Glossary of Scientific Terms

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Absorption
(a) In physiology: aprocess by which nutrients move from the lower digestive tract (small and large intestine or colon) into the blood stream to be utilized by the body.
(b) In spectroscopy: the interaction between atoms and radiation (light, X-rays, UV, infrared), where some of the energy of the radiation is absorbed by the electrons of the atoms, increasing their energy content. The loss of intensity of the radiation (e.g. reduced light intensity) can be measured and is an indicator of the structural state of the molecules that absorb the radiation.

Action Potential
A spontaneous self-propagating change in membrane potential that travels as a 'wave' along electrically excitable cell membranes found in neurons and muscle cells. Action potentials are triggered when the cell's membrane potential depolarizes (i.e. becomes more positive with respect to the internal side) beyond a threshold value of usually -40mV. Voltage sensitive ion channels (Na and K channels) open and close in fast succession causing first in influx of sodium ions (making the inside more positive = depolarization) followed by potassium efflux (making the outside more positive and inside more negative = hyperpolarization). The potassium efflux brings the membrane potential below the threshold and thus to rest. A new action potential can only be triggered with a new stimulus which comes from neurotransmitter activated ion channels at locations of synaptic interaction between neurons or neurons and muscle cells.

Adaptation
A process in biological evolution as the result of natural selection where a species becomes better adjusted to the living conditions of its environment (temperature, food sources, and predators). In adaptation, individuals that have the most offspring contribute more of their genetic makeup to the next generation. Beneficial traits are favored in this editing process and the next generation of a species or population (for instance a smaller geographical subset of a species) is better adapted to new environmental conditions that caused certain individuals to have fewer offspring. Thus genes that are not optimal for certain conditions will become rarer as a result. Adaptation, as evolution in general, is studied at the level of a population of interbreeding individuals.

Adult Stem Cell
A specialized cell that is needed for growth, wound healing and tissue regeneration. Adult stem cells are found in all tissues and organs of animals and plants.

Allele
The genetic variant of a gene. A gene can be found in different variants in a population, even in the same individual. Alleles are responsible for the different traits of certain characteristics, such as eye and hair color in animals, and flower and seed color in plants. Alleles are also responsible for genetic diseases.

Amino Acid
Building block of proteins and enzymes. Dietary proteins need to be broken into their amino acid components before they can be used by the body. Note that there are 20 amino acids found in proteins. Many nutritional lists describe only 18 occluding glutamine and asparagine. Their values are included in those reported for the acidic forms glutamate and aspartate.

Anabolism
Biosynthesis of molecules in cells and part of metabolism.

Antioxidant
A molecule that protects cells from oxidative damage of oxygen and free radical molecules that are chemically unstable and cause random reactions damaging proteins, nucleic acids, and cell membranes. Examples of dietary antioxidants are vitamins C, E, and K, and diverse plant products such as lycopene, a nutraceutical found in tomatoes.

Aperiodic
Refers to the lack of symmetry in molecular structures or functions. An important insight into the mechanism of biological structures is their aperiodic composition and distribution of atoms causing the extraordinary complexity of cells.

Archaea
A prokaryotic form of life that forms a domain in the tree of life. There are three domains: bacteria, archaea, and eukarya. Bacteria are also prokaryotic organisms. Eukaryotes include animals, plants, fungi, and protozoan and have very different cell structures, bigger and with internal membrane bound structures (organelles). While bacteria and archaea look similar in structure, they have very different metabolic and genetic activity. One defining physiological characteristic of archaea is their ability to live in extreme environments. They are often called extremophiles and unlike bacteria and eukarya depend on either high salt, high or low temperature, high pressure, or high or low pH.

Atom (atomistic)
The smallest unit of matter as recognized by chemical properties of molecules. Atoms are composed of protons, neutrons and electrons. The latter provide all properties described by molecular interactions and chemical reactions that are essential processes in biology.

ATP
Short for Adenosine triphosphate, a nucleotide and universal energy currency for metabolism. Almost all caloric content of food is converted into ATP before it can be utilized for tissue growth, muscle work and other physiological processes.

Axon
The cell extension of a neuron (nerve cell) that carries an electrical signal to synapses which are secreting chemical signaling molecules called neurotransmitters to stimulate/inhibit receiving cells. Some axons in the peripheral nervous system connecting to muscle cells or connecting sensory neurons from the skin, eye, or internal organs to the central nervous system can be quite long (measure in centimeters; 1 inch = 2.54 cm) compared to the size of an average cell (measured in micrometers).