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Word / termDefinition

zDNA

A left-handed form of DNA found under physiological conditions in short GC segments that are methylated.  It may be important in regulating gene expression in eukaryotes.

Zebra fish

The Zebra fish is one of many model organisms used in biomedical research to understand development of higher organisms, the functioning of nervous systems, and fundamental aspects of physiology and the cause of diseases.

Zero

The additive identity. The number that when you add it to a number, n, you will get n as a result.

Zero Standard

The zero standard is a baseline standard calibrator which contains no detectable concentration of the analyte being assayed. In competitive binding assays, the zero baseline standard is termed the Bzero. In sandwich assays, the zero standard is termed the zero blank.

Zinc finger

Configuration of a DNA-binding protein that resembles a finger with a base, usually cysteines and histidines, binding a zinc ion; A protein structural motif common in DNA binding proteins.Discovered in a transcription factor in Xenopus but present in a large number of different proteins.It is is found as part of transcription regulatory proteins. It is one of the most abundant DNA-binding motifs. Proteins may contain more than one finger in a single chain; each motif consists of 2 antiparallel beta-strands followed by by an alpha-helix. A single zinc ion is tetrahedrally coordinated by conserved histidine and cysteine residues, stabilising the motif. Four Cys residues are found for each "finger" and one finger can bind a molecule of zinc. A typical configuration is: CysXxxXxxCys--(intervening 12 or so aa's)—CysXxxXxxCys. Fingers bind to 3 base-pair subsites and specific contacts are mediated by amino acids in positions -1, 2, 3 and 6 relative to the start of the alpha-helix. Contacts mainly involve one strand of the DNA.
Where proteins contain multiple fingers, each finger binds to adjacent subsites within a larger DNA recognition site thus allowing a relatively simple motif to specifically bind to a wide range of DNA sequences.

Zona pellucida

A thick extracellular matrix surrounding the mammalian ovum (egg) which binds sperm and initiates the acrosome reaction of the sperm.

Zona reaction

In mammals, modification of the zona pellucida that blocks polyspermy; enzymes released by cortical granules digest sperm receptor proteins ZP2 and ZP3 so that they can no longer bind sperm.

Zooplankton

A collective term for the nonphotosynthetic organisms present in plankton.

Zwitterion

An ionic molecule with separate positive and negative charges, resulting in a net charge of zero.

Zygosis

The union of gametes to form a zygote; conjugation.

Zygote

The diploid product of the union of haploid gametes in conception; a fertilized egg, the fusion of a male and female gamete, containing two sets of chromosomes, one from the egg (oocyte) and one form the sperm. The product of gamete fusion. In organisms with a haploid life cycle, the zygote immediately undergoes meiosis, but in organisms with a multicellular diploid stage, the zygote is merely the first stage in the diploid portion of the life cycle. The unique diploid cell formed by the fusion of two haploid cells (often an egg and a sperm) that will divide mitotically to create a differentiated diploid organism.

Zymogens

The enzymatically inactive precursors of certain proteolytic enzymes.
The enzymes are inactive because they contain an extra piece of peptide chain. When this peptide is hydrolyzed (clipped away) by another proteolytic enzyme the zymogen is converted into the normal, active enzyme. The biochemical change usually occurs in a lysosome where a specific part of the precursor enzyme is cleaved in order to activate it. The amino acid chain that is released upon activation is called the activation peptide.The reason for the existence of zymogens may be to protect the cell, its machinery, and/or the place of manufacture within the cell from the potentially harmful or lethal effects of an active, proteolytic enzyme. In other words, the strategy is to activate the enzyme only when and especially where it is needed
Zymogens are sometimes referred to as proenzymes.

Zymurgy

Science of brewing beer. Also the last word in the dictionary.