The electromagnetic spectrum, broken by a specific pattern of dark lines or bands, which are observed when electromagnetic radiation traverses a particular absorbing medium. An absorption spectrum is, in a sense, the opposite of an emission spectrum.

Adenine (symbol A) is one of the constituent bases of DNA (and RNA), which pairs with thymine (and uracil).

In chemistry, alcohol is used as a more general term to signify any organic compound in which a hydroxyl group (OH) is bound to a carbon atom, which in turn is bound to other hydrogen and/or carbon atoms. The simplest and most commonly used alcohols are methanol and ethanol.

Any of a class of highly reactive chemical compounds containing a carbon atom linked to oxygen and a hydrogen atom. They are mainly used for the manufacture of synthetic resins,  dyestuffs, flavourings, perfumes, and other common chemicals.

Simple organic compounds, in which a carbon atom is connected to an oxygen and a nitrogen atom. Twenty amino acids serve as building blocks (basic units) of protein molecules. The arrangement of amino acids in a protein is called amino acid sequence. The shape and function of each protein are determined by the kind of amino acids involved in its making and their arrangement in its structure.

Fibrous and insoluble aggregates of misfolded proteins. Abnormal structures of amyloid proteins found in the brain are called amyloid plaques. The formation of amyloid plaques is thought to contribute to the degradation of brain neurons (nerve cells) and is linked to the emergence of degenerative diseases such as the Alzheimer's disease.

A type of protein. The body's immune system produces antibodies when it detects harmful substances, called antigens. Each type of antibody is unique and defends the body against one specific type of antigen.

A colorless, odorless, tasteless, nontoxic gaseous element constituting approximately one percent of the Earth's atmosphere. It remains inert under most conditions and forms no confirmed stable compounds at room temperature.

The mixture of gases and particles which cover the surface of the earth. This natural body of air is composed of approximately 21% oxygen, 78% nitrogen, and 1% other gases.

The presence in the air of one or more contaminants in such a  concentration and of such duration as to cause a nuisance or to be injurious to human life, animal life or vegetation.

The smallest particle of an element that can exist either alone or in combination, consisting of electrons, protons, and neutrons. Early theories on the composition of matter begin in 400 B.C., with the ancient Greek philosopher Democritus who thought matter could not be divided indefinitely.

The arrangement and number of smaller particles (protons, neutron, electrons) of an atom.

Time unit equal to one quintillionth of a second (10-18s) or one thousandth of a femtosecond.