| fick's law of diffusion | The principle that a substance put into solution will tend to diffuse towards constant concentration throughout the solution. (09 Oct 1997) |
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| Fick's laws of diffusion | The direction of movement of solutes by diffusion is always from a higher to a lower concentration and the diffusive flux JA of solute A across a plane at x is proportional to the concentration gradient of A at x; i.e., JA = -D(CA/x), the increase of concentration of solute A with time, CA/t, is directly proportional to the change in the concentration gradient, i.e., CA/t = D(fl2/x2). (05 Mar 2000) |
| lateral diffusion | Diffusion in two dimensions, usually referring to movement in the plane of the membrane, such as the motion of fluorescently labelled lipids or proteins measured by the technique of fluorescent recovery after photobleaching (FRAP). (18 Nov 1997) |
| least diffusion circle | In the configuration of rays emerging from a spherocylindrical lens system, the place where diverging rays of the lens first forming a line image are balanced by converging rays of the second lens. (05 Mar 2000) |
| agar-gel reaction | <immunology> The reaction between an antibody and an antigen during an immunology lab procedure where the two are allowed to diffuse toward each other through an agar-gel medium. Lines of precipitation form in the places on the gel where the two react with each other and shows where the reaction has occurred. (09 Oct 1997) |
| agarose gel electrophoresis | <procedure> A type of electrophoresis that uses a matrix of highly purified agar to separate large nucleotides in size. (06 May 1997) |
| aluminum hydroxide gel | A suspension containing Al2O3, mainly in the form of aluminum hydroxide, used as an antacid; a dried form, with the same use, is obtained by drying the product of interaction in aqueous solution of an aluminum salt with ammonium or sodium carbonate. (05 Mar 2000) |
| aluminum phosphate gel | An aqueous suspension of between 4.0 and 5.0% of aluminum phosphate; used as an antacid. (05 Mar 2000) |
| bag-gel implant | An implant composed of a silicone rubber bag containing a silicone gel; used in augmentation mammaplasty. (05 Mar 2000) |
| gel | Jelly like material formed by the coagulation of a colloidal liquid. Many gels have a fibrous matrix and fluid filled interstices: gels are viscoelastic rather than simply viscous and can resist some mechanical stress without deformation. Examples are the gels formed by large molecules such as collagen (and gelatin), agarose, acrylamide and starch. (18 Nov 1997) |
| gel electrophoresis | <molecular biology> Electrophoresis using a gel supporting phase. Usually applied to systems where the gel is based on polyacrylamide. See: electrophoresis. (05 May 1997) |
| gel exclusion chromatography | <investigation> A lab technique, a type of column chromatography, used to separate the components of a mixture by molecular size and to collect the molecules which are larger than a certain size. It is similar to gel filtration, small molecules are slowed or trapped by the pores in the gel beads filling the column, while large molecules, too large to fit into the pores, slide past the beads and get to the bottom of the column first. at this point, the large molecules are collected. Gel exclusion refers to the maximum size of molecule which will fit into the gel bead pores, and this lab technique is used to collect the molecules in the mixture which are larger than, or excluded from, the pores. (09 Oct 1997) |
| gel filtration | <molecular biology> An important method for separating molecules according to molecular size by percolating the solution through beads of solvent permeated polymer that has pores of similar size to the solvent molecules. Unlike a continous filter that retards flow according to molecular size, separation is achieved because molecules that can enter the beads take a longer path (i.e. Are retarded) than those that cannot. Typical gels for protein separation are made from polyacrylamide or from flexible (Sephadex) or rigid (agarose, Sepharose) sugar polymers. The size separation range is determined by the degree of cross linking of the gel. (05 May 1997) |
| gel filtration chromatography | See: gel filtration. (05 Mar 2000) |
| gel retardation assay | A lab technique used to find out if there are proteins binding a fragment of DNA (in a DNA-protein complex) by watching how fast the DNA fragment moves through an electric field and seeing whether it moves slower when a particular protein is also present. (09 Oct 1997) |