Bio Unit 13

• Viruses can affect all living things in both good and bad ways
• 1872- Mayer and Koch found that a filter able agent caused disease in tobacco. it passed through filters and couldn’t be grown in a lab
• 1936- first virus was isolated from diseased tobacco plants (Tobacco Mosaic Virus)
• Viruses can be seen using an electron microscope (too small for light microscope)
• Viruses can have either dna or rna inside. and on the outside it has a protein coat (capsid)
• Protein Coat Shapes: spherical, cubical, polyhedron, and rodlike
• protein coats may also have an outside membrane (envelope)
• Viruses reproduce at a fantastic rate but only in living host cells
• Viruses are acellular. They have no cytoplasm, metabolism, or membrane bound organelles.
• Viruses never contain both dna and rna
• Many scientists consider viruses nonliving
• Lytic cycle- virus takes over all metabolic activities in the host, makes copies, then destroys the cell
• Steps 1 in Lytic Cycle is Attachment
• Step 2 in Lytic cycle is the entry of dna into the host
• Step 3 in lyric cycle is replication of viral pieces
• Step 4 in lytic cycle is assembly of new viruses
• Step 5 in lytic cycle is release of new viruses into the host (Lysis)
• Lysogenic Cycle- viral dna becomes integrated with the hosts (provirus). Will not exist without the lytic cycle
• Motto of Lytic Cycle: get in, take over, get out
• Motto of lysogenic cycle- get in, dormant, take over, get out
• Lysogenic cycle step 1- bacterial cell becomes host
• Lysogenic cycle step 2- injection of viral genome (dna)
• Lysogenic cycle step 3- viral dna will find bacterial dna
• Lysogenic cycle step 4- integration into host cells dna
• Lysogenic step 5- replication of cells (dormant)
• Lysogenic step 5- trigger to enter lytic cycle (replication of viral pieces)(Lysis)
• RNA Viruses (Retroviruses)- virus with RNA that can invade cells with DNA
• RNA undergoes reverse transcription to produce double stranded DNA and provirus in host
• RNA viruses have a high mutation rate
• there’s no good proof reading mechanism in RNA viruses so this makes many different strains of the virus.
• Many different strains of RNA viruses make vaccines difficult to develop
• Classify- to group things together based on similarity
• We classify to make things easier to identify
• There are over 1.6 million species and more are discovered each year
• Classification serves as an an organization system for all existing organisms
• The science of classifying is taxonomy
• Aristotle’s early classification had 2 groups: 1. Plants = green, not mobile 2. Animals = not green, mobile
• Tools used to classify organisms today: comparative anatomy, biochemistry, embryology, molecular basis, and phylogeny
• Comparative anatomy- comparing physical structure
• Biochemistry- analyze DNA and RNA (most reliable)