2Are Viruses Living or Non-living? Viruses are non livingThey have some properties of life but not othersThey can’t maintain a constant internal state (homeostasis) or reproduce without a host cell.
3What are Viruses?A virus is a non-cellular particle made up of a nucleic acid and protein coat (capsid) that can invade living cells.
4SmallpoxEdward Jenner (1796) developed a smallpox vaccine using milder cowpox virusesDeadly viruses are said to be virulentSmallpox has been eradicated in the world today
5Viewing Viruses Viruses are smaller than the smallest cell Viruses couldn’t be seen until the electron microscope was invented in the 20th century
6What is a Nanometer?A nanometer is a unit of measure. Just like inches, feet and miles. By definition a nanometer is one-billionth of a meter. A meter is about 39 inches long. That is a big number and when you divide a meter into one billion pieces, well that is very small.
9Characteristics Non living Noncellular Contain: 1. a protein coat called the capsid2. nucleic acid core containing DNA or RNACapable of reproducing only when inside a HOST cell
10Characteristics Some viruses are enclosed in an protective envelope CAPSIDSome viruses are enclosed in an protective envelopeSome viruses may have spikes to help attach to the host cellMost viruses infect only SPECIFIC host cellsDNAENVELOPESPIKES
11Characteristics Outside of host cells, viruses are inactive Lack ribosomes and enzymes needed for metabolismTo be able to reproduce they use the raw materials and enzymes of the host.EBOLA VIRUSHIV VIRUS
12Characteristics Some viruses cause disease Smallpox, measles, mononucleosis, influenza, colds, warts, AIDS, EbolaSome viruses may cause some cancers like leukemiaMEASLES
13Viral Shapes Viruses come in a variety of shapes Some may be helical shape like the Ebola virusSome may be polyhedral shapes like the influenza virusOthers have more complex shapes like bacteriophages
28Characteristics of Retroviruses/Latent Contain RNA, not DNAContain enzyme called Reverse TranscriptaseWhen a retrovirus infects a cell, it injects its RNA and reverse transcriptase enzyme into the cytoplasm of that cell and it is able to make DNA
29RetrovirusesHIV, the AIDS virus and human T cell leukemia virus are retroviruses
31Viral Attack Viruses are very specific as to which species they attack HOST specificHumans rarely share viral diseases with other animalsEukaryotic viruses usually have protective envelopes made from the host cell membrane
32Bacteriophage Replication-Lytic Cycle Bacteriophage inject their nucleic acidThey lysis (break open) the bacterial cell when replication is finished
33Lytic Cycle ReviewAttachment Phage attaches by tail fibers to host cellEntry Tail sheath contracts to force tail core and DNA into cellReplication Production of phage DNA and proteinsAssembly Assembly of phage particlesLysis/Release Phage breaks cell wall and releases new viruses
34Viral LatencySome viruses have the ability to become dormant inside the cellCalled latent virusesThey may remain inactive for long periods of time (years)Later, they activate to produce new viruses in response to some external signalHIV and Herpes viruses are examples
35Lysogenic Cycle Phage DNA or genome injected into host cell Viral DNA joins host DNA forming a provirusWhen an activation signal occurs, the phage DNA starts replicating
36Lysogenic CycleViral DNA (part of provirus) may stay inactive in host cell for long periods of timeProvirus Replicates during each binary fission in bacteria and Mitosis in Eukaryotic CellsOver time, many cells result which contain the provirus
38Viral LatencyOnce a provirus cell is activated, host cell enters the lytic cycleNew viruses form and the cell lyses (bursts)
39Latency in EukaryotesSome eukaryotic viruses remain dormant for many years in the nervous system tissuesChickenpox (caused by the virus Varicella zoster) is a childhood infectionIt can reappear later in life as shingles, a painful itching rash limited to small areas of the bodySHINGLES
40Latency in EukaryotesHerpes viruses also become latent in the nervous systemA herpes infection lasts for a person’s lifetimeGenital herpes (Herpes Simplex 2)Cold sores or fever blisters (Herpes Simplex1)SKIN TO SKIN CONTACTPASSED AT BIRTH TO BABY
41Interferon are naturally occurring proteins made by cells to fight viruses
42Strange and Unusual Virus Epidermodysplasia Verruciformis. Dr Gaspari, of the University of Maryland, concluded Dede’s affliction was caused by the Human Papilloma Virus (HPV), a fairly common infection usually causing only small warts.Caused by an extremely rare immune system deficiencyLeaves body unable to fight the warts.The virus was therefore able to “hijack the cellular machinery of his skin cells” causing them to produce tree-like growths known as “cutaneous horns”.“Tree Man” of Java