Chapter 18 Viruses and Bacteria

18.1 Viruses

What is a Virus? Non-living particles - don’t exhibit all the criteria for life Can replicate only inside another cell - host cell Named after disease they cause –Hepatitis A Virus –Measles Virus Can infect bacteria  Bacteriophage Viruses are species specific

Viral Structure Inner core of nucleic acid (RNA or DNA) Outer protein coat called a capsid

Attachment to a host cell Virus recognizes a specific site, receptor site, on a host cell A protein on the virus fits into a receptor site Proteins are shape specific – not the right shape it won’t fit

Viral Replication Cycle (Lytic Cycle) –Virus attaches and incorporates its DNA into host cell one of two ways –Inject its nucleic acid –Fuses with cell creating a vacuole inside the host cell –Virus takes over host cell’s genetic material –Host cell makes new virus –New virus kills host cell –Takes about 30 minutes

Lysogenic Cycle Starts the same as lytic cycle; however, instead of taking over genetic material, the viral DNA is integrated into host cell’s chromosome  provirus A provirus may not affect the functioning of its host cell; however, every time host cell replicates, the provirus is replicated as well

Every cell that originates from an infected host has a copy of the provirus The lysogenic cycle can continue for many years, but at any time the provirus can be activated and enter a lytic cycle, killing the host cell No known factors that activate a provirus, but scientists believe that stress may play a role

Disease symptoms of provirus Lysogenic process explains reoccurrence of cold sores –When the provirus enters a lytic cycle a cold sore erupts Many disease-causing viruses have lysogenic cycles –Herpes simplex I –Herpes simplex II –Hepatitis B –Chicken pox  later in life this provirus enters the lytic cycle and appears as shingles

Retrovirus RNA virus Once inside the cell the retrovirus makes DNA from its RNA using an enzyme called reverse transcriptase The viral DNA is integrated into the host cell’s chromosome and becomes a provirus If reverse transcriptase is found in an individual, it is evidence of an infection by a retrovirus

HIV: WBC infection HIV infects the white blood cells Newly made viruses are released by exocytosis and promptly infect other WBC’s Infected host cells function normally because HIV is a provirus HIV patients will gradually lose WBC’s and develop AIDS

Plant Viruses 1 st virus to be identified  tobacco mosaic virus (causes disease in tobacco plants) There are 400 known plant viruses that cause as many as 1,000 plant diseases Some viruses are not harmful –Tulip breaking virus  causes beautiful patterns in flowers

18.2 Archaebacteria & Eubacteria

Diversity of Prokaryotes Unicellular organisms that do not have membrane-bound organelles Classified into two kingdoms –Archaebacteria (three types) –Eubacteria

Archaebacteria Type 1 - Mesophiles Anaerobic, methane producing bacteria Live in marshlands, digestive tracts of animals

Archaebacteria Type 2 - Halophiles Live anywhere with a concentration of salt that is 5X higher than the salt concentration of the ocean –Dead Sea –Great Salt Lake (Utah)

Archaebacteria Type 3 - Thermophiles Lives in very hot temperatures –Yellowstone National Park –Deep sea hydrothermal vents Contain enzymes that can function at high temperatures (  113  C)

Eubacteria: The Heterotroph Live almost anywhere and use organic molecules as a food source Some are parasites Some are saprophytes, organisms that feed on dead organisms or organic wastes

Eubacteria: Photosynthetic autotrophs Live in sunlight because they need light to make the organic molecules that are their food Cyanobacteria – contain chlorophyll, live in ponds, streams, and moist areas of land and are composed of chains of independent cells

Eubacteria: Chemosynthetic Autotrophs Break down and release energy from inorganic compounds containing sulfur and nitrogen Do not need sunlight Convert atmospheric nitrogen into the nitrogen-containing compounds that plants need

What is a Bacterium? Typical Bacterial Cell –Chromosome – single circular – contains most genes –Cell wall –Capsule that surrounds the cell wall –Plasma Membrane –Pilus – helps bacteria stick to cell walls –Plasmid – small circular chromosome – contains genes – 1 or more in cell –Flagellum

Penicillium notatum Penicillin – discovered in 1928 by Alexander Fleming First antibiotic used in humans Interferes with cell wall construction Approximately 10% of Americans are allergic Causes approximately 300 deaths per year in United States

Identifying Bacteria Gram stain – distinguishes two groups of bacteria – they react to antibiotics differently –Gram positive - purple –Gram negative – pink Three common shapes –Bacillus = Rod shaped –Coccus = Sphere shaped –Spirillum = Spiral shaped

Bacteria grows in characteristic patterns –Diplo = paired arrangement of cell growth –Staphylo = arrangement where cells resemble grapes –Strepto = arranged in chains of cells

Reproduction by binary fission Produce asexually via Binary Fission –1 st copies its chromosome –2 nd Attaches to cell membrane –3 rd Partition forms between chromosomes and it separates the two cells Reproduction can be very rapid = some can reproduce every 20 minutes

Sexual Reproduction Some bacteria reproduce via conjugation –One bacterium transfers all or part of its chromosome to another cell through the pilus that connects the two cells Results in new genetic composition This new cell can then undergo binary fission

Adaptations in bacteria Obligate aerobes – require oxygen to live – Mycobacterium tuberculosis causes TB Obligate anaerobes – killed by oxygen – Treponema pallidum causes syphilis

Endospore – bacterium’s DNA and cytoplasm encased by a tough outer covering –Resists temperature extremes – can survive in 100  C = 212  F –Does not dry out –Resists harsh chemicals Bacterium rests and does not reproduce until conditions are favorable

Clostridium botulinum –obligate anaerobe that produces endospores –Releases toxins, deadly poisons, that saturate canned food –Causes botulism

Clostridium tetani –Obligate anaerobe that produces endospores –Exists almost everywhere; enter through a wound –Produces nerve toxin –Causes tetanus

Nitrogen Fixation Bacteria change N 2 (nitrogen gas) into NH 3 (ammonia) = nitrogen fixation Other bacteria then convert NH 3 into NO 2 - (nitrite) and NO 3 - (nitrate) – plants use these Bacteria are the only organisms that can perform these chemical changes

Recycling of nutrients Decomposing bacteria break down organic materials in dead organisms releasing the nutrients to the environment feeding plants and algae

Food & Medicine Bacteria is used to make foods –Yogurt - Streptoccus thermophilus and Lactobacillus –Swiss cheese – above two, as well as, Propionibacter –Vinegar - Acetobacter aceti Bacteria used to make antibiotics –Streptomycin – 1 st remedy for TB –Erythromycin – respiratory tract infections –Bacitracin – topical antibiotic –Neomycin – topical/oral antibiotic

Bacteria cause disease Cause approximately ½ of the human diseases Enter through openings Carried by air, food, and water –Strep throat –Cholera –Lyme disease

THE END