Virus and bacteria

Discovery of Viruses : 

Discovery of Viruses Berijerinck (1897) coined the Latin name "virus"  meaning poison for  the substance infecting tobacco plants Wendell Stanley (1935) crystallized sap from tobacco leaves infected with Tobacco Mosaic Virus (TMV) & found virus was made of nucleic acid & protein

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Wendell Stanley Tobacco Leaf with Virus

Viruses : 

Viruses Edward Jenner developed smallpox vaccine using milder cowpox viruses Virology - study of viruses Deadly viruses are said to be virulent Viruses couldn't be seen until electron microscope invented

Viral Characteristics : 

Viral Characteristics Not living organisms Noncellular Consist of a nucleic acid core (DNA or RNA) and a protein coat called the capsid Capsid made of protein subunits called capsomeres Cannot grow or replicate on their own (inactive particles)

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DNA or RNA core capsomeres

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Can only reproduce inside of a living host cell using its raw materials & enzymes Lack ribosomes & enzymes needed for protein synthesis or metabolism Are extremely small particles ranging from 20 - 400 nanometers on average Ebola Virus

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Largest virus is 1000 nanometers in dimension Some can cause disease (smallpox, measles, mononucleosis, influenza colds, AIDS, Ebola) Some may also cause cancers Such as leukemia Virus free cells are rare

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Highly host specific (only infect certain cells) Referred to as phages Viruses are classified into 2 main groups by their nucleic acid --- DNA or RNA Viruses  DNA & RNA viruses are subdivided by capsid shape & whether they do or don't have an envelope

Viral Structure : 

Viral Structure DNA or RNA core surrounded by protein sheath called capsid Nucleocapsid  includes the viral nucleic acid & its capsid Some form lipid rich covering around capsid called the envelope

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Envelope usually formed from host cell membrane Envelope may have spikes to help chemically recognize & attach to the host cell Shaped determined by the arrangement of proteins making up the capsid

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Adenovirus & polio viruses are icosohedral (20 sided) TMV is rod shaped Measles & rabies viruses are helical T -phages have a head & tail Icosohedral Rod Shaped

Bacteriophages or T-Phages : 

Bacteriophages or T-Phages Among the most complex viruses Attack bacterial cells Composed of a icosohedral head, tail, base plate, & tail fibers Long DNA molecule is inside the head  Tail helps inject the viral DNA into host cell Tail fibers used to attach to host

Retroviruses : 

Retroviruses Contain RNA Have an enzyme called reverse transcriptase which helps use the RNA to make DNA Use the host cell's ribosomes & raw materials to make viral proteins Cause some cancers & AIDS

Lytic CycleViral replication that rapidly kills the host cell causing it to lyse or burst : 

Lytic CycleViral replication that rapidly kills the host cell causing it to lyse or burst Adsorption --- phage attaches to cell membrane of host Injection --- nucleic acid (DNA) of virus injected into host cell Replication --- viral DNA inactivates host cell's DNA & uses host's raw materials & ribosomes to make viral DNA, capsids, tails, etc. Assembly --- new viral parts are combined to make new phages Lysis --- enzymes weaken & destroy the cell membrane causing it to lyse releasing new viruses that infect other cells

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The Five stages of the Lytic Cycle

Lysogenic Cycle : 

Lysogenic Cycle Replication in which the virus stays inactive inside of the host cell & doesn't immediately kill it Viruses are called temperate phages Lysogenic steps include adsorption, injection, recombination, cell reproduction, activation, replication, assembly, & lysis Recombination ---Viral DNA joins with host cell DNA forming an inactive prophage

Cont. : 

Cont. Host cell reproduces  normally until activated by an external stimuli  External stimuli unknown, but could be ultraviolet radiation, carcinogens, etc. Once activated, prophage forms new viruses & destroys host cell HIV is an example of a temperate phage

Virus Controls : 

Virus Controls Interferon are proteins made by cells to fight viruses Two types of viral vaccines exist --- inactivated & attenuated Inactivated virus vaccines don't replicate in the host's system Attenuated viral vaccines have been genetically altered so they can't cause disease Antiviral drugs (AZT, acyclovir, & azidothymidine) interfere with viral DNA synthesis Protease Inhibitors interfere with viral capsid production

Bacteria : 

Bacteria Chapter 17

KINGDOMS ARCHAEBACTERIA & EUBACTERIA : 

KINGDOMS ARCHAEBACTERIA & EUBACTERIA

Bacterial Evolution & Classification : 

Bacterial Evolution & Classification Most numerous organisms on earth Earliest life forms (fossils date 2.5 billion years old) Microscopic prokaryotes (no nucleus nor membrane-bound organelles) Contain ribosomes Infoldings of the cell membrane carry on photosynthesis & respiration Surrounded by protective cell wall containing peptidoglycan (protein-carbohydrate) Many are surrounded by a sticky, protective coating of sugars called the capsule or glycocalyx (can attach to other bacteria or host)

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Have only one circular chromosome Have small rings of DNA called plasmids May have short, hairlike projections called pili on cell wall to attach to host or another bacteria when transferring genetic material Most are unicellular Found in most habitats Most bacteria grow best at a pH of 6.5 to 7.0 Main decomposers of dead organisms so recycle nutrients Some bacteria breakdown chemical & oil spills Some cause disease

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Move by flagella, gliding over slime they secrete ( e.g. Myxobacteria) Some can form protective endospores around the DNA when conditions become unfavorable; may stay inactive several years & then re-activate when conditions favorable Classified by their structure, motility (ability to move), molecular composition, & reaction to stains (Gram stain)

Structure of a Bacterium : 

Structure of a Bacterium

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Grouped into 2 kingdoms --- Eubacteria (true bacteria) & Archaebacteria (ancient bacteria) Once grouped together in the kingdom Monera

Kingdom Archaebacteria : 

Kingdom Archaebacteria Found in harsh environments (undersea volcanic vents, acidic hot springs, salty water) Cell walls without peptidoglycan Subdivided into 3 groups based on their habitat --- methanogens, thermoacidophiles, & extreme halophiles

Methanogens : 

Methanogens Live in anaerobic environments (no oxygen) Obtain energy by changing H2 and CO2 gas into methane gas Found in swamps, marshes, sewage treatment plants, digestive tracts of animals Break down cellulose for herbivores (cows) Produce marsh gas or intestinal gas (methane)

Extreme halophiles and Thermoacidophiles : 

Extreme halophiles and Thermoacidophiles Live in very salty water   Found in the Dead Sea, Great Salt Lake, etc. Use salt to help generate ATP (energy) Live in extremely hot (1100C) and acidic (pH 2) water Found in hot springs in Yellowstone National Park, in volcanic vents on land, & in cracks on the ocean floor that leak scalding acidic water

Kingdom Eubacteria (true bacteria) : 

Kingdom Eubacteria (true bacteria) Most bacteria in this kingdom Come in 3 basic shapes --- cocci (spheres), bacilli (rod shaped), spirilla (corkscrew shape) Bacteria can occur in pairs ( diplo- bacilli or cocci)   Bacteria occurring in chains are called strepto- bacilli or cocci Bacteria in grapelike clusters are called staphylococci

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Most are heterotrophic (can’t make their own food) Can be aerobic (require oxygen) or anaerobic (don’t need oxygen) Subdivided into 4 phyla --- Cyanobacteria (blue-green bacteria), Spirochetes, Gram-positive, & Proteobacteria Can be identified by Gram staining (gram positive or gram negative

Gram Staining : 

Gram Staining Developed in 1884 by Danish microbiologist, Hans Gram Bacteria are stained purple with Crystal Violet & iodine; rinsed with alcohol to decolorize; then restained with Safranin (red dye)

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Bacterial cell walls either stain purple or reddish-pink

Gram + Bacteria : 

Gram + Bacteria Thick layer of peptidoglycan (protein-sugar) complex in cell walls & single layer of lipids Stain purple Lactobacilli are used to make yogurt, buttermilk Actinomycetes make antibiotics like tetracycline & streptomycin Disease-causing gram + bacteria produce poisons called toxins Clostridium causes tetanus or lockjaw Streptococcus cause infections such as “strep” throat

Gram - Bacteria : 

Gram - Bacteria Cell walls have a thin layer of peptidoglycan & an extra layer of lipids on the outside Stain pink or reddish  Lipid layer prevents the purple stain & antibiotics from entering (antibiotic resistant) Some are photosynthetic but make sulfur, not oxygen Rhizobacteria grow in root nodules of legumes (soybeans, peanuts…) & fix nitrogen form the air for plants Rickettsiae are parasitic bacteria carried by ticks that cause Rocky Mountain spotted fever Spirochetes can cause syphilis & Lyme disease

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Gram negative Bacteria Gram positive bacteria Strepto and staphylo- Coccus

Phylum Cyanobacteria : 

Phylum Cyanobacteria Gram negative   Carry on photosynthesis & make oxygen Called blue-green bacteria Contain pigments called phycocyanin (red & blue) & chlorophyll a (green)    May be red, yellow, green, brown, black, or blue-green

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First bacteria to re-enter devastated areas Anabaena that live on nitrates & phosphates in water can overpopulate & cause “population blooms” or eutrophication   After eutrophication, the cyanobacteria die, decompose, & use up all the oxygen for fish

Phylum Proteobacteria : 

Phylum Proteobacteria Largest & most diverse bacterial group Subdivided into Enteric bacteria, Chemoautotrophic bacteria, & Nitrogen-fixing bacteria

Enteric bacteria : 

Enteric bacteria Gram negative heterotrophs Can live in aerobic & anaerobic environments Includes E. coli that lives in the intestinal tract making vitamin K & helping break down food Salmonella causes food poisoning

Chemoautotrophs : 

Chemoautotrophs Gram negative bacteria that obtain energy from minerals   Iron-oxidizing bacteria found in freshwater ponds use iron salts for energy

Nitrogen-Fixing bacteria : 

Nitrogen-Fixing bacteria Rhizobium are Gram negative & live in legume root nodules 80% of atmosphere is N2, but plants can’t use nitrogen gas Nitrogen-fixing bacteria change N2 into usable ammonia (NH3) Important part of the Earth’s nitrogen cycle

Methods of Nutrition : 

Methods of Nutrition Saprobes feed on dead organic matter  Parasites feed on a host cell  Photoautotrophs use sunlight for energy, but get carbon from organic compounds (not CO2) to make their own food   Chemoautotrophs obtain food by oxidizing inorganic substances like sulfur, instead of using sunlight

Methods of Respiration : 

Methods of Respiration Obligate aerobic bacteria can’t live without oxygen; (tuberculosis bacteria)  Obligate anaerobes die if oxygen is present; (tetanus bacteria that causes lockjaw) Facultative anaerobes do not need oxygen, but don’t die if oxygen is present; (E. coli) Anaerobes carry on fermentation, while aerobes carry on cellular respiration

Bacterial Reproduction & Genetic Recombination : 

Bacterial Reproduction & Genetic Recombination Most bacteria reproduce asexually by binary fission (chromosome replicates & then the cell divides)     Bacteria replicate (double in number) every 20 minutes under ideal conditions   Bacteria contain much less DNA than eukaryotes

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Bacterial plasmids are used in genetic engineering to carry new genes into other organisms   Bacteria recombine genetic material in 3 ways --- transformation, conjugation, & transduction Binary Fission

Conjugation : 

Conjugation Sexual reproductive method Two bacte   Pili hold the bacteria together   DNA is transferred from one bacteria to the

The End : 

The End