| nonreciprocal contact inhibition | <cell biology> Collision behaviour between different cell types in which one cell shows contact inhibition of locomotion and the other does not. An example is the interaction between sarcoma cells and fibroblasts (the former not being inhibited). (18 Nov 1997) |
|---|---|
| nonrefractive accommodative esotropia | That type of esotropia in which an abnormality of the accommodative-convergence mechanism is not eliminated by correction of refractive error. (05 Mar 2000) |
| nonreset nodus sinuatrialis | Nonreset of the sinoatrial node produced by a premature atrial depolarisaton when the sum of the duration of the premature cycle and the return cycle is fully compensatory, i.e., twice the duration of the spontaneous cycle length. Compare: reset nodus sinuatrialis. (05 Mar 2000) |
| nonresponder tolerance | Lack of immune response to antigen. Theories of tolerance induction include clonal deletion and clonal anergy. In clonal deletion, the actual clone of cells is eliminated whereas in clonal anergy the cells are present but nonfunctional. Synonym: immunological tolerance, immunotolerance, nonresponder tolerance. (05 Mar 2000) |
| nonrotation | Failure of normal rotation. (05 Mar 2000) |
| nonrotation of intestine | A developmental anomaly resulting in the small intestine being on the right of the abdomen and the colon on the left. (05 Mar 2000) |
| nonrotation of kidney | A developmental anomaly in which the hilum of the kidney retains its original position, facing ventrally. (05 Mar 2000) |
| nonsaponifiable | Not subject to saponification; e.g., triacylglycerols are saponifiable but cholesterol is nonsaponifiable. (05 Mar 2000) |
| nonsecretor | An individual whose saliva does not contain antigens of the ABO blood group. See: secretor. (05 Mar 2000) |
| nonseminoma | A classification of testicular cancers that arise in specialised sex cells called germ cells. Nonseminomas include embryonal carcinoma, teratoma, choriocarcinoma, and yolk sac tumour. (12 Dec 1998) |
| nonsense | As used in genetics, relating to a mutation that causes a sequence such that the growing peptide chain terminates, often after several incorrect amino acid residues are incorporated. (05 Mar 2000) |
| nonsense codon | <molecular biology> The three codons, UAA (known as ochre), UAG (amber) and UGA (opal), that do not code for an amino acid but act as signals for the termination of protein synthesis. Any mutation that causes a base change which produces a nonsense codon results in premature termination of protein synthesis and probably a nonfunctional or nonsense protein. (13 Nov 1997) |
| nonsense mutation | <molecular biology> A mutation that causes a polypeptide chain to be ended prematurely. (13 Nov 1997) |
| nonsense strand | <molecular biology> DNA that does not code for part of a polypeptide chain or RNA.This includes introns and pseudo genes. In eukaryotes the majority of the DNA is noncoding. Noncoding strand refers to the so called nonsense strand, as opposed to the sense strand which is actually translated into mRNA. (18 Nov 1997) |
| nonsense suppression | Mutant tRNAs that read a chain termination codon as the signal for incorporation of a specific amino acid residue. (05 Mar 2000) |