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Chapter 20 Viruses, Bacteria, and Archaea Viruses, Viroids, and Prions 20.1 Virus • Non-cellular parasitic agent consisting of an outer capsid and inner core of nucleic acid. • 2500 species identified • Have some characteristics of living organisms • DNA or RNA • Evolve and Replicate • BUT can only replicate using host cells machinery • No metabolism • Do not respond to stimuli • Do not fossilize Structure of Virus • Categorized by: 1. Size and shape (thread-like or polyhedral) 2. Type of nucleic acid and single or double stranded 3. Presence or absence of outer envelope • ALL have capsid and inner core (DNA or RNA) • Range from 3-100 genes • IF capsid is outermost structure- NAKED VIRUS • IF surrounded by outer membranous envelope- ENVELOPED VIRUS Parasitic Nature • Cannot replicate outside living cell • BUT has genetic material • Must infect living cell SO: Virus “hijacks” cells protein synthesis machinery to replicate the nucleic acid and other parts of the virus *Some infected cells are killed or damaged by virus Ex: Pneumonia or bronchitis Host Specificity • Particular virus is only capable of reproducing in a specific organism • rabies-animals • Can even be tissue specific • Hepatitis-liver • HIV- certain blood cells • Determined by structure (naked or spiked envelope) • Lock and key manner with host surface • Some medicines mess w this manner to prevent further infection Reproduction of Viruses 1. Attachment- virus surface molecules and host cell receptors 2. Penetration- Host cell engulfs virus OR Virus injects genome 3. Biosynthesis- viral components synthesized using hosts stuff 4. Maturation- assembled into new viruses 5. Release- new virus exits though lysis or budding in order to infect new host cells Reproduction of Bacteriophages • Bacteriophages- viruses that parasite bacteria • Lytic- 5 steps occur immediately, cell lysed and the end by lysozyme • Bacterial cell dies, 100s of new viruses released • Lysogenic- not immediate, latent (not actively replicating) • Attachment • Penetration Integration • Then, biosynthesis, maturation, release • Integration- viral DNA becomes incorporated in Bacterial DNA Reproduction of Bacteriophages • Lysogenic cells- carry copy of genome in the future induce into lytic cycle by environmental factors • EX: bacteria that causes strep throat is carrying prophage, then it becomes scarlet fever Reproduction of Animal Viruses • Introduce genetic material differently • Some envelope viruses- attach, fusion of spikedenvelope • Many naked and other enveloped viruses- endocytosis • Enters, uncoated, then lytic or lysogenic cycle happens • Some viruses enter directly into lytic cycle causing rapid and severe destruction of host cells. • HIV, however, enters lysogenic and is inactive for many years before AIDS symptoms show up. Reproduction of Animal Viruses • Viral Release• some release by budding, picks up its envelope from plasma membrane • Naked viruses released by lysis of host cell Retroviruses • Animal viruses with RNA genomes that have to be converted to DNA within host cell by an enzyme called reverse transcriptase • Before it can integrate into host genome, RNA DNA RNA cDNA DNA Retroviruses • AIDs delayed by treatment with antiretroviral drugs • AZT- reverse transcriptase inhibitors • Acyclovior- inhibits replication of HIV viral DNA Emerging Viruses • Use to not be a problem, • AIDs, West Nile, HPS, SARS, Bird Flu, • Important to get flu shot every year. • HIV also rapidly emerging. That’s why we cant find a cure Viroids • 1000 different viruses cause disease in plants • 12 not viruses but viroids (naked strand of RNA) Prions • Proteins that normally exist in an animal but have different conformation or structures • Fatal brain disease • TSEs are neurodegenerative diseases that destroy nerve tissue in brain • Untreatable and fatal • Mad cow disease (bovine spongiform encephalopathy) (BSE) Prokaryotes 20.2 Prokaryotes • Includes bacteria and archaea, which are fully functioning, living, singlecelled organisms. • Today, we know that bacteria are plentiful in air, water, and soil. Structure of Prokaryotes • Surrounded by plasma membrane and a cell wall situated outside the membrane. • Cell wall prevents cell from bursting or collapsing • Some have additional cover layer of polysaccharides called a glycocalyx • Well organized- capsule • Loosely organized- slime layer Structure of Prokaryotes • Some move by means of a flagella • Filament is inserted into a hook anchored by a basal body. • 360- degree rotation Structure of Prokaryotes • Many adhere to surfaces by means of fimbriae • Short, bristle-like fibers extending from the surface. • Ex: Neisseria gonorrhoeae attach to host cell and cause gonorrhea, and STD Structure of Prokaryotes • Do not have a nucleus • Do have a nucleoid region where single chromosome where DNA is found. • Also have plasmids (rings of DNA)- genes for antibiotic resistance, production of toxins, and degradation of chemicals. Reproduction of Prokaryotes • Mitosis- formation of spindle apparatus, does NOT occur in prokaryotes. • Reproduce asexually by binary fission. • Single circular chromosome replicates, then two copies separate as cell enlarges eventually leading to two cells. • Takes about 12 minutes Reproduction of Prokaryotes In eukaryotes, genetic recombination occurs as a result of sexual reproduction. Prokaryotic gene recombination: 1. Conjugation- two bacteria are temp. linked together and pass DNA. 2. Transformation- cell picks up free pieces of DNA secreted by others or released by dead cells. 3. Transduction- bacteriophages carry portions of DNA form one to the other. Exit Slip 1. Explain the difference between a eukaryote nucleus and a prokaryote nucleoid. 2. Explain 3 ways how prokaryotes can recombine their DNA without sexual reproduction. Bacteria 20.3 Characteristics • Most protected by cell wall composed of peptidoglycan 1. Gram-positive- thick peptidoglycan cell wall 2. Gram-negative- thin peptidoglycan and second plasma membrane, often blocks antibiotics Gram Stain Shapes • Spirilli • Cocci • bacilli Growth Arrangement • Staph- clusters • Strept- chains • Diplo- pairs Metabolism • Aerobic- requires oxygen to grow. • Facultative anaerobes- can grow in both. • Obligate anaerobes- cannot grow in oxygen. • Ex: botulism, tetanus • Intestines or deep puncture wounds Autotrophic Bacteria Photoautotrophs- photosynthetic, use solar energy to reduce CO2 to organic compounds 2 types: 1) anoxygenic photosynthesis- does not produce oxygen Ex: green sulfur bacteria 2) oxygenic photosynthesis- produces oxygen Ex: cyanobacteria Autotrophic Bacteria Chemoautotrophs- chemosynthetic, oxidize inorganic compounds such as hydrogen gas, hydrogen sulfide, and ammonia to reduce CO2 to organic compounds. Heterotrophic Bacteria Chemoheterotrophs- obtain carbon and energy in the form of organic nutrients others produced. Ex: feed on tissues and fluids of living host • One type called saprotrophs serve as decomposers that break down organic matter from dead organisms. Chemoheterotrophs are used to make acetones, butter, cheese, silk, coffee and some antibiotics. Symbiotic Relationships • 2 different species living together, 3 types 1. Mutualism- both benefit • Live in intestines and release K and B12 2. Commensalism- one benefits, other is unaffected • One usually modifies environment so other benefits • Obligate anaerobes live in intestines only because E. coli uses up oxygen Symbiotic Relationships 3. Parasitism- one benefits, harming the other • Pathogens • They aren’t actually doing the harming, the toxins they release are • Ex: tetanus- releases toxin that travels throughout body Symbiotic Relationships • Endospores- dried seed, deadliest pathogens produce these • Some of the cytoplasm and copy of chromosome becomes dehydrated • Can survive harsh environments, deserts, boiling temp., extreme UV rays, and can survive for long periods of time. • Anthrax endospores from 1,300 years ago can still cause serious infection • Botulism from canned food • Not means of reproduction but survival. Antibiotics • 2 classes: 1. Inhibit protein synthesis • Erythromycin and tetracyclines affect ribosomes 2. Inhibit cell wall biosynthesis • Penicillin, ampicillin Antibiotics • Heavily prescribed to treat infection, OFTEN when not needed. • Bacteria is becoming increasingly resistant to antibiotics • WHY? • They can even pass resistance to others by conjugation, transformation, and transduction • Ex: staphylococcus aureus was only 3% resistant to penicillin when it came out. Now its over 90% resistant. Cyanobacteria • Gram- negative with unusual traits. • Photosynthesize • “blue-green algae” • Now we know it is not an algae but a prokaryote • Mask color of chlorophyll with other pigments to make it different colors. • No means of locomotion How can something survive if it cannot move? Cyanobacteria • Can photosynthesize and fix atmospheric N2 so no need to move for food. • Can serve as food for some heterotrophs • fresh and marine waters, soils, moist surfaces, hot springs, harsh environments • If care is not taken when disposing of wastes, phosphates build up and drain into lakes and ponds, resulting in a “bloom” of this organism. • Light cannot penetrate to lower levels • When cyanobacteria dies, the decomposer uses up all oxygen, killing the fish