Crossword clues for intercalation
intercalation
The Collaborative International Dictionary
Intercalation \In*ter`ca*la"tion\, n. [L. intercalatio: cf. F. intercalation.]
(Chron.) The insertion of a day, or other portion of time, in a calendar.
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The insertion or introduction of anything among others, as the insertion of a phrase, line, or verse in a metrical composition; specif. (Geol.), the intrusion of a bed or layer between other layers.
Intercalations of fresh-water species in some localities.
--Mantell.
Douglas Harper's Etymology Dictionary
1570s, from Latin intercalationem (nominative intercalatio) "insertion of an intercalary day," noun of action from past participle stem of intercalare (see intercalate).
Wiktionary
n. 1 A period inserted into a calendar as in a leap year. 2 (context chemistry English) The reversible insertion of a molecule between two others. 3 (context geology English) A layer introduced into a pre-existing sequence.
WordNet
n. an insertion into a calendar [syn: embolism]
Wikipedia
Intercalation or embolism in timekeeping is the insertion of a leap day, week, or month into some calendar years to make the calendar follow the seasons or moon phases. Lunisolar calendars may require intercalations of both days and months.
Intercalation, in the context of university administration, is a period when a student is officially suspended from studying for an academic degree.
When a university or similar institution allows a student to intercalate, it is usually for one of the following reasons:
- on medical or compassionate grounds, so that the student can take a break from his or her studies and return later
- to allow the student to gain work experience in a field related to his or her field of study
- for medical, dental and veterinary students in the UK, to allow the student to pursue a separate but related research degree (normally for one year) and then return to the main medical, dental or veterinary degree
Intercalation may refer to:
- Intercalation (biochemistry), insertion of a molecule into DNA between the bases
- Intercalation (chemistry), insertion of a molecule (or ion) into layered solids such as graphite
- Intercalation (timekeeping), insertion of a leap day, week or month into some calendar years to make the calendar follow the seasons
- Intercalation (university administration), period when a student is officially suspended from studying for an academic degree
- Intercalation (geology), a special form of interbedding, where two distinct depositional environments in close spatial proximity migrate back and forth across the border zone
- In biology:
- Intercalary segment, an appendage-less segment in the segmental composition of the heads of insects and Myriapoda
- Intercalation (biochemistry), process discovered by Leonard Lerman by which certain drugs and mutagens insert themselves between base pairs of DNA
- Intercalated cells of the amygdala
- Intercalated cells of the collecting duct
- Intercalated disc of cardiac muscle
- Intercalated duct of exocrine glands
In biochemistry, intercalation is the insertion of molecules between the planar bases of DNA. This process is used as a method for analyzing DNA and it is also the basis of certain kinds of poisoning.
There are several ways molecules (in this case, also known as ligands) can interact with DNA. Ligands may interact with DNA by covalently binding, electrostatically binding, or intercalating. Intercalation occurs when ligands of an appropriate size and chemical nature fit themselves in between base pairs of DNA. These ligands are mostly polycyclic, aromatic, and planar, and therefore often make good nucleic acid stains. Intensively studied DNA intercalators include berberine, ethidium bromide, proflavine, daunomycin, doxorubicin, and thalidomide. DNA intercalators are used in chemotherapeutic treatment to inhibit DNA replication in rapidly growing cancer cells. Examples include doxorubicin (adriamycin) and daunorubicin (both of which are used in treatment of Hodgkin's lymphoma), and dactinomycin (used in Wilm's tumour, Ewing's Sarcoma, rhabdomyosarcoma).
In order for an intercalator to fit between base pairs, the DNA must dynamically open a space between its base pairs by unwinding. The degree of unwinding varies depending on the intercalator; for example, ethidium cation (the ionic form of ethidium bromide found in aqueous solution) unwinds DNA by about 26°, whereas proflavine unwinds it by about 17°. This unwinding causes the base pairs to separate, or "rise", creating an opening of about 0.34 nm (3.4 Å). This unwinding induces local structural changes to the DNA strand, such as lengthening of the DNA strand or twisting of the base pairs. These structural modifications can lead to functional changes, often to the inhibition of transcription and replication and DNA repair processes, which makes intercalators potent mutagens. For this reason, DNA intercalators are often carcinogenic, such as the exo (but not the endo) 8,9 epoxide of aflatoxin B, acridines such as proflavine or quinacrine, or ethidium bromide.
Intercalation as a mechanism of interaction between cationic, planar, polycyclic aromatic systems of the correct size (on the order of a base pair) was first proposed by Leonard Lerman in 1961. One proposed mechanism of intercalation is as follows: In aqueous isotonic solution, the cationic intercalator is attracted electrostatically to the surface of the polyanionic DNA. The ligand displaces a sodium and/or magnesium cation present in the "condensation cloud" of such cations that surrounds DNA (to partially balance the sum of the negative charges carried by each phosphate oxygen), thus forming a weak electrostatic association with the outer surface of DNA. From this position, the ligand diffuses along the surface of the DNA and may slide into the hydrophobic environment found between two base pairs that may transiently "open" to form an intercalation site, allowing the ethidium to move away from the hydrophilic (aqueous) environment surrounding the DNA and into the intercalation site. The base pairs transiently form such openings due to energy absorbed during collisions with solvent molecules.
Usage examples of "intercalation".
According to the Gregorian rule of intercalation, therefore, every year of which the number is divisible by four without a remainder is a leap year, excepting the centurial years, which are only leap years when divisible by four after omitting the two ciphers.
Julian year was corrected in the Gregorian calendar by the suppression of three intercalations in 400 years.
In the Protestant states of Germany the Julian calendar was adhered to till the year 1700, when it was decreed by the diet of Regensburg that the new style and the Gregorian correction of the intercalation should be adopted.
Julian intercalation was now found to amount to three days in 400 years, he ordered the intercalations to be omitted on all the centenary years excepting those which are multiples of 400.
Most societies introduced extra months at certain times to overcome the discrepancy between the lunar and the solar year, but though such procedures often redressed the situation on a temporary basis, other intercalations, as they are called, were eventually needed.