Viruses, Bacteria, and Archaea

viruses

noncellular parasitic agent consisting of an outer capsid and an inner core of nucleic acid

capsid

protective protein containing the genetic material of a virus

lytic cycle

bacteriophage life cycle in which the virus takes over the operation of the bacterium immediately upon entering it and subsequently destroys the bacterium

lysogenic cycle

bacteriophage life cycle in which the virus incorporates its DNA into that of a bacterium; occurs preliminary to the lytic cycle

lysogenic cell

cell that contains a prophage (virus incorporated into DNA), which is replicated when the cell divides

bacteriophages

virus that infects bacteria

retroviruses

RNA virus containing the enzyme reverse transcriptase that carries out RNA/DNA transcription

reverse transcriptase

viral enzyme found in retroviruses that is capable of converting their RNA genome into a DNA copy

viroids

infectious strand of RNA devoid of a capsid and much smaller than a virus

prions

infectious particle consisting of protein only and no nucleic acid. Prions can cause normal proteins to misfold

neurodegenerative diseases

disease, usually caused by a prion, virus, or bacterium, that damages or impairs the function of nervous tissue

emerging diseases

an infectious disease, usually caused by a virus or bacterium, that has not previously been detected in humans

emerging viruses

newly identified viruses that are becoming more prominent, usually because they cause serious disease

prokaryotes

organism that lacks the membrane-bound nucleus and the membranous organelles typical of eukaryotes

binary fission

splitting of a parent cell into two daughter cells; serves as an asexual form of reproduction in bacteria

conjugation

transfer of genetic material from one cell to another

conjugation pilus

in a bacterium, elongated, hollow appendage used to transfer DNA to other cells

transformation

taking up of extraneous genetic material from the environment by bacteria

transduction

exchange of DNA between bacteria by means of a bacteriophage

bacteria

member of the domain Bacteria

peptidoglycan

polysaccharide that contains short chains of amino acids; found in bacterial cell walls

facultative anaerobes

prokaryote that is able to grow in either the presence or the absence of gaseous oxygen

obligate anaerobes

prokaryote unable to grow in the presence of free oxygen

photoautotrophs

organism able to synthesize organic molecules by using carbon dioxide as the carbon source and sunlight as the energy source

chemoautotrophs

organism able to synthesize organic molecules by using carbon dioxide as the carbon source and the oxidation of an inorganic substance (such as hydrogen sulfide) as the energy source

chemoheterotrophic

organism able to synthesize organic molecules by using carbon dioxide as the carbon source and the oxidation of an inorganic substance (such as hydrogen sulfide) as the energy source

saprotrophs

organism that secretes digestive enzymes and absorbs the resulting nutrients back across the plasma membrane

lichens

symbiotic relationship between one or two certain fungi and either cyanobacteria or algae, in which the fungi possibly provide inorganic food or water and the algae or cyanobacteria provide organic food

mutualism

symbiotic relationship in which both species benefit in terms of growth and reproduction

commensalism

symbiotic relationship in which one species is benefited, and the other is neither harmed nor benefited

parasitism

symbiotic relationship in which one species (the parasite) benefits in terms of growth and reproduction to the detriment of the other species (the host)

pathogens

disease-causing agents, such as viruses, parasitic bacteria, fungi, and animals

toxins

Poisonous substance produced by living cells or organisms. Toxins are often proteins that are capable of causing disease on contact with or absorption by body tissues

endospores

spore formed within a cell; certain bacteria form endospores

cyanobacteria

photosynthetic bacterium that contains chlorophyll and releases oxygen; formerly called a blue-green alga

archaea

prokaryotic organisms that are members of the domain Archaea

halophiles

type of archaean that lives in extremely salty habitats

thermoacidophiles

type of archaean that lives in hot, acidic, aquatic habitats, such as hot springs or near hydrothermal vents

methanogens

type of archaean that lives in oxygen-free habitats, such as swamps, and releases methane gas