 3.a.1 – DNA, and in some cases RNA, is the primary source of heritable information (19.2).  3.c.3 – Viral replication results in genetic variation, and viral infection can introduce genetic variation into the hosts (19.1 & 19.2).

 An infectious particle consisting of nucleic acid enclosed in a protein coat  Characteristics: 1. Small size  Large - barely visible with the light microscope  Small - down to 20nm  Much smaller than cells (including bacteria) 2. Infectious 3. Reproduction 4. Alcohol resistance  Not immediately killed by alcohol (like your cells)

 Infection: ◦ Viruses cause many diseases ◦ They can be spread from one organism to another  Reproduction: ◦ Can not reproduce without a host ◦ Viruses are obligate parasites – must have host to survive

1. Genome - the genetic information 2. Capsids and Envelopes - the outer covering

 Protein shell that encloses the viral genome  Made from a large number of protein subunits  Number of kinds of subunits usually small  Often geometric in shape

 Membranes cloaking the capsids of some viruses  Made from host membrane, but may have virus- originated glycoproteins added

1. Cell Entry 2. Genome Replication 3. Capsid Protein formation 4. Self-assembly of offspring 5. Exit from Host

 Locate host by "Lock-and-Key” fit between virus proteins and cell receptor molecules  Infection - Begins when viral genome enters the cell  Some viruses can enter many hosts ◦ Ex: West Nile – mosquitoes, birds and humans

 This step begins the actual viral infection  Host cell is reprogrammed to copy virus genome  Use host DNA polymerase  Use virus enzymes to copy RNA to DNA  Use host's resources to make copies of viral proteins

 Host's protein synthesis machinery used to make virus proteins

 genome + capsid  virus  Particles usually assemble spontaneously

 Host cell may burst or lyse, releasing the virus  May "bud-off" host membrane, forming envelopes around the capsids

 Best understood of all viruses  Called phages  May show two types of virus life cycles: ◦ Lytic Cycle ◦ Lysogenic Cycle

 Virus reproductive cycle that kills the host cell  Note - the previously described virus life cycle was a Lytic Cycle

 Uses Lytic Cycle  Example of an Virulent Virus (a virus that only uses the lytic cycle)  Has about 100 genes  Completes cycle in minutes

 Virus reproduction that doesn't immediately kill the host cell ◦ Usually doesn’t kill the host AT ALL  Viral DNA is inserted into the host DNA, but not expressed

 Belong to several viral classes  Specific Interests: 1. Viruses with envelopes 2. RNA viruses  Ex. of Infections caused by animal viruses: Cold sores/canker sores, influenza, common cold

 Use nuclear membrane  Causes: cold sores, shingles, chicken pox, mononucleosis  Viral DNA integrated into Host DNA as a provirus  Shows both lytic and lysogenic life cycles

 Classes III – VI  Ex: yellow fever, rubella, common cold, SARS, ebola  Class VI - Retrovirus - use Reverse Transcriptase to make DNA from an RNA template.

 HIV - causes AIDS  Retrovirus from chimps  Destroys the body’s immune system, allowing other diseases to kill

 Measles  Polio  Smallpox  Influenza

 Vaccines (preventative)  Some Drugs ◦ Ex: Ara-A Acyclovin(Herpes treatment) ◦ Ex: AZT – HIVirus  Comment - some treatments are working on the reverse transcriptase  Problems: ◦ Since viruses work within a host cell, they are very difficult to treat ◦ Best Treatment – prevention ◦ Can also cause cancer

 Infectious particles of naked RNA  Affect plants  Similar to viruses, but lack a capsid  Ex: ◦ Coconut Blight ◦ Chrysanthemum Wilt

 Infectious protein particles  Affect animals  Cause “mad-cow” and Creutzfeldt-Jakob disease  Transmitted in food  Slow-acting  Virtually indestructible  Protein folding problem?

 DNA circle (Chromosome)  Plasmids - Small circle of DNA that is independent of the chromosome  Carries a small number of traits

1. Transformation 2. Conjugation 3. Plasmids  This is how bacteria mix genetic material into new combos

 Alteration of a cell's DNA by the uptake of foreign DNA  Ex: Griffith's experiment

 Direct transfer of genetic material between two bacterial cells  Bacterial "sex”  Used to map genetic sequences in bacteria

 Small circular piece of DNA  Carry many important traits  Ex: Fertility Factor Antibiotic Resistance (R Plasmids)  Virus movie 