Today’s lesson, we cover: 1. viruses 2. viroids 3. Prions All are infectious agents

VIRUSES Viruses are non-living. Virus (Latin): meaning poisonous slime of plant or animal origin Viruses are non-living. 1. Acellular: lack cell membrane and organelles 2. No metabolic activity 3. Lack energy generating system 4. They are obligate parasites - only capable of reproduction in a host cell. 5. Genetic material: DNA or RNA, housed within a protein coat called a capsid Virus (Latin): meaning poisonous slime of plant or animal origin 1nm = 1000 um A complete virus particle is called a virion. http://www.ncbi.nlm.nih.gov/books/NBK8174/ Virus size: 10-300 nm

Virus Characteristics (cont.) Viruses that infect animal cells can: Disguise from the host’s immune system by “wearing” an envelope made of the host’s cell membrane Protein spikes protrude outward to help with attachment of the virus to the host cell. Blow up next page for student Influenza viruses (100nm each), with capsid and membrane visible

Viruses are classified based on 1. Capsid’s size and shape (Cylindrical, Polyhedron, Enveloped, Binal (complex) shape) 2. Types of genetic materials (i.e. DNA or RNA) 3. The number of strands in Nucleic Acid - either single stranded or double stranded form 4. Nature of host (plant, animal or bacteria) 5. Presence or absence of envelope VIRUS CLASSIFICATION Polyhedron The viral genome, often with associated basic proteins, is packaged inside a symmetric protein capsid. The nucleic acid-associated protein, called nucleoprotein, together with the genome, forms the nucleocapsid. In enveloped viruses, the nucleocapsid is surrounded by a lipid bilayer derived from the modified host cell membrane and studded with an outer layer of virus envelope glycoproteins. Icosahedron is a polyhedron with 20 triangular faces, 30 edges and 12 vertices. Tobacco Mosaic Virus. This tobacco mosaic virus was the first virus to be discovered. It was first seen with an electron microscope in 1935. Cylindrical/helical Binal (irregular) shape Spherical http://www.youtube.com/watch?v=7iVm1uEIyP0

PRACTICE IDENTIFY VIRAL SHAPES Influenza spherical; 2. ebola viruses:u shaped 3. tobacco mosaic viruses: helical/cylindrical News on ebola: causes haemorrhage http://www.scripps.edu/news/press/2013/20130815ollmann-saphire.html Like a ‘Transformer’, this protein of the Ebola virus adopts different shapes for different functions, it revises a central dogma of molecular biology—that a protein molecule has one shape that predestines one biological function. EBOLA VIRUS

BACTERIOPHAGE STRUCTURE Bacteriophage: is a virus that infects bacteria capsid (protein coat) nucleic acid tail tail fibres cell membrane viral RNA/DNA being injected into host cell

Virus Reproduction Incubation period: time taken before symptoms show 2 possible cycles: lytic and lysogenic 1. The LYTIC Cycle (shorter incubation period) Share one important trait with living thing: they reproduce E.g. Bacteriophage T4 infects E. coli

B. Insertion A. Attachment E. Lysis & Release D. Assembly bacterial DNA virus - Host’s DNA/RNA get digested - Virus injects its nucleic acid into host cell Viral DNA Bacterial host cell E. Lysis & Release Cell lysed due to viral enzyme; new phage go on infect other hosts C. Replication D. Assembly The host’s metabolism replicates the viral RNA/DNA New viral particles are assembled See blown up version of this page

Virus Reproduction 2. The LYSOGENIC cycle (longer incubation period) provirus A- Attachment & entry: The virus invades a host cell and injects its DNA (or RNA) into the host. B- Integration The viral DNA is merged with the host DNA. C- Multiplication of Genome Viral DNA duplicates as host cell divides The viral DNA remains dormant for a long period of time (provirus) D- Cell division As host cell divides, viral particles also get made After this point, the virus may enter lytic cycle by an environmental trigger

Bring 2 cycles together

Compare lytic and lysogenic cycles Lytic cycle Lysogenic cycle Fate of virus DNA/RNA after infecting the host Take over host DNA Becomes part of host DNA Incubation time in host cell Short; new viruses released within host’s lifetime or in the next generation Long; new viruses released after several generations of host Onset of viral diseases symptoms Immediate delayed

VIRUSES and DISEASES Caused by herpes simplex virus (a DNA-containing virus). The sores appear during lytic cycle The sores disappear (when the viruses is in its provirus stage) on the skin throughout the person’s lifetime. Lifetime latency is established when virus migrates to trigeminal nerve ganglion Use Polysporin to make the sore disappear quicker; no cure still http://www.mayoclinic.com/health/cold-sore/DS00358 Cold sores are caused by a herpes simplex virus (HSV-1) closely related to the one that causes genital herpes (HSV-2). Both of these herpes simplex viruses can affect your mouth or your genitals, and can be spread via oral sex. Canker sore: not caused by herpes virus COLD SORE (Kissing Disease) Virus is periodically reactivated in times of physical or emotional stress A different kind of sore: canker sore

VIRUSES and DISEASES AIDS (acquired immune deficiency syndrome): Caused by HIV- a retro virus The HIV destroys the body’s T-lymphocytes, which help fight off infections from other diseases When leaving the host cell, new HIV take a piece of the host cell membrane to disguise themselves from the host body’s immune system. epidemic  vs Pandemic Epidemic: seasonal outbreak affecting smaller # of living things than a pandemic Pandemic: global scale outbreak http://www.youtube.com/watch?v=9leO28ydyfU HIV (AIDS) HIV video: http://www.youtube.com/watch?v=v_AUuMbtO-E

What is a retro-virus? A virus that use an enzyme called reverse transcriptase to converts its RNA into DNA once inside a host cell https://www.youtube.com/watch?v=dn1tNIrMPRk

can be used to make lots of copies of desirable genes VIRUSES and BIOTECHNOLOGY can be used to make lots of copies of desirable genes

Viruses can precisely insert their DNA/RNA into host’s DNA can be used in ‘gene therapy’ to repair faulty genes The virus must be disarmed before use Virus carrying the desired gene is allowed to infect the patient’s stem cells. VIRUSES in GENE THERAPY Virus is another famous vector beside bacteria. Used instead of plasmid when the DNA strand to be manipulated is quite long Genetically engineered viruses can be used to deliver healthy working alleles of gene to the a human chromosome. Shown here as a spherical virus but actually a T4 phage Why injected the stem cell with the recombinant DNA into bone marrow? Because you need the healthy genes to be able to multiply over the course of the person’s life so stem cells in bone marrow is the best location. Stem cells give rise to other cells that become specialized later on that now can contain the healthy version of the gene

How vaccines work? 1 2 3 How vaccine works- from the Gates Foundation http://youtu.be/JZvpF6gaGH4

Vaccines antigens Vaccines are mixtures of dead or weakened forms/parts of dangerous viruses When inside a host, the antigens on the surface of the weakened viruses trigger white blood cells to produce antibodies, without causing an infection Antibodies are chemicals produce by your body to recognize foreign antigens attenuated  = modified or weakened viruses or parts These antibodies has long lasting memories that allows the immune system to react quickly if it contacts the real virus NPR Flu Attack video: http://www.youtube.com/watch?v=Rpj0emEGShQ

Vaccines antibody Foreign Invader macrophage antigen White Blood Cell 19

Mis-shaped potatoes caused by viroids Smaller than virus, with no capsid Single stranded, circular RNA that do not code for proteins (unlike viruses; viral RNA do code for proteins) Size of viroids: ~359 nucleotides; 10 molecules enough to infect plants Mis-shaped potatoes caused by viroids Viroids under microscope

Prions Are single proteins Found in brain of infected animals Once eaten, prions go to the animal’s brain Cause diseases by interacting with normally shaped proteins causing them to become abnormal and infectious Responsible for brain diseases such as mad cow diseases in cow, scrapie in sheep and Creutzfeldt-Jakob disease in human BSE = bovine spongiform encaphelopathy or mad cow disease

News Update Univ. of Cadiff- School of Med

http://youtu.be/jFpwHe6KjDA