Glossary of Scientific Terms

E

Ecosystem
A specific characteristic biological system in a location or area with a unique mix of living organisms and physical consistency such as minerals, soil and air.

Electron
Subatomic particle carrying a negative electric charge in atoms or molecules.

Electrophysiology
The technique of recording and stimulating currents and voltages across cell membranes using microelectrodes. Electrodes can be used to measure membrane potentials and inject currents. The latter charges the membrane and changes the membrane potentials. If the recorded voltage change is fed back to the stimulating electrode, the current can be adjusted such that the measured membrane potential stays constant. This is called the 'voltage-clamp' technique and has largely been responsible to elucidate the mechanism underlying the electrical phenomena of neurons and muscle tissue.

Element
An atom with a unique number of protons (atomic number). There are 102 different elements and some additional synthetic elements that are not found in nature. Elements have different physical and chemical properties and can be combined to molecules (two or more atoms linked through covalent bonds). The elements are listed according to atomic number and chemical properties in the periodic table.

Embryonic Stem Cell
The pluripotent stem cells in animals at the very early embryonic development. They have the potential to grow into a complete adult organism.

Entropy
The energy form of a system that relates to its internal state of disorder. High entropy levels are disordered states, low entropy levels are characteristic of ordered states.

Enzyme
A protein (complex) that catalyzes a chemical reaction as part of a cell's metabolism. While many chemical reactions proceed spontaneously (although many don't), enzymes can increase the rate of these reactions by a thousand to a million fold. In addition to speeding up chemical reactions, enzymes are particularly good at selecting the correct molecules (substrate specificity) that can be used for a chemical reaction (e.g. extracting energy for the growth of an organism).

Equilibrium (chemical)
At equilibrium, the state of a system does not change over time, although internal fluctuation may exist. Thermodynamically, the equilibrium is the physical state of a system that has the lowest total energy content. To lower the energy content, a system may give up energy in form of heat or work or entropy, and usually it is a combination of all three. The laws of thermodynamic dictate that the total amount of energy cannot be changed and whatever energy in a system is lost, is taken up by the surroundings (the first law). The second law dictates that at equilibrium the entropy portion of the energy content of a system must be at its maximum. Interestingly, life is characterized by avoiding equilibrium states and minimizing entropy. This is used as an explanation of how life can maintain highly organized structures (minimal entropy) at the expense of the environment, whose entropy or disorder increases. Importantly, the energy content of a system and its surroundings are interdependent and the equilibrium state of a system can be changed by changing the internal composition or external conditions (e.g. rising temperature). This shift from one equilibrium (state 1) to a second equilibrium (state 2) is often characterized as chemical equilibrium describing the relationship between two states of a system that exist under slightly different conditions. Mathematically, the equilibrium can be described with the equilibrium constant where both states are equally probable. This constant allows the quantification of system properties such as the binding of a drug to its receptor protein.

Essential amino acid or fatty acid
An amino acid or fatty acid that cannot be synthesized by our own cells and need to be part of our diet to stay healthy.

Eukaryotes, Eukarya
Organisms with large cells and internal membrane bound structures called organelles. The defining organelle is the nucleus. Eukaryotes differ from prokaryotes. The latter have no nucleus or any organelle, usually a single naked chromosome (eukarya have several inside the nucleus) and are either bacteria or archaea.

Evolution, theory of
The theory of evolution as initially formulated by Charles Darwin in 1859 is the central theory of biology. All processes that enable life are the result of the process of evolution over a period estimated to be more than 3 billion years. The mechanism of evolution are mutation and natural selection. These two processes result in changes at the genetic (mutation) and physiological level (selection of function). 

Exon
An exon is a stretch of protein coding sequence in eukaryotic genes. Exons are interrupted by intron or intervening sequences. Introns are cut out at the mRNA level and the exons spliced together to form a complete, uninterrupted coding sequence. This matured mRNA is recognized by ribosomes and used as a template to synthesize a corresponding amino acid sequence or protein (see also intron).