Unit 12 Viruses & Bacteria
Learning Goals Identify structures and characteristics of Viruses and Bacteria Explain how viruses and bacteria reproduce Recognize the importance of viruses and bacteria Explain how the immune system fights infection
Viruses Infectious particle made of only a strand of DNA or RNA surrounded by a protein coat. Only contains information on how to reproduce the virus Protein coat = capsid Capsid sometimes surrounded by protective lipid envelope
Viruses Smaller than bacteria Non living cannot reproduce on their own Need living cells to help them reproduce
Viruses Structure and shape play an important role in how they work Each type can only infect certain hosts Surface proteins on virus fit to receptor molecules on host cell
Virus Shapes - Polyhedral
Virus Shapes - Helical
Virus Shapes - Enveloped
Viruses that infect bacteria Bacteriophage
Virus Life Cycles Lytic cycle Host cell bursts, releasing new viruses into the host's system, each of which infects another cell
STEP SUMMARY 1. ATTACHMENT - The lytic virus attaches itself to the host cell. 2. ENTRY - The virus injects the nucleic acid into the cell. 3. REPLICATION virus DNA breaks down host DNA and takes over, instructing cell to make virus parts 4. ASSEMBLY Virus parts are put together into new viruses 5. RELEASE - When viruses are mature, they come out of the cell (destroying it) and start to infect other cells.
Virus Life Cycles Lysogenic cycle virus combines its DNA into the host cell's DNA Forms a provirus Virus lays dormant as host cell reproduces (remember mitosis S phase) Trigger can activate the provirus or it can remain a permanent gene
STEP SUMMARY 1. ATTACHMENT The virus attaches itself to the host cell. 2. ENTRY - The virus injects the nucleic acid into the cell. 3. INTEGRATION virus DNA becomes part of host cell's DNA 4. REPLICATION host cell is replicated with viral DNA
Lytic vs. Lysogenic Lytic causes symptoms very quickly New viruses are made and spread to other cells right away Lysogenic organism may have no symptoms for many years Once virus is triggered to enter lytic stage symptoms will develop
Proviruses Activated when lysogenic virus enters a lytic cycle Chicken pox shingles Cold sores
Retroviruses Lysogenic Contain RNA Forces host cell to make viral DNA Viral DNA is added to host cell's DNA
Retroviruses HIV Virus infects white blood cells AIDS: virus enters lytic cycle white blood cells are destroyed body cannot fight off other infections
Prions Infectious particle made only of protein that can cause other proteins to fold incorrectly. Misfolded proteins will not work Can incubate for a long time with no symptoms Once symptoms appear, they worsen quickly and are always fatal Body has no immune response against a protein
Viroids Cause disease in plants Passed through seeds or pollen Single stranded RNA without a protein coat Major economic impact because they can stunt growth in plants
Bacteria and Archaea Most abundant organisms on earth Live in just about every habitat on earth Prokaryotes
Archaea Methanogens Anaerobic Produce methane gas Found in Marshes Bottom of lakes Digestive tracts of herbivores
Archaea Halophiles Anaerobic Live in very salty environments Thermoacidophiles Dead sea, great salt lake Anaerobic Live in hot acidic environments Sulfur springs Ocean vents
Bacteria Heterotrophs Parasitic feed on living organisms Saprophytic feed on dead organisms/waste
Bacteria Autotrophs Cyanobacteria photosynthesizer Usually blue green Live in ponds, streams, or other moist areas Chains of independent cells Probably earth's 1 st oxygen producers Chemosynthesizers energy comes from break down of inorganic compounds Convert atmospheric nitrogen to usable compounds (nitrogen fixation)
Bacteria Structure
Identifying Bacteria 2 groups based on amount of peptidoglycan in cell wall Gram negative thin layer, stain red Gram positive thick layer, stain purple
Identifying Bacteria Further classified by shape Spherical (cocci) Rod (basilli) Spiral (spirilla) Comma (vibrios) Corkscrew (spirochates)
Reproduction Binary fission asexual Bacteria cell copies its DNA Both copes of DNA attaches to plasma membrane Partition forms to create 2 identical new cells Takes less than 20 minutes under ideal conditions
Reproduction Conjugation Sexual One bacterium transfers part of its chromosome across a pilus Offspring not genetically identical to parent
Bacterial Survival Endospore specialized cell with thick, protective wall Helps cell survive harsh conditions Can be killed by heating over 100 degrees Celsius
Importance of Bacteria Nitrogen fixation Digestive tract (probiotics) Fermenation (cheese, yogurt, pickles) Bioremediation (breaks down pollutants)