0.5 Glossary  (Page 12/18)

N

• naïve mature B cell a B cell that has not yet been activated
• naked virus virus composed of a nucleic acid core, either DNA or RNA, surrounded by a capsid
• nalidixic acid member of the quinolone family that functions by inhibiting the activity of DNA gyrase, blocking DNA replication
• narrow-spectrum antimicrobial drug that targets only a specific subset of microbes
• nasal cavity air-filled space in the skull immediately behind the nose
• nasolacrimal duct tear duct connecting the lacrimal glands to the nasal cavity
• nasolacrimal duct tear fluid flows from each eye through this duct to the inner nose
• nasopharynx part of the upper throat (pharynx) extending from the posterior nasal cavity; carries air inhaled through the nose
• native structure three-dimensional structure of folded fully functional proteins
• natural active immunity immunity that develops as a result of natural infection with a pathogen
• natural antibiotic antimicrobial compound that is produced naturally by microorganisms in nature
• natural killer cells (NK cells) lymphoid cells that recognize and destroy abnormal target cells by inducing apoptosis
• natural passive immunity transfer of maternal antibodies from mother to fetus (transplacentally) or infant (via breastmilk)
• necrotizing fasciitis a serious infection, also known as flesh-eating disease, that leads to rapid destruction of tissue through the action of exotoxin A; it can be caused by S. pyogenes or several other bacterial species
• negative (–) single-strand RNA (–ssRNA) a viral RNA strand that cannot be translated until it is replicated into positive single-strand RNA by viral RNA-dependent RNA polymerase
• negative stain a stain that produces color around the structure of interest while not coloring the structure itself
• Nematoda phylum comprising roundworms
• neonatal herpes herpes infection of the newborn, generally caused by infection during birth
• neonatal meningitis meningitis caused by Group B streptococcus and occurring primarily in neonates (less than 2 months old)
• neonatal tetanus tetanus acquired through infection of the cut umbilical cord
• neurocysticercosis parasitic invasion of brain tissues by the larvae of the pork tapeworm, Taenia solium
• neuromycosis any fungal infection of the nervous system
• neuron specialized cell found throughout the nervous system that transmits signals through the nervous system using electrochemical processes
• neuropathy numbness or tingling sensation caused by damage to peripheral nerves
• neurotoxoplasmosis disease caused by the invasion of brain tissues by the protozoan Toxoplasma gondii ; typically only affects immunocompromised patients
• neurotransmitter compound that is released at the synapse of neurons to stimulate or suppress the actions of other cells
• neutralism type of symbiosis that does not affect either of the two populations
• neutralization binding of an antibody to a pathogen or toxin, preventing attachment to target cells
• neutrophile organism that grows best at a near a neutral pH of 6.5–7.5
• neutrophils leukocytes with a multilobed nucleus found in large numbers in peripheral blood; able to leave the bloodstream to phagocytose pathogens in infected tissues; also called polymorphonuclear neutrophils (PMNs)
• next generation sequencing a group of automated techniques used for rapid DNA sequencing
• nicotine adenine dinucleotide (NAD ⁺ /NADH) oxidized/reduced forms of an electron carrier in cells
• nicotine adenine dinucleotide phosphate (NADP ⁺ /NADPH) oxidized/reduced forms of an electron carrier in cells
• nitrogen fixation bacterial biochemical pathways that incorporate inorganic nitrogen gas into organic forms more easily used by other organisms
• nitrogenous base nitrogen-containing ring structure within a nucleotide that is responsible for complementary base pairing between nucleic acid strands
• noncoding DNA regions of an organism’s genome that, unlike genes, do not encode proteins
• noncommunicable disease disease that is not transmitted from one person to another
• noncompetitive (allosteric) inhibitor molecule that binds to allosteric sites, inducing a conformational change in the enzyme’s structure that prevents it from functioning
• noncritical item object that may contact intact skin but does not penetrate it; requires cleanliness but not a high level of disinfection
• noncyclic photophosphorylation pathway used in photosynthetic organisms when both ATP and NADPH are required by the cell
• nonenveloped virus naked virus
• nongonococcal urethritis (NGU) a nonspecific infection of the urethra that is not caused by Neisseria gonorrheae
• noninfectious disease disease caused by something other than an infectious agent (e.g., genetics, environment, nutritional deficiencies)
• nonionizing radiation low-energy radiation, like ultraviolet light, that can induce dimer formation between two adjacent pyrimidine bases, resulting in DNA polymerase stalling and possible formation of a frameshift mutation
• nonsense mutation point mutation that converts a codon encoding an amino acid (a sense codon) into a stop codon (a nonsense codon)
• nontreponemal serologic tests qualitative and quantitative indirect diagnostic tests for syphilis
• northern blot a technique in molecular genetics used to detect the amount of RNA made by gene expression within a tissue or organism sample; RNA fragments within a sample are separated by agarose gel electrophoresis, immobilized on a membrane, and then exposed to a specific DNA probe labeled with a radioactive or fluorescent molecular beacon to aid in detection
• nosocomial disease disease acquired in a hospital setting
• notifiable disease a disease for which all cases must legally be reported to regional, state, and/or federal public health agencies
• nuclear envelope (also called the nuclear membrane) a structure defining the boundary of the nucleus; composed of two distinct lipid bilayers that are contiguous with each other and with the endoplasmic reticulum
• nuclear lamina a meshwork of intermediate filaments (mainly lamins) found just inside the nuclear envelope; provides structural support to the nucleus
• nucleic acid class of macromolecules composed of nucleotide monomers polymerized into strands
• nucleoid concentrated area of DNA genome and associated proteins found in a prokaryotic cell that is not surrounded by a membrane
• nucleoid-associated protein (NAP) protein that assists in the organization and packaging of the chromosome in prokaryotic cells
• nucleolus a dense region within the nucleus where ribosomal RNA biosynthesis occurs and preribosomal complexes are made
• nucleoside analog chemical that is structurally similar to a normal nucleotide base that can be incorporated into DNA instead of normal bases during replication but that has different base pairing rules than the normal base for which it was substituted, inducing mutation
• nucleotide excision repair (dark repair) enzymatic mechanism to repair pyrimidine dimers by cutting the dimer-containing DNA strand on both sides of dimer, removing the intervening strand and replacing the bases with the correct ones
• nucleotide nucleic acid monomer composed of a pentose sugar, a phosphate group, and a nitrogenous base
• nucleus a membrane-bound structure of eukaryotic cells that houses the DNA genome
• numerical aperture a measure of a lens’s ability to gather light