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a Related Biological Terms:

F;rster transfer

(= resonance energy transfer)

Fourier transform infrared spectroscopy (FT-IR)

The special case of the application to the infrared spectrum (10-6-10-4 m) of interference optics. To avoid the disadvantage of dispersion/slit optics (the use of a prism or grating to separate polychromatic light into a spectrum and the exclusion of all the light except that of the desired wavelength), which utilizes only a very small fraction of the incident light, interference optics is used to decompose the absorption of polychromatic light. White light is split into two beams when it strikes a semi-transparent mirror; a system of mirrors rejoins the two beams at a detector. The pathlength of one beam may be adjusted by use of a moveable mirror so that this beam of light constructively interferes with, or re-enforces, the other when the two paths are exactly equal, or differ by an exact multiple of the wavelength; or it destructively interferes with it when the two paths differs by an exact multiple plus half the wavelength. The device, therefore, acts as a very narrow bandpass filter. When, under destructive interference conditions, a sample is introduced into one of the beams, the appearance of light at the detector is proportional to the absorbance of light at the selected wavelength by the sample. The intensity of energy at the detector is monitored as the pathlength is continuously varied over an informative range (800-4000 cm-1). The technique has been adapted to microscopic samples to obtain information on protein secondary structure.Lewis, E.N., Treado, P.J., Reeder, R.C., Story, G.M., Dowrey, A.E., Marcott, C., Levin, I.W. (1995) Anal. Chem. 67, 3377-3381; Lester, D.S., Kidder, L.H., Levin, I.W. and Lewis, E.N. (1998) Cell. Mol. Biol. 44 29-38 Learn more about amino acid chart.

Fourier transform-mass spectrometry (FT-MS)

A variant of mass spectrometry in which a molecular ion is stabilized in a cyclotron orbit and detected by the frequency of its oscillation. The consequent long half-life and non-destructive detection account for the high sensitivity of the method. (see also mass spectrometry (MS))

Fourier transformation

An analysis based on Fourier's theorem that any periodic function may be reduced to a series of sine and cosine terms, each represented by an amplitude and a phase. The transformation is the CASTing of data for a periodic phenomenon into such an alternative form, or the reconstruction of the phenomenon from its mathematical expression, e.g. reconstruction of a molecular model of a compound from an analysis of the X-ray diffraction pattern of its crystal, which is a three-dimensional periodic structure. (see also phase problem) Related tool: molecular biology tools

French paradox

The hypothesis that the lower incidence of heart disease in Mediterranean countries is due to ingestion of constituents of red wine, possibly flavinoids, that act to inhibit oxidation of low-density lipoproteins. Leake, D. (1995) The Biochemist 17 (1), 12-15

Fresco-Alberts-Doty model

(= hairpin loop (Fresco-Alberts-Doty model))

Fuelgen reaction

A qualitative colorimetric method for identification of DNA, especially in cytochemistry; treatment with fuchsin sulphurous acid to produce a red colour.

facilitated diffusion

A transport mechanism that moves compounds or ions down a concentration gradient, and requires no energy; also known as accelerated diffusion or mediated transport. (see also active transport; passive diffusion)

factitious protein

A product of genetic engineering; a protein designed for a specific purpose or for its expected properties.

fast-atom bombardment (FAB) mapping

A technique for comparison of recombinant with natural proteins or with expected structures. A protein is cleaved by a specific enzymic (e.g. trypsin) or chemical (e.g. CNBr) method and the product is characterized by FAB mass spectrometry. (see also fast-atom bombardment mass spectrometry (FAB-MS))

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