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| Word / term | Definition |
|---|---|
NAD+ (nicotinamide adenine dinucleotide) | Abbreviation of nicotinamide adenine dinucleotide. NAD+ is a coenzyme present in all cells that helps enzymes transfer electrons during the redox reactions of metabolism |
NADP (nicotinamide adenine dinucleotide phosphate) | Abbreviation of nicotinamide adenine dinucleotide phosphate, a coenzyme that functions as an electron acceptor in the lightdependent reactions of photosynthesis. |
NADPH (nicotinamide adenine dinucleotide phosphate) | The reduced form of nicotinamide adenine dinucleotide phosphate which is used as an electron carrier. |
Nanometer | A unit of measure; one millionth (10-9) of a meter. |
Nanotechnology | A technology that creates small materials at the scale of molecules by manipulating single atoms. The name nano comes from the size of molecules which is measured in nanometers - or one billionth of a meter (0.000000001 meter). The dimension of single atoms is ten fold smaller. The molecular processes of life, particularly the activity of proteins (enzymes) and the self-organizing behavior of many biological molecules has greatly inspired nanotechnology and molecular motors (i.e. protein complexes) could be considered the result of natures nanotechnology. |
Naproxen | A non-steroidal anti-inflammatory drug (NSAID) used for the management of mild to moderate pain, fever, and inflammation . Naproxen blocks the enzyme cyclooxygenase that makes prostaglandins, resulting in lower concentrations of prostaglandins. As a consequence, inflammation, pain and fever are reduced. Brand names for naproxen include Anaprox, Naprelan, Naprosyn, and Aleve. |
Narcissistic personality disorder | Grandiose sense of self-importance of uniqueness; preoccupation with fantasies of limitless success; need for constant attention and admiration; disturbances in interpersonal relationships, such as lack of empathy, exploitativeness, and waivering between extremes of overidealization and devaluation. |
Narcolepsy | A sleep disorder syndrome consisting of excessive daytime sleep and disordered regulation of REM sleep. |
Nasal cannula | A low flow oxygen delivery device designed to administer oxygen through the nose, filling the anatomic reservoir with oxygen enriched gas. |
Nasality | A voice disorder in which a structural or functional inadequacy of the palate |
Nasogastric tube (NG Tube) | A plastic feeding tube placed in the nose and extended to the stomach. This tube allows for direct "tube feeding" to maintain the nutritional status of the patient or removal of stomach acids. |
Nasopharyngeal airway (see also Oropharyngeal airway) | An artificial airway that passes through the nose and nasopharynx and rests just behind the tongue, where it separates it from the posterior pharynx |
Native microflora | Microorganisms that are normally found within a food source (often referred to as spoilage organisms). |
Natural killer cell | A nonspecific defensive cell that attacks tumor cells and destroys infected body cells, especially those harboring viruses. |
Natural logarithm | The logarithm (log) to base e where e ≈ 2.718. The natural logarithm is represented by the symbol “ln”. |
Natural numbers | The counting numbers |
Natural selection | The process described by Darwin's theory of evolution that favors certain genotypes and disfavors others: Process by which the genotypes in a population that are best adapted to the environment increase in frequency relative to less well-adapted genotypes over a number of generations. |
Near infrared spectroscopy | A spectroscopic method utilising the near infra-red region of the electromagnetic spectrum (from 1100nm to 2500nm). |
Nearest-neighbour analysis | A technique of transferring radioactive atoms between adjacent nucleotides in DNA used to demonstrate that the two strands of DNA run in opposite directions. |
Necrosis | The death of living cells or tissues . Necrosis can be due, for example, to ischemia (lack of blood flow). From the Greek "nekros" (dead body). |
Necrotizing enterocolitis | A condition in which the intestine becomes inflamed, and there is sometimes death of the intestinal wall. This death of the intestinal wall results in a shortening of the intestine and subsequent nutritional malabsorption and poor growth. |
Nedd8 | A ubiquitin-like small protein modifier. |
Neddylation | The Nedd8 conjugation process, called neddylation, is similar to ubiquitination. |
Negative feedback | A process whereby a change in a physiological variable that is being monitored triggers a response that counteracts the initial fluctuation. |
Negative numbers | A real number less than zero. |
Nemadesmata | A type of ingestion rod. Stiff aggregates of many microtubules found around the cytostome of some ciliates and used during the ingestion of food. |
Nematocyst | A threadlike stinger, containing a poisonous or paralyzing substance, found in the cnidocyte of cnidarians. |
Nematoda | A phylum in the animal kingdom. Scientific name for nematode. A dominant group within the meiofauna. Scientific name for nematode. Commonly called roundworms. |
N-end rule | The life span of a protein is determined by its amino-terminal (N-terminal) amino acid. |
Neglect | Paying little or no attention to a part of the body. |
Neoendomics | Clusters of closely related species and subspecies that have evolved relatively recently. |
Neologisms | New words invented by the subject, distortions of words or standard words to which the subject has given new, highly idiosyncratic meaning; Nonsense or made-up word used when speaking. The person often does not realize that the word makes no sense. The judgement that neologisms are present should be made cautiously, taking into account the subject's educational and cultural background. Examples: "I was accused of midigation" (meaning the subject was accused of breaking the law). "They had an insinuating machine next door" (explaining how her neighbors were bothering her). Neologisms may be observed in schizophrenia and other psychotic disorders. |
Neonatal seizures | Seizures in newborns evidenced by alternating contractions of various muscle groups. |
Nephelometric turbidity unit (NTU) | Unit of measure for the turbidity of a solution such as water. |
Nephrolith | A kidney stone |
Nephron | The tubular excretory unit of the vertebrate kidney. |
Nephrosis | A non-inflammatory disease of kidneys |
Nernst equation | An equation for calculating the electrical potential difference across a cell membrane for a single permeating ion.
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Nerve | A collection of neuron fibres (axons and dendrites) wrapped up together tightly in connective tissue. |
Nerve fibre | A word to describe the axon of a neuron . |
Nerve impulse | Another name for the Action Potential: a rapid, transient, self-propagating change in electric potential across the membrane of an axon |
Nervous system | All the nerve cells of an animal; the receptor-conductor-effector system;. |
Net energy (of food) | Energy actually available for the body’s cells taking into account the extra heat produced by the transformation of nutrients after their absorption in the bloodstream. |
Network | A network is a set of hardware and software that allows more than one computer to share the same programs, data files, and peripheral equipment. |
Network File System (NFS) | A process for mounting magnetic disks on a network so that disks not physically attached to a computer appear as if they were physically attached. |
Neural crest | A band of cells along the border where the neural tube pinches off from the ectoderm. The cells of the neural crest migrate to various parts of the embryo and form the pigment cells in the skin, bones of the skull, the teeth, the adrenal glands, and parts of the Peripheral nervous system. |
Neuralgia | Paroxysmal pain that extends along the course of one or more nerves |
Neural groove | A dorsal, longitudinal groove that forms in a vertebrate embryo. It is bordered by two neural folds; preceded by the neural-plate stage and followed by the neural-tube stage. |
Neural plate | Thickened strip of ectoderm in early vertebrate embryos that forms along the dorsal side of the body. It gives rise to the Central nervous system. |
Neural stem cell | A stem cell found in adult neural tissue that can give rise to neurons and glial (supporting) cells |
Neural transplantation | A surgical procedure involving the transplantation of stem cells directly into the brain, close to the site of damage which is identified using brain-imaging technology. |
Neural tube | Primitive, hollow, dorsal nervous system of the early vertebrate embryo. The nervous system develops from a part of ectoderm lying originally on the dorsal side of the embryo, above the notochord and the somites. This part of the ectodermal layer thickens and becomes the neural plate, whose edges rise as neural folds that converge toward the midline, fuse together, and form the neural tube. In vertebrates the neural tube lies immediately above the notochord and extends beyond its anterior tip. The remainder of the ectoderm closes over the neural tube and becomes, in the main, the covering layer (epithelium) of the animal’s skin (epidermis). As the neural tube detaches itself from the overlying ectoderm, groups of cells pinch off and form the neural crest, which plays an important role in the development of, among other things, the segmental nerves of the brain and spinal cord. |
Neuromodulator | A chemical agent that is released by a neuron and diffuses through a local region of the central nervous system, acting on neurons within that region; generally has the effect of modulating the response to neurotransmitters rather than itself producing a response. |
Neuromuscular junction (NMJ) | The junction between an axon terminal of a motor neuron and a muscle fiber innervated by that motor neuron. At the NMJ the axon terminal of a motor neuron is typically branched, forming neuromuscular junctions with a number of different muscle fibers. |
Neurological | Having to do with the nerves or the nervous system. |
Neuron | Nerve cell. The fundamental unit of the nervous system, with structure and properties that allow it to conduct signals by taking advantage of the electrical charge across its cell membrane. |
Neuropsychologist | A psychologist who specializes in evaluating (by tests) brain/behavior relationships, planning training programs to help the survivor of brain injury return to normal functioning and recommending alternative cognitive and behavioral strategies to minimize the effects of brain injury. |
Neurosecretory cells | Cells in the hypothalamus that receive signals from other nerve cells, but instead of signaling to an adjacent nerve cell or muscle, release hormones into the bloodstream. |
Neurotransmitter | A chemical messenger released from the end of one neuron (it’s synaptic terminal) to move across a gap (the synaptic cleft) and then bind to receptors on a post-synaptic cell where it produces a response. Neurotransmitters are needed to carry information across the gap (the synaptic cleft) between one neuron and the next (the pre-synaptic and post-synaptic neurons) in the form of signalling known as chemical synaptic signalling. This is one of the most common methods of signalling in the nervous system. Binding of the neurotransmitter to the corresponding receptors on nearby cell surfaces (post synaptic membrane) causing a physiological stimulus in form of a membrane current (triggering action potentials) or second messenger cascade activating channels, pumps, kinases, or proteases. The molecular mechanisms of activation are similar to those of hormones. |
Neutralization | A reaction in which the characteristics of an acid or base disappear. |
Neutral variation | Genetic diversity that confers no apparent selective advantage. |
Neutron | An electrically neutral particle (a particle having no electrical charge), found in the atom. |
Neutrophils | Phagocytic (ingesting, scavenging) white blood cells that are produced in the bone marrow.They ingest and destroy invading microorganisms and facilitate post- infection tissue repair. Upon ingestion of pathogens, the neutrophil generates reactive oxygen species such as O2- (also known as free radicals). That O2- causes an influx of potassium ions into the portion of the neutrophil that contains the pathogen, which thereby releases proteases from existing granules ('storage' sites) in the neutrophil. The proteases then kill the pathogen. In addition to generating proteases, neutrophils can secrete collagenase and plasminogen activator. They are the immune system's "first line" of defense against invading pathogens, and large reserves are called forth within hours of the start of a "pathogen invasion." |
Neutrophil Extracellular Trap | A sort of mesh that is formed (e.g., in blood vessels) via the pathogen-triggered "programmed death" of immune system neutrophils. Chromatin and some protein molecules from the dead neutrophils adhere to each other; thereby forming the mesh (which entraps pathogens such as bacteria, for other immune system cells to kill). |
Neurocutaneous syndromes | A group of conditions that combine skin and sensory or nervous difficulties. |
Neurofibromatosis (NF) | An inherited, progressive neurological disorder in which tumor(s) are present in the tissues of the central nervous system (e.g., skin, brain). |
Neuropathic pain | Pain originating from a central or peripheral nervous system site rather than from a tissue or organ. The most common pain sensation, nociceptive pain, results from physical tissue damage, which is then transmitted to the brain by nerves to ultimately result in the perception of pain. A second type of pain, neuropathic pain, stems from a malfunction in the central and/or peripheral nervous system. Because its source is internal, neuropathic pain may lack an obvious origin. (see Nociceptive pain) |
Neuroplasticity | A general term used to describe the adaptive changes in the structure or function of nerve cells or groups of nerve cells in response to injuries to the nervous system or alterations in patterns of their use and disuse. |
Neuroses | Behavior that involves a partial disorganization, characterized by combinations of anxieties, compulsions, obsessions, and phobias. |
Neurotic disorder | A mental disorder in which the predominant disturbance is a symptom or group of symptoms distressing to the individual, recognized by him/her as unacceptable and alien (ego-dystonic); reality testing is grossly intact. Behavior does not actively violate gross social norms (though it may be quite disabling). The disturbance is relatively enduring or recurrent without treatment, and is not limited to a transitory reaction to stressors. There is no proven organic etiology or factor. |
Neurotic process | A specific etiological process involving the following sequence: |
Neuston | The environment of the interface between water and air, often rich in bacteria and protists. |
Neutral | Substance with a pH of 7.0. Substances with a pH rating close to neutral include meats and milk products (pH 6.4). |
Neurotransmitter | A chemical released from nerves that activates or inhibits the next nerve in the network, or some other type of cell. Neurotransmitters are used to transmit information (relayed along a nerve in the form of action potentials) from a neuron to the next cell in the series. They can act on the target cell generally only if the target cell has appropriate receptors to bind these chemicals. However, some neurons release gas molecules (nitric oxide and carbon monoxide have been discovered to carry out this role) which can act on the target cell without binding to specific receptors. |
Newlne character | One or two bytes which denote the end of a line. In DOS a newline character is two bytes: a carriage return and a linefeed. In UNIX a newline character is one byte: a linefeed. |
Newtons Laws of Motion | Classical laws which enable the prediction of the path of any object from a grain of sand to entire galaxies. |
NGVD | National Geodetic Vertical Datum. (1) As corrrected in 1929, a vertical control measure used as a reference for establishing varying elevations. (2) Elevation datum plane previously used by the Federal Emergency Management Agency (FEMA) for the determination of flood elevations. FEMA current uses the North American Vertical Datum Plane. |
NGVD-1929 | National Geodetic Vertical Datum of 1929. A geodetic datum derived from a general adjustment of the first order level nets of the United States and Canada. It was formerly called "Sea Level Datum of 1929" or "mean sea level" in the USGS series of reports. Although the datum was derived from the average sea level over a period of many years at 26 tide stations along the Atlantic, Gulf of Mexico, and Pacific Coasts, it does not necessarily represent local mean sea level at any particular place. |
nh | The slope of the Hill plot; the Hill coefficient. See Hill analysis. |
Niacin and niacinamide | Forms of Vitamin B3. Niacinamide can be made from niacin in the body. Niacin and niacinamide are required for the proper function of fats and sugars in the body and to maintain healthy cells. Only niacin seems to lower cholesterol, not niacinamide. It is most effective in increasing HDL cholesterol and modestly effective in lowering LDL cholesterol, and triglyceride levels. |
Niche | An organism’s role in its environment; the ecological position occupied by a species. |
Nick translation | A method for incorporating radioactive isotopes (typically 32P) into a piece of DNA. |
Niskin bottle | Quantitative sampling device for taking water samples below the surface. |
Nitrogen fixation | Biological assimilation of atmospheric nitrogen to form organic nitrogen-containing compounds. |
Nitric oxide | A gas that acts on blood vessels to relax them. |
Nitrification | The oxidation of ammonia or ammonium to nitrites and nitrates, as by nitrifying bacteria. |
Nitrite | Safe food additive that has been used for centuries to preserve meats, fish and poultry. It also contributes to the characteristic flavour, colour and texture of processed meats such as hot dogs. Because nitrite safeguards cured meats against the most deadly foodborne bacterium of all, Clostridium (C.) botulinum, its use is supported by the public health community. The human body generates much greater nitrite levels than are added to food. Nitrates consumed in foods such as carrots and green vegetables are converted to nitrite during digestion. Nitrite in the body is instrumental in promoting blood clotting, healing wounds and burns, and boosting immune function to kill tumor cells. |
Nitrogenase | An enzyme, unique to certain prokaryotes, that reduces N2 to NH3. |
Nitrogenous base | An organic base that contains the element nitrogen. A nitrogen- containing molecule having the chemical properties of a base. |
Nitrosamines | Digestive reaction-product of nitrite, a food additive used to preserve meats, fish and poultry. |
NMDA (N-methyl-D-aspartate) | A glutamate analog that is the agonist of Glutamte NMDA-type receptors. Glu-NMDA receptors are important for learning and memory and for particular long-term processes in the brain. |
Noble gases | Elements with zero valency. They form group 0 in the periodic table and are non-reactive. |
Nociceptive pain | Pain originating from injury to a peripheral tissue or organ. The most common pain sensation. Results from physical tissue damage, which is then transmitted to the brain by nerves to ultimately result in the perception of pain. (see Neuropathic pain) |
Nocturnal | Applied to organisms that are active during the hours of darkness. |
Node | A branching point in a phylogenetic tree, representing the common ancestor of the lineages descending from this branching point. |
Nodes of Ranvier | The small gaps in the myelin sheath between successive glial cells along the axon of a neuron. The nodes are the sites of of high concentration of voltage-gated ion channels, particularly voltage-gated Na+ channels. They are therefore important in regenerating the current for transmission of Action Potentials down the axon of a neuron. |
Noise signals | A signal (e.g., a sound or a visual stimulus) containing a wide range of frequencies with a specific distribution of energy across these frequencies. Different noise signals can vary systematically in the range of frequencies and the energy distribution across these frequencies. |
Noise suppression (in hearing aids) | Technologies implemented in hearing aids to reduce interference from unwanted “noise” in the environment, allowing the listener to be able to hear the desired signals more clearly. Some hearing aids have circuitry designed to control unwanted background noise, for example; automatic gain control, compression amplification, automatic signal processing, and noise suppression switches. Some hearing aids are programmable and use digital technology to automatically adjust hearing aid settings for different listening environments. |
Nomograph | A graph that allows a third variable to be measured when the values of two related variables are known. |
Non-ambulatory | Not able to walk. |
Non-coding sequences | Sequences of nucleotides that do not signal for proteins. |
Noncompetitive inhibitor | A substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing its conformation so that it no longer binds to the substrate. |
Noncyclic electron flow | A route of electron flow during the light reactions of photosynthesis that involves both photosystems and produces ATP, NADPH, and oxygen; the net electron flow is from water to NADP |
Noncyclic photophosporylation | The production of ATP by noncyclic electron flow. |
Nondisjunction | Chromosome pairs do not disjoin (separate) during cell division so that both chromosomes go to one daughter cell and none to the other. |
Non-equilibrium theory | Suggests that the number of species increases or decreases depending on how the environment influences species production, exchange and extinction at any particular time. |
Nonimmunoassay | A nonimmunoassay test (NIA) is a single set of samples which are measured on a detector instrument as a single batch but is not computed as an immunoassay. The measurements are printed as formatted raw data in a single report. |
Non-insulin-dependent diabetes (Type 2 diabetes) | A condition in which the body either makes too little insulin or cannot properly use the insulin it makes to convert blood glucose to energy. |
Non-ionizing radiation | Rays of energy that move in long, slow wave patterns and do not penetrate cells. |
Nonisotopic Assays | Nonisotopic assays are immunoassays which do not have radioactive labels for their tracer material. |
Nonlinear dynamics. | Seemingly random behaviour that can actually be described by chaos theory to actually be well defined, orderly, and sensitive to initial conditions. |
Nonparametric Tests | Nonparametric tests are statistical tests which make no assumptions about the distribution of a statistical population. Nonparametric tests are generally more robust but less sensitive than parametric tests |
Nonpolar covalent bond | A type of covalent bond in which electrons are shared equally between two atoms of similar electronegativity. |
non-point source (NPS) pollution | pollution discharged over a wide land area, not from one specific location. These are forms of diffuse pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities, which are carried to lakes and streams by surface runoff. Non-point source pollution is contamination that occurs when rainwater, snowmelt, or irrigation washes off plowed fields, city streets, or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants, such as nutrients and pesticides. |
Non self tapping screw | A screw that requires a tapping procedure in a predrilled guide hole before the screw can be inserted. See self-tapping screw, tap. |
Nonsense mutation | A mutation that changes an amino acid codon to one of the three stop codons, resulting in a shorter and usually nonfunctional protein. |
Nonspecific Binding | Nonspecific binding is the measurement of label or labeled conjugate present in the bound fraction of a ligand-binder reaction which occurred from nonimmune-specific means.Nonspecific binding is the only type of binding found in competitive binding immunoassay samples (NSB) having no binder present; and in sandwich binding immunoassay samples (Zero Blank) having no ligand present. Nonspecific binding samples as baseline standards can be used to represent infinitely high standard concentrations (competitive binding) or infinitely low standard concentrations (sandwich binding). |
Noonan syndrome | The adolescent growth spurt is often blunted or delayed and 60 percent of males have undescended testes. In addition to delay in growth, sexual development is variable and may also be delayed. Occurs in about 1 in 1,000 to 1 in 2,500 live births. The actual genetic abnormality has not yet been discovered. |
Noradrenaline | A hormone, produced by the medulla of the adrenal gland. The principal neurotransmitter in sympathetic nerves of the Autonomic Nervous System. It increases the concentration of glucose in the blood, raises blood pressure and heartbeat rate, and increases muscular power and resistance to fatigue; also one of the principal neurotransmitters; also called norepinephrine. |
Noradrenaline spillover | A measure of the rate of net production of the neurotransmitter noradrenaline from an organ. We use this as an index of the release of noradrenaline. |
Normal (in geometry) | Perpendicular |
Normal distribution | See Gaussian distribution |
Normal Solution | An outdated term referring to the concentration of an acid or base. It equals molarity times the number of hydrogen ions or hydroxyl ions generated by each molecule of acid or base respectively. Molarity is the preferred term. |
Normalized Response | The normalized response is the percentage of bound ligand-binder complex of the sample relative to a specified baseline standard, or standard, response within the assay run. Whereas the adjusted response measures the actual amount of ligand-binder binding which occurred in the sample, the normalized response measures the amount of binding relative to another sample within the assay run. This means that all of the binding variation between assay runs, which is due to binder deterioration, incubation differences, buffer changes, etc., are included in the adjusted response. These binding differences between assay runs are factored out of the normalized response. This allows the integrity of the sample itself to be examined without being distorted by differences in the binding conditions. |
Normalized variance | The normalized variance is the variance of the mean of the replicate samples' untransformed normalized response. |
Normalized coefficient of variance (CV) | The normalized CV is the coefficient of variation (standard deviation/mean) of the replicate samples' untransformed normalized response. |
Norm of reaction | The range of phenotypic possibilities for a single genotype, as influenced by the environment. |
Northern blot | A technique for analyzing mixtures of RNA, whereby the presence and rough size of one particular type of RNA (usually an mRNA) can be ascertained. |
Norwalk virus | Virus that contaminates raw oysters/shellfish, water and ice, salads, frosting, person-to-person contact. |
Notochord | A longitudinal, flexible rod formed from dorsal mesoderm and located between the gut and the nerve cord in all chordate embryos. |
Novosphingobium | Gram-negative rods |
NSB | Abbreviation for non-specific binding. It is the proportion of radioligand binding which is not displaced by other drugs specific for the receptor. It may consist of binding to other receptor types, to other proteins in the membrane, partitioning into lipids, or many other things. It is determined experimentally using a saturating concentration of a drug which, ideally, is chemically dissimilar to the radioligand but is specific for the same receptor. |
N-segment | Sequence of nucleotides added in a template-independant fashion at the joining junctions of heavy-chain immunoglobulin genes. |
Nuclear envelope (or Nuclear membrane) | The membrane in eukaryotes that encloses the nucleus, separating it from the cytoplasm. The double membrane which surrounds the eukaryotic nucleus. It has many pores in its surface which regulate the flow of large compounds into and out of the nucleus. |
Nuclear magnetic resonance (NMR) | The selective absorption of very high-frequency radio waves by certain atomic nuclei that are subjected to an appropriately strong stationary magnetic field. Nuclei in which at least one proton or one neutron is unpaired act like tiny magnets, and a strong magnetic field exerts a force that causes them to precess in somewhat the same way that the axes of spinning tops trace out cone-shaped surfaces while they precess in the Earth’s gravitational field. When the natural frequency of the precessing nuclear magnets corresponds to the frequency of a weak external radio wave striking the material, energy is absorbed from the radio wave. This selective absorption, called resonance, may be produced either by tuning the natural frequency of the nuclear magnets to that of a weak radio wave of fixed frequency or by tuning the frequency of the weak radio wave to that of the nuclear magnets (determined by the strong constant external magnetic field). |
Nuclear run-on | A method used to estimate the relative rate of transcription of a given gene, as opposed to the steady-state level of the mRNA transcript (which is influenced not just by transcription rates, but by the stability of the RNA).This technique is based on the assumption that a highly-transcribed gene should have more molecules of RNA polymerase bound to it than will the same gene in a less-active state. If properly prepared, isolated nuclei will continue to transcribe genes and incorporate 32P (radio-labelled phosphorus) into RNA, but only in those transcripts that were in progress at the time the nuclei were isolated. Once the polymerase molecules complete the transcript they have in progress, they should not be able to re-initiate transcription. If that is true, then the amount of radiolabel incorporated into a specific type of mRNA is theoretically proportional to the number of RNA polymerase complexes present on that gene at the time of isolation. A very difficult technique, rarely applied appropriately. |
Nuclease | An enzyme which degrades nucleic acids. A nuclease can be DNA-specific (a DNase), RNA-specific (RNase) or non-specific. It may act only on single stranded nucleic acids, or only on double-stranded nucleic acids, or it may be non-specific with respect to strandedness. A nuclease may degrade only from an end (an exonuclease), or may be able to start in the middle of a strand (an endonuclease). To further complicate matters, many enzymes have multiple functions; for example, Bal31 has a 3'-exonuclease activity on double-stranded DNA, and an endonuclease activity specific for single-stranded DNA or RNA. |
Nucleated | Having a nucleus. |
Nucleic acid | The collective name for DNA and RNA molecules found in every cell: A large molecule composed of nucleotide subunits. |
Nucleic acid probe | In DNA technology, a labeled single-stranded nucleic acid molecule used to tag a specific nucleotide sequence in a nucleic acid sample. Molecules of the probe hydrogen-bond to the complementary sequence wherever it occurs; radioactive or other labeling of the probe allows its location to be detected. |
Nucleoid | A dense region of DNA in a prokaryotic cell. |
Nucleoid region | The region in a prokaryotic cell consisting of a concentrated mass of DNA. |
Nucleolus | A specialized structure in the nucleus, formed from various chromosomes and active in the synthesis of ribosomes. An optically dense region (or regions) in a nucleus, associated with RNA synthesis. Not always visible. |
Nucleoside | An organic molecule consisting of a nitrogenous base joined to a five-carbon sugar. |
Nucleosome | The basic, beadlike unit of DNA packaging in eukaryotes, consisting of a segment of DNA wound around a protein core composed of two copies of each of four types of histone. |
Nucleotide | The building block of a nucleic acid, consisting of a five-carbon sugar covently bonded to a nitrogenous base and a phosphate group; A subunit of DNA or RNA consisting of a nitrogenous base (a purine or pyrimidine), a phosphate molecule, and a sugar molecule. Thousands of nucleotides are linked to form a DNA or RNA molecule. |
Nucleus | 1. An atom's central core, containing protons and neutrons. |
Nuclide | A nuclide is the nucleus of an atom having a specific atomic number and atomic mass number. A nuclide may be radioactive. |
Nudipodium | A type of unsupported pseudopodium without evident extrusomes. |
Null hypothesis | In statistical analysis, a hypothesis proposing that there is no statistically significant difference between the observed results of an experiment and the expected results. |
Null set | Same as empty set. A set with no elements. |
Number line | A line on which every point represents a real number. |
Numeral | A symbol that stands for a number. |
Numerator | The top number in a fraction.
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Nutraceuticals | Chemicals that have beneficial effects (pharmacological effects) on our physiology if taken in appropriate amounts with food. Plants are the major source of nutraceuticals also known as phytochemicals. Plants produce those molecules for self-defense or to attract insects and animals to facilitate pollen distribution. For the latter purpose, they often are colorants while tasting bitter to ward of animals. |
Nutrient | Molecules that can be used by cells or living organism to extract energy through metabolic processes. Although nutrients are often sought off only as energy providers, they can also be used as molecular building block for the biosynthesis of cellular structures. |
Nutrient density | Nutrient dense foods are those that provide substantial amounts of vitamins and minerals and relatively fewer calories. The opposite of nutrient dense is calorie dense which are foods that mainly supply calories and relatively few nutrients. |
Nyctalopia | Congenital night blindness caused by a lack of rod functioning in the retina |
Nymph | In aquatic insects, the larval stage. |
Nystagmus | Uncontrolled, involuntary rhythmic horizontal, vertical, or rotary rapid eye movements which may be congenital or acquired. Usually occurs in response to movement of the head. |
Where V = voltage difference, R = Universal gas constant, z = valency of the ion,