Two usages: In eukaryotes

A strand of RNA synthesized in-vitro

(the 5' end of one strand pairs with the 3' end of the opposite strand).

A nucleic acid strand is inherently directional, and the "5 prime end" has a free hydroxyl (or phosphate) on a 5' carbon and the "3 prime end" has a free hydroxyl (or phosphate) on a 3' carbon (carbon atoms in the sugar ring are numbered from 1' to 5'; see Figure 1

A region of DNA which is NOT copied into the mature mRNA, but which is present adjacent to 3' end of the gene (see Figure 4

A region of the DNA which IS transcribed into mRNA and becomes the 3' end or the message, but which does not contain protein coding sequence. Everything between the stop codon and the polyA tail is considered to be 3' untranslated (see Figure 4

A region of DNA which is NOT transcribed into RNA, but rather is adjacent to 5' end of the gene (see Figure 4

A region of a gene which IS transcribed into mRNA, becoming the 5' end of the message, but which does not contain protein coding sequence. The 5'-untranslated region is the portion of the DNA starting from the cap site and extending to the base just before the ATG translation initiation codon (see Figure 4

An experiment designed to produce an animal deficient in one or a few cell types, in order to study cell lineage or cell function. The idea is to make a transgenic mouse with a toxin gene (often diphtheria toxin) under control of a specialized promoter which activates only in the target cell type. When embryo development progresses to the point whe [..]

A polymer gel used for electrophoresis of DNA or protein to measure their sizes (in daltons for proteins, or in base pairs for DNA). See "Gel Electrophoresis". Acrylamide gels are especially useful for high resolution separations of DNA in the range of tens to hundreds of nucleotides in length.