18.1 Studying Viruses and Prokaryotes

CHAPTER18@ CLASSZONE.COMKEY CONCEPTS Vocabulary Games Concept Maps Animated Biology Online Quiz18.1 Studying Viruses and ProkaryotesInfections can be caused in several ways. Viruses,viroids, and prions have characteristics ofboth living and nonliving things.Unlike bacteria, viruses cannotreproduce on their own. A virushas genetic material and aprotein coat. Viroids haveonly RNA and no protein coat.Prions are made of only protein.18.2 Viral Structure and ReproductionViruses exist in a variety of shapes and sizes.Viruses can be helical like aspring, many-sided, or enveloped.Bacteriophages, orviruses that attack bacteria,have a many-sided capsidwith a long protein tail andspiky footlike fibers. Thereare two basic types of viral infections: lytic andlysogenic. A lytic infection results in the host cellsbursting open, while the virions in a lysogenicinfection do not immediately destroy the host.18.3 Viral DiseasesSome viral diseases can be prevented withvaccines. Viruses can enter a body throughwounds or body openings such as mouths ornoses. Many infectious viruses exist. Examples ofillnesses caused by viruses include the commoncold, influenza, SARS, and AIDS. Vaccines canprevent some, but not all, viral diseases.18.4 Bacteria and ArchaeaBacteria and archaea are both single-celledprokaryotes. Prokaryotes are widespread onEarth. Archaea look very similar to bacteria, butmany of their structures are made of differentcompounds. Some prokaryotes can survive harshconditions by forming endospores. Prokaryotescan transfer genes to each other throughconjugation.18.5 Beneficial Roles of ProkaryotesProkaryotes perform important functions fororganisms and ecosystems. Prokaryotes that livein an animal’s digestive tract help the animalabsorb nutrients from the food that it eats. Animalsand plants also depend on prokaryotes tofix atmospheric nitrogen. Nitrogen is necessaryto make amino acids and proteins. Bioremediationuses prokaryotes to help break down pollutantsin the environment.18.6 Bacterial Diseases and AntibioticsUnderstanding bacteria is necessary to preventand treat disease. Although the majority of bacteriaare not pathogenic, some do cause disease.Bacteria can also cause conditions such as foodpoisoning, chronic acne, Lyme disease, and toothdecay. Antibiotics are used to fight bacterialinfection. However, through natural selection,many bacteria have become resistant to commonlyused antibiotics.Synthesize Your NotesConcept Map Use a concept map like the one below tosummarize what you know about infectious agents. Includedetails about genetic material and types of hosts theyinfect.infectiousdiseasesincludeincludeCycle Diagram Use two cycle diagrams like the one belowto summarize lytic and lysogenic infections.viral DNA entershost cellprionstraits traits traits traits568 Unit 6: Classification and Diversity