Chapter 20 Biology Dallas

Virus

Nonliving infectious particle with a DNA or RNA genome that can replicate only by using a host cell's metabolic machinery; has no metabolism and does not respond to stimuli

Capsid

Outer protein coat of a virus, made of protein subunits, that surrounds the nucleic acid core

Viral envelope

Outer layer on some viruses, usually partly host plasma membrane with viral glycoprotein spikes

Naked virus

A virus that has a capsid but no envelope external to it

Glycoprotein spikes

Viral envelope proteins that attach to host cell receptors and are used to classify virus subtypes

International Committee on Taxonomy of Viruses (ICTV)

Group that developed the virus classification system, which uses only the levels of order, family, genus, and species

Obligate intracellular parasite

Organism (such as a virus) that cannot multiply outside a living cell and must infect a living cell to reproduce

Host specificity

Viruses can reproduce only in cells of specific organisms because capsid or envelope spikes bind specific receptor sites on the host cell surface

Five steps of the viral reproductive cycle

Attachment, penetration, biosynthesis, maturation, and release

Bacteriophage

A virus that parasitizes bacteria; used by scientists to study the viral reproductive cycle

Lytic cycle

Viral cycle in which the host cell is lysed at the end and new viruses are released

Lysogenic cycle

Viral cycle in which the virus incorporates its DNA into the host bacterial DNA and is latent for a time before actively replicating

Prophage

Latent viral DNA that is incorporated into the bacterial DNA and replicated along with it

Lysogenic cells

Cells that carry a copy of the prophage genome

Uncoating

Removal of the viral envelope and capsid after an animal virus enters a host cell, freeing the viral genome

Budding

Release of mature enveloped viruses from a host cell, taking a piece of host membrane as their envelope

Retrovirus

Animal virus with an RNA genome that is converted into DNA (example: HIV)

Reverse transcriptase

Retroviral enzyme that uses RNA as a template to make cDNA

cDNA

Complementary DNA strand made from viral RNA; it is integrated into host DNA and replicated with it

Antiretroviral drugs

Drugs that interfere with one or more steps of HIV reproduction and can delay the emergence of AIDS

Emerging virus

New or previously uncommon virus that infects a large number of humans (examples: Zika, MERS, AIDS, West Nile, Ebola, avian influenza)

Hemagglutinin (H spike)

Flu virus spike that allows the virus to bind to its host cell receptor; at least 16 types exist

Neuraminidase (N spike)

Flu virus spike that attacks host plasma membranes so mature viruses can exit the cell; at least 9 types exist

H5N1

Bird flu subtype named for its H5 and N1 spikes; common in waterfowl and poultry and a concern for becoming a pandemic

Flu pandemic

Widespread outbreak that may occur when a new flu virus arises and there is little or no immunity in the human population

Zika virus

Virus spread by Aedes mosquitoes, from mother to fetus (causing microcephaly), and through sexual contact; symptoms include rash, conjunctivitis, fever, and joint pain

Microcephaly

Condition of a small head and underdeveloped brain in babies, linked to Zika infection of the fetus

Aedes mosquito

Mosquito that spreads Zika, dengue fever, chikungunya, and yellow fever

Anopheles mosquito

Mosquito that spreads malaria

Viroid

Naked strand of RNA that causes about a dozen crop diseases by directing the cell to produce more viroids

Prion

Proteinaceous infectious particle; a misfolded protein that infects by altering the structure of a normal protein; cannot replicate on its own

Transmissible spongiform encephalopathies (TSEs)

Untreatable, fatal neurodegenerative diseases caused by prions that destroy brain nerve tissue

Mad cow disease

Bovine spongiform encephalopathy; a prion disease transmissible to humans by eating contaminated cattle brain or meat

Prokaryote

Single-celled organism lacking a eukaryotic nucleus; includes bacteria and archaea (means "before a nucleus")

Antonie van Leeuwenhoek

Scientist who first described prokaryotes in the seventeenth century

Spontaneous generation

Disproved idea that living things arise from inanimate matter; Pasteur's experiment (c. 1850) showed bacteria in air contaminated media

Glycocalyx

Organized capsule that may surround the prokaryotic cell wall and protect parasitic cells from host defenses

S-layer

Loose gelatinous sheath that may surround the prokaryotic cell wall

Flagellum (prokaryotic)

Structure for movement made of a flagellin filament, a hook, and a basal body; rotates 360 degrees to spin the cell forward

Flagellin

Protein that makes up the filament of a prokaryotic flagellum

Fimbriae

Short, bristlelike filaments on prokaryotes that allow adherence to surfaces; in pathogens they determine which host cells are bound

Nucleoid

Dense area in a prokaryote where the single, circular chromosome is located

Plasmid

Accessory ring of DNA in prokaryotes with genes for antibiotic resistance, toxin production, or chemical degradation; used in genetic engineering

Prokaryotic ribosomes

Smaller than eukaryotic ribosomes; carry out protein synthesis in prokaryotes

Synthetic biology

Field in which new biological processes or organisms are genetically designed or constructed for useful purposes; a main focus of DIY biology

Green fluorescent protein (GFP)

Protein that glows under ultraviolet light; its gene is used in the DIY glowing plant project

Agrobacterium tumefaciens

Soil bacterium used to deliver foreign genes into plant cells in plant transformation

Binary fission

Asexual reproduction in prokaryotes in which a parent cell splits into two daughter cells

Conjugation

Transfer of DNA (a plasmid) from one bacterium to another through a conjugation pilus

Conjugation pilus

Tube that temporarily joins two bacterial cells during conjugation

Transformation

Genetic recombination in which bacteria take up free pieces of DNA released by live or dead bacteria

Transduction

Genetic recombination in which bacteriophages transfer portions of bacterial DNA from one cell to another

Bacteria

The more common type of prokaryote; their biomass on Earth exceeds that of plants and animals combined

Peptidoglycan

Complex of polysaccharides linked by amino acids that protects bacterial cell walls

Gram stain

Procedure that differentiates bacteria by cell wall structure

Gram-positive bacteria

Bacteria with a thick peptidoglycan layer that stain purple

Gram-negative bacteria

Bacteria with a thin peptidoglycan layer that stain red

Coccus

Round or spherical bacterial cell shape

Bacillus

Rod-shaped bacterial cell shape

Spirillum

Spiral- or helical-shaped bacterial cell shape

Aerobic bacteria

Bacteria that require a constant supply of oxygen for cellular respiration (most bacteria)

Facultative anaerobe

Organism able to grow in either the presence or absence of gaseous O2

Obligate anaerobe

Organism unable to grow in the presence of O2 (examples: bacteria causing botulism, gas gangrene, and tetanus)

Photoautotroph

Photosynthetic organism that uses light energy to assemble the organic molecules it needs

Anoxygenic photosynthetic bacteria

Bacteria (green and purple sulfur bacteria) that use only photosystem I with bacteriochlorophyll and do not give off O2

Oxygenic photosynthetic bacteria

Bacteria (cyanobacteria) that use photosystems I and II with plant-type chlorophylls and produce O2 as a by-product

Chemoautotroph

Bacterium that carries out chemosynthesis, making organic molecules using energy from oxidizing inorganic compounds (such as H2, H2S, and NH3)

Nitrifying bacteria

Chemoautotrophs that oxidize ammonia (NH3) to nitrites (NO2) and nitrites to nitrates (NO3)

Chemoheterotroph

Organism that obtains carbon and energy from organic nutrients produced by other living organisms

Saprotroph

Chemoheterotrophic bacterium that acts as a decomposer, breaking down dead organic matter and recycling matter

Symbiotic relationship

Close relationship in which two different species live together in an intimate way

Mutualism

Symbiosis in which both species benefit (example: intestinal bacteria release vitamins K and B12 for humans)

Commensalism

Symbiosis in which one population modifies the environment so a second population benefits (example: E. coli uses up oxygen, letting obligate anaerobes live in the intestine)

Parasitism

Symbiosis in which parasitic bacteria feed on the tissues and fluids of a living host and cause disease

Pathogen

Parasitic microbe that causes disease

Toxin

Small organic molecule, protein piece, or cell wall part released by microbes that is the pathological portion causing disease

Endospore

Resistant structure formed by some bacteria under unfavorable conditions; has three protective coats and is a means of survival and dispersal, not reproduction

Erythromycin and tetracyclines

Antibiotics that inhibit bacterial protein synthesis by affecting bacterial ribosomes

Penicillin, ampicillin, and fluoroquinolone

Antibiotics that inhibit bacterial cell wall synthesis by blocking peptidoglycan formation

Antibiotic resistance

Increasing bacterial resistance due to excessive and improper antibiotic use; resistance genes can spread by transformation, conjugation, or transduction

MRSA

Methicillin-resistant Staphylococcus aureus; strain responsible for many difficult-to-treat infections

Cyanobacteria

Gram-negative, oxygenic photosynthetic bacteria (formerly called blue-green algae) believed to have introduced O2 into the primitive atmosphere

Heterocyst

Thick-walled cyanobacterial cell without a nucleus where nitrogen fixation occurs

Lichen

Symbiosis in which cyanobacteria provide organic nutrients to a fungus, and the fungus protects them and supplies inorganic nutrients

Cyanobacterial bloom

Population boom caused by nitrates and phosphates in water; when they die, decomposers use up oxygen and fish die

Archaea

Prokaryotes with distinct molecular traits, including a different rRNA base sequence than bacteria; lack peptidoglycan in their cell walls

Archaeal plasma membrane lipids

Unusual lipids of glycerol linked to hydrocarbons (not fatty acids) that allow function at high temperatures

Halophile

Archaeon that requires high salt concentrations (12-15%), such as in the Great Salt Lake; aerobic chemoheterotroph

Thermoacidophile

Archaeon living in hot, acidic environments (pH 1-2, above 80 C); chemoautotrophic anaerobe using H2 as electron donor and sulfur as terminal electron acceptor

Methanogen

Anaerobic archaeon (found in marshes) that uses H2 to reduce CO2 to methane and couples this to ATP production