Membranes’ recognize each other.
What is DNA• DNA is found where in the cell?• Nucleus• DNA contains all genes and characteristics for an organism.• What are the four nucleotides that make up DNA?• DNA made up of A, T, C, G• Double strand
What is RNA• RNA carries info from DNA in nucleus to ribosomes where proteins (characteristics) are assembled.• RNA is made up of 4 nucleotides:• A, U, G, C and single strand• RNA is used to make what?• RNA makes protein
RNA or DNA?Viruses with RNA – Human immunodeficiency virus (HIV) – Influenza viruses (Flu) – RabiesViruses with DNA – Warts – Chickenpox – Herpes – Smallpox
Virus ShapesHelical Rodlike with capsid proteins winding around the core in a spiral Examples: Rabies, Measles
Measles• • Mild fever of 102 °F or lower • Headache • Stuffy or runny nose • Red, inflamed eyes • Enlarged, tender lymph nodes at the base of the skull, the back of the neck, and/or behind the ears • Fine, pink rashes that begins on the face and quickly spreads to the trunk, the arms, and then the legs before disappearing in the same sequence • Aching joints, especially in young women Causes Rubella is caused by a virus that is enveloped and has a single-stranded RNA genome. It is a contagious disease and can spread with the cough or sneeze of an infected person. It can alternately spread by direct contact with an infected persons respiratory secretions, including mucus. It can also travel from a pregnant woman to her unborn child (congenital rubella syndrome [CSR]). A person infected with rubella is contagious from one week before the start of the rash until about one to two weeks after the rash disappears
Herpes• Herpes simplex type 1: this type of Herpes virus causes the aggravating lip and mouth blisters and sores called cold sores or fever blisters, and technicall called Herpes labialis. It is HIGHLY infectious and can easily be spread by physical contact with an infected persons saliva• Herpes simplex Type 2: is the version of the virus that is responsible for genital herpes, the dreaded Sexually Transmitted Infection (STI) or Sexually Transmitted Disease (STD) - referred to as Herpes genitalis• Herpes zoster: Is the other major type of Herpes virus which affects many children in the form of Chicken Pox which also appears as a blister-like rash all over the body. You can also get Chicken Pox as an adult, but the illness can be more severe and unpleasant, so in many ways it is a good thing to get it out-of-the-way as a child. Although you will not get Chicken Pox again once your natural immunity has developed you will still have this Herpes virus in your system.• In later life if you become run down or highly stressed you may experience another form of outbreak of painful blisters that develop along certain nerve meridians around te torso, for instance, or in the scalp - this other herpetic illness that is called Shingles.
Virus ShapesPolyhedral Has many sides Most polyhedral capsids have 20 triangular faces.Ex. Herpes, Chickenpox, Polio
Polio• Poliovirus only circulates in humans. It is spread by the faecal–oral and oral-oral (respiratory) routes.• Infected people are most contagious shortly before and after onset of clinical illness when the virus is present in the throat and excreted in high concentration in the faeces.• Recipients of OPV (oral polio vaccine) can also pass on poliovirus to non-immune people as the virus persists in the throat for 1 – 2 weeks and is excreted in the faeces for several weeks.• Incubation period commonly 6–20 days with a range of 3–35 days.• Up to 95% of all polio infections are asymptomatic. Infected persons without symptoms shed virus in the stool.• Approximately 4%–8% of polio infections consist of a minor, nonspecific illness. Three syndromes observed with this form of poliovirus infection are upper respiratory tract infection (sore throat and fever), gastrointestinal disturbances (nausea, vomiting, abdominal pain, constipation or, rarely, diarrhoea), and influenza-like illness. These syndromes are indistinguishable from other viral illnesses.• symptoms of stiffness of the neck, back, and/or legs• Less than 1% of all polio infections result in flaccid paralysis. The frequency of paralytic disease increases with age. Paralytic symptoms generally begin 1 to 10 days after prodromal symptoms and progress for 2 to 3 days.• Generally, no further paralysis occurs after the temperature returns to normal.
Virus ShapesBacteriophages - Polyhedral capsid attached to a helical tail. Viruses that attack bacteria. (Ex. E. coli)
How do virusesreplicate?2 methods of replication: 1. Lytic Cycle – the virus enters the cell, replicates itself hundreds of times, and then bursts out of the cell, destroying it.
In the lytic cycle, thevirus reproducesitself using the hostcells machinery.The red spiral linesin the drawingindicate the virussgenetic material.The orange portionis the outer shellthat protects it.
Virus Replication2. Lysogenic Cycle – the virus DNA integrates with the host DNA and the host’s cell helps create more virus DNA. An environmental change may cause the virus to enter the Lytic Cycle.
In the lysogeniccycle, the virusreproduces byfirst injecting itsgenetic material,indicated by thered line, into thehost cells geneticinstructions.
Virus Reproduction• When a virus inserts its genetic material into a host’s DNA, it is called a provirus.• If virus has RNA and enters a host’s cells, it can sometimes turn its RNA into DNA.• Reverse Transcriptase – turns RNA into DNA (called retrovirus; ex. HIV); DNA instructs cell to make more viruses
Viruses Enter Living CellsViruses enter cells by punching a hole in the cells wall and injecting its DNA
Viruses Enter Living CellsViruses enter plant cells through tiny rips in the cell wall.Viruses enter animal cells by endocytosis.
Mutating virusesViruses can mutate when they copy the genetic material – Copy something wrong – Mistake proves useful – More powerful virus (more infectious)Viruses that mutate InfluenzaViruses don’t mutate often: HIV
Viruses are host cell specific.Most viruses are restricted to certain kinds of cells (those that infect plants cannot infect animal cells).Some viruses are also specific to certain species of animals.Why?Scientists think that viruses originated from escaped genetic material from host cells.
Hunt for new viruses• http://www.ted.com/talks/nathan_wolfe_hunts_
The spread of West Nile virus (1999 –2002) – bird, horse, mosquito or human
Viruses can be beneficial…Bacteriophages – attack & destroy bacteriahttp://dvc.infohio.org/index.php?option=com_content&view=article&id=11&Itemid=14&Baculovirus – ebola-like virus that attacks insects – Could use for pest control in crops • Cabbage loopers eat cabbage crops • Virus can kill pests in days
Also important…Any agent (not just viruses) that causes disease is a pathogen.Some viruses replicate very slowly and only cause damage when the conditions are “right”. (cold sores)
Human Immunodeficiency Virus (HIV) Acquired Immune Deficiency Syndrome (AIDS)
Basic Structure• Viral envelope – lipid bilayer; glycoproteins protrude from surface – Glycoproteins enable virus to recognize surface proteins of special immune cells and to enter the cell (like a key to the cell’s door)• 2 strands RNA – only 9 genes; 3 are found in many viruses (structural proteins)• Reverse Transcriptase – turns RNA into DNA (this makes HIV a retrovirus); DNA instructs cell to make more viruses
HIV Making Factories• Virus enters cell through endocytosis• Virus replicates RNA to DNA with reverse transcriptase
How Is HIV Spread?• Sexual contact• Sharing contaminated needles• Blood transfusions• Breast feeding (mother to baby)• Mother to baby during pregnancy or birth
• DNA enters nucleus & binds with host DNA •mRNA is created (carries instructions for making new viral proteins) and leaves nucleus •Uses host cell’s enzymes to make new viruses• New virions exit cell through exocytosis to infect other cells (notice cell isn’t destroyed)
Think about it…• In the US, there is better than a 1/1000 chance of contracting HIV during unprotected sex• A person can be contagious for more than 10 years before any sign of the disease is apparent• HIV becomes AIDS when the number of immune cells drops below a predetermined number• No one dies from HIV or AIDS; people die from secondary infections (ranging from the common cold to cancer)• More than 3 million people (size of Chicago) die each year • There are approx. 14,000 new cases of HIV worldwide every day