Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Effects of viral infection may be mild or severe The symptoms of a viral infection vary depending on the host cell that is destroyed. Cell death also triggers immune response which can cause fevers and inflammation. B. Some animal viruses linger for years. When virus does not produce symptoms, but the viral genetic information is still inside the cell it if called a latent viral infection. Examples: herpes simplex 1 and HIV Some can cause cancer like HPV and EpsteinBarr Antiviral medications can interfere with enzymes that are unique to viruses, but few drugs can kill viruses without killing host cells. The high rate of mutation in viruses make them unlikely to be curable. Vaccines train the immune system to recognize viruses and combat them before infection occurs. Smallpox and polio have nearly been eradicated. Plant viruses like the tobacco mosaic virus cause spots or streaks in plant tissue. Plants can fight off viral infections using posttranscriptional gene splicing. Viral mRNA is degraded which prevents new viruses from forming. A. a viroid is an infectious RNA molecule Viroids are naked RNA that can infect a cell. They cannot encode proteins, but they can cause serious diseases in crop plants and are spread by wind, insects, and farm equipment. B. A prion is an infectious protein A prion is a “proteinaceous infectious particle” . Prions cause mad cow disease and Creutzfeldt-Jakob disease. 16.1 prokaryotes are a biological success story Prokaryotes are single-celled that lacks a nucleus and membrane bound organelles. 2 domains- Bacteria and Archaea Prokaryotes live everywhere on earth. There are many species and more are being discovered. Microbiologists learn from cultured cells and from extracting microbial DNA directly from the environment. A. Microscopes reveal cell structures Internal structures- cell membrane, DNA(a circular chromosome), ribosomes. The nucleoid is the region where the DNA is located. There is NO nuclear membrane. Many also have a plasmid which is a circle of DNA apart from the chromosome. Plasmids are used in genetic engineering. External structures- Cell wall(most bacteria and archaea) that is made of peptidoglycan a polysaccharide. Coccus- spheres Bacillus-rods Spirillum- spiral or corkscrew Arrangements- clusters(staphylo), chains(strepto) Gram stain reaction distinguishes between two types of cell walls Gram-positive- thicker cell walls made of peptidoglycan that stain purple Gram-negative- thinner cell walls that stain pink. Gram stain is used for identification purposes. Gram-negative bacteria also have an outer layer of lipid, polysaccharide and protein. This causes fever and inflammation. It also causes the toxic effects of bacteria such as Salmonella. Some prokaryotes also have a slime layer called a glycocalyx. It is sticky and allows the bacteria to stick to surfaces, resist drying, resist immune responses and plays a role in creating biofilms. Pili- short hairlike projections that aid in attachment. Many prokaryotes can move. Taxismovement in response to stimuli. Flagella-whiplike projections that aid in movement. Two genera of gram-positive bacteria produce endospores(dormant, thick-walled structures that can survive harsh conditions. Once conditions improve, endospores germinate and develop. Ex. Clostridium botulinium and Bacillus anthacis B. Metabolic pathways may be useful in classification. Methods by which organisms acquire carbon and energy: autotrophs, heterotrophs, phototrophs, chemotrophs Oxygen requirements- obligate aerobes(require O2), obligate anaerobes (O2 is toxic), facultative anaerobes(with or without O2) Prokaryotes transmit DNA from generation to generation through vertical gene transfer. Binary fission- asexual reproduction – DNA replicates and then it is distributed to daughter cells Bacterial cells can divide every 20 minutes in the right conditions. New combinations of DNA can only be made by horizontal gene transfer. 3 types of horizontal gene transfer Transformation- bacteria takes in bits of DNA without contacting another cell. Transduction, a virus transfers combined DNA to a bacterial cell Conjugation- DNA is exchanged through a sex pilus Scientists have identified 23 phyla within domain Bacteria, but evolutionary relationships are not clear. Major phyla Proteobacteria-largest group of gram-negative bacteria. Includes purple sulphur bacteria, enteric bacteria(E. coli, Salmonella), vibrios(causes cholera) Cyanobacteria-autotrophs, some fix nitrogen, free living or symbiotic Spirochaetes- sprial shaped, cause lyme disease and syphilis Major phyla continued: Phylum firmicutes- gram positive, medically important, low proportion of G and C in DNA, cause tetanus, anthrax, strep and staph Phylum Actinobacteria- filamentous grampositive, high proportion of G and C in DNA, live in soil, source of antibiotics Phylum Chlamydiae- grow only in host cells, lack cell walls, cause chlamydia As new archaea are discovered we find that there are some that are do not live in hot, acid, or salty environments. 3 main phyla of Archaea Euryarchaeota-live in stagnant waters and anaerobic intestinal tracts, generate large quantities of methane gas, also includes photosynthetic halophiles. Phylum Crenarchaeota- includes acidophiles and thermophiles, but also contains a wide variety of soil and water microorganisms with moderate temperature requirements Phylum Korarchaeota- mostly known from genes extracted from the environment. Some are thermophiles. Microbes from vital links in ecosystems All species would die without bacteria and archaea. They are essential to carbon cycle, they are eaten by many organisms They are essential to nitrogen fixation, they make nitrogen useful to organisms. B. Bacteria and Archaea live in and on Us We are a habitat for microorganisms. They help us crowd out disease causing bacteria. Most bacteria living on us are harmless, some cause disease. Bacteria must enter the body to cause disease. They can enter by animal bite, inhaling, sexual activity, or ingesting contaminated food or water. Bacteria cause illness in a number of ways: damage caused by the bacteria, toxins produced by the bacteria, enzymes from the bacteria may damage tissues Sometimes bacteria can produce toxins that remain in poorly refrigerated or undercooked foods and people get sick from the toxins, not the bacteria themselves. Bacteria can also trigger immune responses. Many foods are produced by bacterial metabolism. Ex. Cheese, yogurt, vinegar Many microbes have industrial applications: ex. Vitamins, ethanol and acetone Transgenic bacteria produce insulin and blood clotting factors Bacteria are used in wastewater and sewage treatment. They also remediate pollutants.