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Why is it advantageous for viruses to possess different shapes? RNA DNA Capsomere Membranous envelope RNA Head DNA Capsid Capsomere of capsid Glycoproteins Glycoprotein 18 250 nm 70–90 nm (diameter) 80–200 nm (diameter) 20 nm (a) Tobacco mosaic virus 50 nm (b) Adenoviruses 50 nm (c) Influenza viruses True or False. Bacteria have the ability to infect viruses. Tail sheath Tail fiber 80 225 nm 50 nm (d) Bacteriophage T4 Obligate intracellular parasite life cycle VIRUS 1 Entry and DNA uncoating Capsid 3 Transcription and manufacture of capsid proteins 2 Replication HOST CELL Viral DNA How do viruses identify their host cells? mRNA Viral DNA Many viruses are species specific and most will target one type of cell Capsid proteins 4 Self-assembly of new virus particles and their exit from the cell What are the advantages and disadvantages of each cycle? What does lysogenic mean? Phage DNA Daughter cell with prophage The phage injects its DNA. Cell divisions produce population of bacteria infected with the prophage. Phage DNA circularizes. Phage Bacterial chromosome Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Lytic cycle Lysogenic cycle The bacterium reproduces, copying the prophage and transmitting it to daughter cells. The cell lyses, releasing phages. Lytic cycle is induced or Lysogenic cycle is entered New phage DNA and proteins are synthesized and assembled into phages. Temperate phage = λ phage that is used for research Why might humans utilize this type of phage? Prophage Phage DNA integrates into the bacterial chromosome, becoming a prophage. What are some harmful examples of a bacteria containing prophages? Phage DNA The phage attaches to a host cell and injects its DNA Bacterial chromosome Lytic cycle • Virulent or temperate phage • Destruction of host DNA • Production of new phages • Lysis of host cell causes release of progeny phages Prophage Lysogenic cycle • Temperate phage only • Genome integrates into bacterial chromosome as prophage, which (1) is replicated and passed on to daughter cells and (2) can be induced to leave the chromosome and initiate a lytic cycle Capsid and viral genome enter the cell Capsid The host cell digests the capsid releasing RNA into the host cell RNA HOST CELL Envelope (with glycoproteins) Viral genome (RNA) Template There are single stranded and double stranded viruses containing either DNA or RNA mRNA Capsid proteins ER Glycoproteins Copy of genome (RNA) RNA viruses have higher mutation rates because they lack replication error checking New virus Viral envelope Glycoprotein Capsid Reverse transcriptase HIV RNA (two identical strands) HIV How is this different from the previous slide? Membrane of white blood cell Why is HIV called a retrovirus? HOST CELL Reverse transcriptase Viral RNA RNA-DNA hybrid 0.25 µm DNA HIV entering a cell NUCLEUS Provirus Chromosomal DNA RNA genome for the next viral generation New virus New HIV leaving a cell mRNA Which cells are targeted by HIV? Viral Phylogenetics Fimbriae Cell wall Why are bacteria so successful? Circular chromosome Capsule Sex pilus What is the role of each of these components? Internal organization Flagella True or False. Bacteria are unable to create proteins. Gram staining is used to determine which type of cell wall is present in the bacteria What are the major differences? Carbohydrate portion of lipopolysaccharide Cell wall Peptidoglycan Cell wall layer Outer membrane Peptidoglycan layer Plasma membrane Plasma membrane Protein Protein Grampositive bacteria (a) Gram-positive: peptidoglycan traps crystal violet. Staphylococcus aureus,, Streptococcus pneumoniae Gramnegative bacteria 20 µm (b) Gram-negative: crystal violet is easily rinsed away, revealing red dye. Eschericiacoli, Klebsiella pneumoniae, Neiserria gonorrhea, Vibrio cholera Phage DNA Transduction A+ B+ A+ A bacteria is infected with bacteriophage DNA B+ Donor cell The virus undergoes either the lytic cycle or the lysogenic cycle A+ Recombination A+ A– B– Recipient cell A+ B– Recombinant cell If bacteria acquires DNA from its environment (i.e. not from a virus) it changes its genome through transformation Plasmids – extracellular chromosomes that can give bacteria new traits F plasmid F factor is present in the F plasmid to form the sex pilus Bacterial chromosome F+ cell F+ cell Mating bridge F– cell F+ cell Bacterial chromosome (a) Conjugation and transfer of an F plasmid Hfr cell A+ A+ F factor F– cell A+ A+ A– Recombinant F– bacterium A– A– A+ A– (b) Conjugation and transfer of part of an Hfr bacterial chromosome R plasmid – provides resistance to certain antibiotics How does conjugation differ from transformation or transduction? A+ Uptake of K by plants (mg) 1.0 0.8 0.6 0.4 0.2 0 No Strain 1 Strain 2 bacteria Soil treatment Strain 3 Euryarchaeotes Crenarchaeotes UNIVERSAL ANCESTOR Domain Archaea Korarcheotes Domain Eukarya Eukaryotes Nanoarchaeotes Proteobacteria Spirochetes Cyanobacteria Gram-positive bacteria Domain Bacteria Chlamydias Halophiles, thermophiles, and methanogens belong to which Domain? What is a facultative anaerobe? True or False. All bacteria is harmful.
