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Viruses and Bacteria Chapter 17 & 24
Chapter 17 & 24
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Evolution Connection https://www.youtube.com/watch?v=yybsSqcB7mE
Requirements for Evolution: Variation Organisms must be different, this allows for different survival abilities in different environments Reproduction Genes must be passed to the next generation Environmental Pressures The Environment puts pressure on organisms The organisms with the most favorable traits go on to live and reproduce.
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Overview Comparison Viruses Eukaryotes Prokaryotes Not cells
Plant or Animal Cells Sometimes plasmids (extra DNA circular) Nucleus DNA – Iinear chromosomes Cell Membrane (and cell wall in plants) Large Ribosomes Energy in Mitochondria Complex Archaea or Bacteria Cells Plasmids No Nucleus – nucleiod region DNA – circular Chromosomes Cell Membrane and Cell Wall Small Ribsomes Energy in Cell Membrane Simple Not cells No Nucleus or nucleoid DNA or RNA Protein Coat – Capsid No Ribosomes No Energy – Host cell Simplest
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Cellular Structure of Bacteria and Archeae
DNA (nucleoid region) & Ribosome in cytoplasm Cell wall in most, capsule in some Archea: * no nucleus * no membrane bound organelles * Sometimes introns (pieces of DNA that are cut out) * no histones (proteins that help coil DNA) * circular chromosomes
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Genetic Recombination in Prokaryotes
Binary Fission: asexual, rapid division (20 min. ish), faster evolutionary process Transduction: phages (viruses that infect bacteria) transfer genetic material from one bacterial cell to another Conjugation: Exchange genetic material in “good environmental conditions” Use sex pili to pull together, 1 way exchange F plasmid: allow mating bridge, fertility R plasmid: Allow antibiotic resistance
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Viral Structure Infectious (parasitic) particles with nucleic acids enclosed in a protein coat. Nucleic Acids – DNA or RNA Double stranded DNA Single stranded DNA Double stranded RNA Single stranded RNA
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Viral Structure Capsid – protein coat covering - capsomeres
Rod shaped Polyhedral complex Envelope – surrounds the capsid of some viruses Host cell phospholipids and proteins Glycoprotein spikes Tail – found on bacteriophages Viruses that infect bacteria as the host
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Viruses & the Host Cell Each type of virus can only infect a certain range of host cells – host range Use “lock and key” fit between host cell receptors and virus Have no correction mechanism, more mutations!! Host cell provides the “machinery” to reproduce the viral genome tRNA Ribosomes amino acids Polymerases ATP Virus hijacks the host cell parasite
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VIRUS Capsid proteins mRNA Viral DNA HOST CELL DNA Capsid Figure 18.5
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Viral - Bacteriophage Reproduction 19_06LysogenicLyticCycles_A.swf
Virus kills the host cell Uses it to reproduce then lyses (blows up) the cell releasing new viruses to infect new host cells Virulent phages (bacteriophages) Lysogenic Cycle Virus reproduces its genome without destroying the host cell “Dormant cycle” Temperate phages use both lytic and lysogenic
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Phage assembly Head Tails Tail fibers Figure 18.6
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Many cell divisions produce a large population of bacteria infected with the prophage.
The bacterium reproduces normally, copying the prophage and transmitting it to daughter cells. Phage DNA integrates into the bacterial chromosome, becoming a prophage. New phage DNA and proteins are synthesized and assembled into phages. Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Certain factors determine whether The phage attaches to a host cell and injects its DNA. Phage DNA circularizes The cell lyses, releasing phages. Lytic cycle is induced Lysogenic cycle is entered or Prophage Bacterial chromosome Phage DNA Figure 18.7
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Animal Enveloped Viruses
RNA Capsid Envelope (with glycoproteins) HOST CELL Viral genome (RNA) Template proteins Glyco- mRNA Copy of genome (RNA) ER Figure 18.8 Glycoproteins fuse with receptors on host cell membrane Capsid enters host cell Viral genome replicates New virus leaves the host cell through the cell membrane
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Retroviruses RNA virus that uses reverse transcriptase to create DNA
Figure 18.9 Reverse transcriptase Viral envelope Capsid Glycoprotein RNA (two identical strands) Retroviruses RNA virus that uses reverse transcriptase to create DNA DNA is then incorporated into the cells chromosome and transcribed and translated with the rest of the cells genes. Provirus – becomes a permanent part of the cells DNA HIV 19_08HIVReproCycle_A.swf
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Figure 18.10 mRNA RNA genome for the next viral generation Viral RNA RNA-DNA hybrid DNA Chromosomal DNA NUCLEUS Provirus HOST CELL Reverse transcriptase New HIV leaving a cell HIV entering a cell 0.25 µm HIV Membrane of white blood cell The virus fuses with the cell’s plasma membrane. The capsid proteins are removed, releasing the viral proteins and RNA. 1 Reverse transcriptase catalyzes the synthesis of a DNA strand complementary to the viral RNA. 2 catalyzes the synthesis of a second DNA strand complementary to the first. 3 The double-stranded DNA is incorporated as a provirus into the cell’s DNA. 4 Proviral genes are transcribed into RNA molecules, which serve as genomes for the next viral generation and as mRNAs for translation into viral proteins. 5 The viral proteins include capsid proteins and reverse transcriptase (made in the cytosol) and envelope glycoproteins (made in the ER). 6 Vesicles transport the glycoproteins from the ER to the cell’s plasma membrane. 7 Capsids are assembled around viral genomes and reverse transcriptase molecules. 8 New viruses bud off from the host cell. 9
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Viral Treatments None Prevention – vaccines
Antibiotics only work against bacteria Prevention – vaccines Weak or “dead” viruses that trigger an immune response so the body can fight the real thing.
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Plant Viruses Figure 18.12 Horizontal transmission – virus enters the plant through a damaged cell wall Vertical transmission – virus passed from the parent to offspring
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Simplest Pathogens Viroid – not true viruses
circular RNA that infects plants Smaller than viruses Prion – infectious protein Cause degenerative diseases in animals Virtually indestructable – not killed in cooking process Mad cow disease Figure 18.13 Prion Normal protein Original prion New prion Many prions
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Emerging Viruses Map of Novel emerging viruses from 1980 to 2007
How do they get here? Mutation of existing viruses High Mutation rate Movement from small areas HIV Other animals Bird Flu
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