MCB 100 1st Edition Lecture 38 Outline of Last Lecture I. Topical fungal infections II. Fungal infections of the lungsIII. Protozoa IV. Examples of protozoa Outline of Current Lecture I. Properties of virusesII. BacteriophageIII. Human and animal virusesCurrent LectureI. Viruses- Propertiesa. Cannot reproduce unless they are inside a suitable host cell: i. Suitable host cell must have a receptor that the virus can attach to so it can enter the cellii. A suitable host cell must also have all of the enzyme that the virus needs for replicating it's genetic material and making viral proteins b. Viruses are very specific in their host rangec. Every type of cellular organism can be infected by some type of virus, but a given virus will infect only specific hosts d. Viruses always have a limited host rangee. Viruses that infect plants don’t bother animals f. Viruses that infect bacteria (bacteriophages) don’t invade eukaryotic cells g. Viruses are much smaller than bacteria or protozoa h. Virus capsids often, but not always, have an icosahedral shape- a 20-sided figure with each side being an equilateral triangle i. Capsid of polio virus consists of 60 molecules of coat protein, each face is madeof 3 b. Some viruses have an envelope that covers the capsid, some don't i. Viral envelope is a lipid bilayer with embedded proteins but it is not an active cytoplasmic membrane b. Viruses do not absorb nutrients or excrete wastes when they are outside a host cellc. Viruses that are outside host cells have no metabolism and can't repair themselves if they are damaged d. Naked viruses:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.i. Polio virusii. Rhino virusb. Enveloped viruses:i. HIVii. Influenzaiii. Yellow fevera. Tobacco mosaic virusi. Causes a disease in plants ii. Helical RNA virus iii. Coat proteins cover the genomic RNA II. Bacteriophagea. Virus that attacks a bacterial host b. Phage kills bacteria, creating a hole in the lawn of bacterial cells (plaque)c. "phago" = to eat or swallowd. Bacterial viruses are called phages because it looks like something is eating the bacteria making plaques e. Bacteriophage T4 attacks Escherichia coli i. When T4 reproduces, the progeny phage particles exit the old host cell by causing the cell to lyse (break open)- "lytic cycle" of replicationb. Bacteriophage lambda can reproduce and kill E. coli (lytic cycle) or can become dormant within the host cell (lysogeny)i. Life cycle of bacteriophage lambda:1. Attachment2. Entry3. Lytic cycle: virus actively grows and kill the cell when progeny viruses break out a. Synthesisb. Assembly c. Release2. Lysogenic cycle: virus remains dormant and host cell continues to grow and dividea. Integration of phage DNAb. Host cell divides2. Lysogeny vs. lytic cycle- how is the decision made?a. When the lambda DNA first gets into an E. coli cell, both regulatory factors that are required to activate transcription of phage genes and the lambda repressor protein are madeb. It’s a race to see if the phage DNA is first repressed and enters the lysogenic cycle or is actively transcribed so it enters the lytic cyclec. When a lambda lysogen encounters harsh conditions, the lambda repressor protein may be degraded--> this causes activation of the prophage genesd. Viral DNA is excised from the host chromosome and lambda enters lytic cycleIII. Human and animal virusesa. Some human viruses are always in a lytic cycle- these viruses kill human cells i. Examples:1. Rhinoviruses: small RNA viruses that cause common cold 2. Enteroviruses: small RNA viruses that cause viral diarrhea3. Hepatitis A: RNA virus that attacks liver cells4. Hemorrhagic fever viruses- Yellow Fever and Ebola virus b. Some viruses may become latent (dormant) within human cells- these viruses have astage in their life cycle that includes a DNA copy of their genome- they may disrupt regulation of cell division and possibly cause canceri. Examples:1. Retroviruses: RNA viruses that replicate via DNA intermediates Human Immunodeficiency Virus (HIV)2. Some DNA viruses: Herpes viruses, Chickenpox, Hepatitis B b. Some animal viruses exit host cell by budding- unlike lysis, budding doesn't kill host cell- viral envelope is derived from the cytoplasmic membrane of the old host cell, with some viral proteins embedded within it- viral glycoproteins mark an infected cell with foreign antigens c. Some animal viruses exit host cell by lysis- these generally don’t have an
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