2 What is a Virus?disease-causing, nonliving particle composed of an inner core of nucleic acids surrounded by a capsidA virus replicates inside living cells called host cells
3 What is a Capsid?Outer coat of proteins that surrounds a virus' inner core of nucleic acidsThe arrangement of the capsid’s proteins determine the virus' shape
4 Why are Viruses Non-Living? Viruses are nonliving because:They don't exhibit all the criteria for lifeCriteria for life includes:Respiration, growth and developmentAll viruses can do is replicateReplication is making exact copies of themselves with the help of living cells
5 How are Viruses Named?Some Viruses are named after the disease they causeExample: Rabies VirusOther viruses were named for the organ or tissue they infect.Example: The Adenovirus effects the adenoid tissueRabies Virus
6 How does a Virus attach to a Host Cell? For a virus to replicate, it must enter a host cellWhen a virus’ proteins interlock with the receptor site, the virus is attached to its host cellThe attachment process is like two pieces of a jigsaw puzzle fitting together
7 Virus AttachmentEach virus has a specifically shaped attachment proteinViruses are species specificSome Viruses are cell-type specificExample: polio viruses normally infect only intestinal and nerve cells.
8 A Viral Replication Process Lytic Cycle:A Viral Replication ProcessAttachment: The Virus attaches to the Host CellEntry: The Bacteriophage injects its nucleic acid into the bacterial cellReplication : The host’s metabolic machinery makes the virus’ nucleic acid and proteins
9 Bacteriophage Also known as a phage Is a viruses that infects and destroys bacteria
10 A Viral Replication Process Lytic Cycle:A Viral Replication ProcessD. Assembly: New Virus Parts are madeE. Lysis and Release: The host cell breaks open and releases new virusesThis results in the killing of the host cell
11 Another Viral Replication Process… Of an Enveloped Virus:After attachment, the membrane of the host cell surrounds the virusThis produces a virus- filled vacuole inside the host cell's cytoplasm.The virus bursts out of the vacuole and releases its nucleic acid into the cell.
13 The Lysogenic Cycle: Begins the same way as the Lytic Cycle The virus attaches to the host cell and its nucleic acid is injected into the cell.Then the viral DNA is integrated into the host cell's chromosomesThis is done instead of immediately taking over the host's genetic material (As in the Lytic Cycle)This Cycle does not kill its host cell
14 RNA Viruses: Many Viruses, including HIV, are RNA viruses This means their only nucleic acid is RNAThe RNA virus with the most complex replication cycle is the RetrovirusThe Retrovirus - uses reverse transcriptase to make DNA from viral RNAthe retroviral DNA is then integrated into the host cell's chromosome
15 Reverse Transcriptase: Is an enzyme carried in the capsid of a retrovirus that helps produce viral DNA from viral RNAIf this enzyme is found in a person, it is evidence for infection by a retrovirus
17 Retrovirus Cycle:Once inside a host cell, the retrovirus makes DNA from its RNA with reverse transcriptaseReverse transriptase produces double- stranded DNA from the viral RNA.The double-stranded viral DNA becomes part of the host cell’s chromosome and it becomes a provirus
18 Provirus: viral DNA that is integrated into a host cell's chromosome It is replicated each time the host cell replicates
19 Human Immunodeficiency Virus (HIV) HIV infects white blood cells in humansThe infected cells still function normallyBecause the viral genetic material is a provirus that only produces a small number of new viruses at a timeAn infected person will not appear sickCan infect others with the virus through body fluids
20 Human Immunodeficiency Virus (HIV) Most people with HIV will get AIDSOver time, more white blood cells are infected and killedWhite Blood cells are essential to our immune systemTheir destruction reduces the body’s ability to protect itself from other viruses
21 Virus’ link to Cancer:Some viruses have been linked to certain cancers in humans and animalsViruses can disrupt the normal growth and division of cells in a hostThis causes abnormal growth and creates tumors
22 Prions:Are composed of proteins but have no nucleic acid to carry genetic informationAre thought to act by causing other proteins to fold themselves incorrectly, resulting in improper functioningResponsible for many animal diseasesExample: Mad Cow Disease
23 Viroids:Composed of a single circular strand of RNA with no protein coatShown to cause infectious diseases in several plants.Have less RNA than most viruses
24 Plant Viruses: There are more than 400 plant viruses Plant Viruses can cause stunted growth and yield losses in their host plants.The first virus to be identified as a plant virus was the tobacco mosaic virus
25 Plant Viruses: Do not undergo lytic or lysogenic phases Plant Viruses are named according to their host plant.Not all viral plant diseases are fatal or even harmful.The Mosaic virus, as seen in the following picture, cause patterns of color in the flowers of plants.