Glossary 21 Prokaryotes and Viruses

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Glossary Prokaryotes and Viruses Chapter 21 archaebacterium bacillus (bacilli) bacterial chromosome bacteriophage cell wall coccus (cocci) conjugation disease emerging pathogen endospore epidemic eubacterium extreme halophile extreme thermophile fruiting body glycocalyx Gram stain Member of the prokaryotic domain Archaebacteria Rod-shaped prokaryotic cell. Circularized, doublestranded DNA molecule with few proteins. Category of viruses that infect bacterial cells. A semirigid, permeable struct
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  Glossary Prokaryotes and Viruses Chapter 21archaebacterium Member of the prokaryotic domain Archaebacteria bacillus (bacilli) Rod-shaped prokaryotic cell. bacterialchromosome Circularized, doublestranded DNA molecule with few proteins. bacteriophage Category of viruses that infect bacterial cells. cell wall A semirigid, permeable structure external to the plasma membrane; helps manycells retain their shape and resist rupturing. coccus (cocci) Spherically shaped prokaryotic cell. conjugation Prokaryotic gene transfer mode; also protistan sexual reproductive mode. disease Outcome of infection when defenses aren't mobilized fast enough and apathogen's activities interfere with normal body functions. emergingpathogen Deadly pathogen, either a newly mutated or newly opportunistic strain. endospore Resting structure formed by some bacteria; encloses a duplicate of the bacterialchromosome and a portion of cytoplasm. epidemic Rapid spread, then subsidence, of a disease within a population. eubacterium Prokaryotic cell; has a nucleoid, but no nucleus, cytoplasm, or cell membrane;most have a cell wall, some encapsulated. extreme halophile Archaebacterium of unusually saline habitats (e.g., salt lakes). extremethermophile Archaebacterium of very hot aquatic habitats (e.g., hot springs). fruiting body Spore-bearing structures formed by some bacteria, fungi. glycocalyx Sticky mesh forming a capsule or slime layer around a bacterial cell wall. Gram stain A sample of cells is exposed to purple dye, then iodine, then an alcohol washand counterstain. Cell walls of Gram-positive species stay purple; Gram-negative turn pink. heterocyst Cyanobacterial cell, self-modified, that synthesizes a nitrogen-fixing enzymewhen nitrogen supplies dwindle. infection Invasion and multiplication of a pathogen in a host. Disease follows if defensesare not mobilized fast enough; the pathogen's activities interfere with normalbody functions. lysis Gross damage to a plasma membrane, cell wall, or both that lets the cytoplasmleak out; causes cell death. lysogenicpathway Latent period that extends many viral replication cycles. Viral genes getintegrated into host chromosome and may stay inactivated through many hostcell divisions but eventually are replicated in host progeny. lytic pathway Of viruses, a rapid replication pathway that ends with lysis of host cell. methanogen Anaerobic archaebacterium that produces methane gas as by-product. microorganism Organism, usually single celled, too small to be observed without a microscope. numericaltaxonomy Study of the degree of relatedness between an unidentified organism and aknown group through comparisons of traits. Used to classify prokaryotic species.  pandemic An epidemic that breaks out in several countries at the same time. pathogen Any virus, bacterium, fungus, protistan, or parasitic worm that can infect anorganism, multiply in it, and cause disease. pilus (pili) Short, filamentous protein projecting above cell wall to help it adhere tosurfaces. plasmid A small, circular molecule of extra bacterial DNA that carries a few genes and isreplicated independently of the chromosome. prion Small infectious protein that causes rare, fatal degenerative diseases of nervoussystem. prokaryotic cell Archaebacterium or eubacterium; single-celled organism, most often walled;lacks the profusion of membranebound organelles observed in eukaryotic cells. prokaryoticfission Cell division mechanism by which prokaryotic cells alone reproduce. spirillum (spirilla) A corkscrew-shaped prokaryotic cell. strain (bacterial) Compared to an organism of a known type, an organism with differences thatare too minor to classify it as a separate species (e.g., Escherichia coli  strain018:K1:H). viroid Infectious particle of short, tightly folded strands or circles of RNA. virus A noncellular infectious agent made of DNA or RNA, a protein coat and, insome, an outer lipid envelope; it can be replicated only after its genetic materialenters a host cell and subverts the host's metabolic machinery.
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