Chapter 27 Viruses Joe Ganoe Jesus Trochez

Types of Viruses Plant Virus – Helical capsid shape Animal Virus – Icosahedral capsid Bacterial Virus – Icosahedral head : helical tail Animal Virus – Helical capsid within envelope

Lytic Cycle Reproductive virus cycle 5 step process Attachment Penetration Synthesis Assembly Release

Lytic Cycle Steps Attachment – Virus attaches to cell wall Penetration – Viral DNA injected into cell Synthesis – Protein and nucleic acid form Assembly – Involves spontaneous assembly of capsid and enzyme to insert DNA Release – Lysis (disintegration of cell by rupture of its plasma membrane) of cell

Lysogenic Cycle 3 Step process – Intergration – Propagation – Induction Starts at the 2 nd cycle of the Lytic Cycle (Penetration) After it ends the virus returns to Synthesis in the Lytic Cycle This cycle does not immediately kill the cells they infect, but use the cell to make it into another virus cell

Lysogenic cycle Integration – Integration of genome leads to prophage Propagation – Propagation of prophage along with host genome Induction – Induction prophage exits the bacterial chromosome, viral genes are expressed

Key Terms Lytic cycle – A viral cycle in which the host cell is killed (lyse) by the virus after viral duplication to release viral particles Lysogenic Cycle – A viral cycle in which the viral DNA becomes integrated into the host chromosome and it replicated during cell reproduction. Results in vertical rather than horizontal transmission Bacteriophage – A virus that infects bacterial cells – Also called a phage Capsid – The outermost protein covering a virus Tissue Tropism – The affinity of a virus fro certain cells with a multicellular host – For example, hepatitis B virus targets liver cells. Host range – that can be infected by a particular virus Icosahedron – A structure consisting of 20 equilateral triangular facets – This is commonly seen in viruses and forms one kind of viral capsid Phage conversion – The range of organismsthe phenomenon by which DNA forma virus, incorporated into a host cell’s genome, alters the host cell’s function in a significant way Envelope – A casing that protects the virus from being attacked. Only found in animal cells.