CAMPBELL BIOLOGY IN FOCUS © 2014 Pearson Education, Inc. Urry Cain Wasserman Minorsky Jackson Reece Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge 17 Viruses

© 2014 Pearson Education, Inc. Figure  m

© 2014 Pearson Education, Inc. Concept 17.1: A virus consists of a nucleic acid surrounded by a protein coat  Viruses - a nucleic acid enclosed in a protein coat (capsid )  may contain Double- or single-stranded DNA, or RNA with reverse transcriptase Each virus has a limited host range

© 2014 Pearson Education, Inc. Figure 17.2 RNA Capsomere of capsid Glycoproteins Capsomere Membranous envelope RNA Capsid Head DNA Tail sheath Tail fiber Glycoprotein 80  225 nm 80–200 nm (diameter) 70–90 nm (diameter) 18  250 nm (a) Tobacco mosaic virus 20 nm (b) Adenoviruses 50 nm (c) Influenza viruses 50 nm (d) Bacteriophage T4 50 nm

© 2014 Pearson Education, Inc. Figure 17.3 VIRUS Replication Entry and uncoating DNA Capsid Transcription and manufacture of capsid proteins HOST CELL Viral DNA mRNA Capsid proteins Self-assembly of new virus particles and their exit from the cell

© 2014 Pearson Education, Inc. Replicative Cycles of Phages  two reproductive mechanisms: the lytic cycle and the lysogenic cycle

© 2014 Pearson Education, Inc. The Lytic Cycle  lytic cycle - produces new phages and lyses (breaks open) the host’s cell, releasing new viruses  A phage that reproduces only by the lytic cycle is called a virulent phage Animation: Phage T4 Lytic Cycle

© 2014 Pearson Education, Inc. Figure Attachment 1

© 2014 Pearson Education, Inc. Figure Attachment 1 Entry of phage DNA and degradation of host DNA 2

© 2014 Pearson Education, Inc. Figure Attachment 1 Entry of phage DNA and degradation of host DNA 2 Synthesis of viral genomes and proteins 3

© 2014 Pearson Education, Inc. Figure Attachment 1 Entry of phage DNA and degradation of host DNA 2 Synthesis of viral genomes and proteins 3 Assembly Phage assembly Head Tail Tail fibers 4

© 2014 Pearson Education, Inc. Figure Attachment 1 Entry of phage DNA and degradation of host DNA 2 Synthesis of viral genomes and proteins 3 Assembly Phage assembly Head Tail Tail fibers 4 Release 5

© 2014 Pearson Education, Inc. The Lysogenic Cycle  lysogenic cycle – replicates phage genome without destroying the host  Phages that use both the lytic and lysogenic cycles are called temperate phages  environmental signal can trigger a switch to the lytic mode

© 2014 Pearson Education, Inc. Figure 17.5 The phage injects its DNA. Daughter cell with prophage Many cell divisions create many infected bacteria. Prophage is copied with bacterial chromosome. Phage DNA integrates into bacterial chromosome. Phage DNA and proteins are synthesized and assembled. The cell lyses, releasing phages. Lytic cycleLysogenic cycle Prophage exits chromosome. Phage DNA circularizes. Phage DNA Phage Bacterial chromosome Prophage

© 2014 Pearson Education, Inc. RNA as Viral Genetic Material  Retroviruses use reverse transcriptase to copy their RNA genome into DNA  HIV (human immunodeficiency virus) is the retrovirus that causes AIDS (acquired immunodeficiency syndrome)

© 2014 Pearson Education, Inc. Figure 17.7 Reverse transcriptase HIV Glycoprotein Viral envelope Capsid RNA (two identical strands) HOST CELL Reverse transcriptase Viral RNA RNA-DNA hybrid DNA NUCLEUS Chromosomal DNA RNA genome for the next viral generation mRNA HIV Membrane of white blood cell HIV entering a cell 0.25  m Provirus New virus New HIV leaving a cell

© 2014 Pearson Education, Inc.  Vaccine - a harmless pathogen derivative that stimulates an immune system response

© 2014 Pearson Education, Inc. Figure 17.8 (a) 2009 pandemic H1N1 influenza A virus (b) 2009 pandemic screening 1  m

© 2014 Pearson Education, Inc. Figure 17.UN01