electromagnetic radiation
Range of energy-containing wavelengths, including radio waves, infrared radiation, visible light, UV light, and X-rays.

Electron transfer chain
The electron transfer chain, also called the electron transport chain, is a sequence of complexes found in the mitochondrial membrane that accept electrons from electron donors such as NADH or succinate, shuttle these electrons across the mitochondrial membrane creating an electrical and chemical gradient, and, through the proton driven chemistry of the ATP synthase, generate adenosine triphosphate.

There are five complexes normally associated with the electron transfer chain.

• Complex I - NADH dehydrogenase, also called NADH Coenzyme Q reductase.

• Complex II - Succinate - Coenzyme Q reductase.

• Complex III - Coenzyme Q - cytochrome c reductase.

• Complex IV - Cytochrome c oxidase.

• Complex V - ATP Synthase, also known as the F0F1 particle.

Complexes I, III, and IV are proton pumps. Complex II is part of the Krebs cycle and does not pump protons, and Complex V uses the electrochemical potential generated to create ATP. Complex IV is the terminus of the electron transfer chain, consuming oxygen and making water.

• Cytochrome c

Cytochrome c is also an essential part of the electron transfer chain. It is a soluble protein loosely associated with the inner mitochondrial membrane, and transfers electrons between Complexes III and IV.

endocytosis
Endocytosis refers to a biological process whereby cells absorb material outside their cell membranes. Endocytosis is the opposite of exocytosis, and always involves the formation of a vesicle from part of the cell membrane. Endocytosis can be of three forms:

1. Pinocytosis (literally, cell drinking) is the invagination of the cell membrane to form a pocket filled with extracellular fluid. The pocket then pinches off to form a vesicle, and the vesicle ruptures to release its contents into the cytosol.

2. Receptor-mediated endocytosis is similar to pinocytosis, except it is prompted by the binding of a large extracellular molecule - such as a protein - to a receptor on the cell membrane. The invagination that results engulfs the protein, which is then released into the cytosol.

3. Phagocytosis is the process by which cells ingest large objects, such as prey cells or large chunks of dead organic matter. These are sealed off into large vacuoles. Lysosomes then merge with the vacuole, turning it into a digestive chamber. The products of the digestion are then released into the cytosol. Macrophages are cells of the immune system that specialize in the destruction of bacteria by phagocytosis.

enzyme
Proteins (usually) that catalyze specific biochemical reactions.

An enzyme is a special protein molecule whose function is to facilitate or otherwise accelerate most chemical reactions in cells. Many chemical reactions occur within biological cells, but without catalysts most of them happen too slowly in the test tube to be biologically relevant.  Enzymes can also serve to couple two or more reactions together, so that a thermodynamically favorable reaction can be used to "drive" a thermodynamically unfavorable one. One of the most common examples is enzymes which use the dephosphorylation of ATP to drive some otherwise unrelated chemical reaction.

epistasis
A genetic interaction whereby the expression of one gene affects the phenotypic expression of another gene.

equilibrium
A state at which the forward and reverse reactions are proceeding at equal rates.

eukaryotic
Organisms with membrane-bound nuclei and organelles; comprise the protist, plant, fungi, and animal kingdoms.

evolution
A change in the genetic structure of a population; gradual changes that occur in the characteristics of a species.

exocytosis
Exocytosis is the process of a biological cell releasing substances into the extracellular fluid (its environment). Exocytosis is the opposite of endocytosis.

exon
In eukaryotic DNA, a portion of a gene that codes for a polypeptide.