Genetics of Viruses - Introduction to Biology - Lecture Slides, Slides of Biology

Download Genetics of Viruses - Introduction to Biology - Lecture Slides and more Slides Biology in PDF only on Docsity! The Genetics of Viruses and Prokaryotes Docsity.com General Features • acellular • obligate intracellular parasites • cannot reproduce by themselves • no intrinsic metabolism • no ribosomes • typically quite small Docsity.com Describing a Virus • Is the genome DNA or RNA? • Is the nucleic acid single or double stranded? • Is the virion shape simple or complex? • Is the virion surrounded by a membrane? Docsity.com Bacteriophage Infection • viruses that infect bacteria – recognize host using proteins in the capsid – tail assemblies used to inject genetic material through the bacterium’s cell wall Docsity.com Bacteriophage Infection • once injected, the virus may: – reproduce immediately – integrate into the bacterium’s genome, postponing reproduction • two reproductive cycles – lytic – lysogenic Docsity.com Lytic Cycle • late stage – late genes transcribed – code for capsid proteins and proteins to lyse host cell Docsity.com Lysogenic Cycle • infected host harbors virus for generations • termed temperate viruses • prophage integrates into host DNA • can exit and undergo lytic cycle – occurs when cell is damaged or stressed Docsity.com Animal Viruses • may directly infect or be vectored • enter cells in 3 ways – naked virion endocytosed by host cell – enveloped virus endocytosed by host cell – host cell membrane and enveloped virus fuse Docsity.com Prions • molecules of a normal body protein that have changed their three- dimensional configuration • PrPC – The normal protein – is called PrPc (for cellular) – is a glycoprotein normally found at the cell surface inserted in the plasma membrane – has its secondary structure dominated by alpha helices – is easily soluble – is easily digested by proteases – is encoded by a gene designated (in humans) PRNP located on our chromosome 20 Docsity.com Prions • PrPSC • The abnormal, disease-producing protein • is called PrPSC (for scrapie) • has the same amino acid sequence as the normal protein; that is, their primary structures are identical but • its secondary structure is dominated by beta conformation • is insoluble in all but the strongest solvents • is highly resistant to digestion by proteases • When PrPSC comes in contact with PrPC, it converts the PrPC into more of itself (even in the test tube). • These molecules bind to each other forming aggregates • It is not yet clear if these aggregates are themselves the cause of the cell damage or are simply a side effect of the underlying disease process Docsity.com