element


element
1. A substance composed of atoms of only one kind, i.e., of identical atomic (proton) number, that therefore cannot be decomposed into two or more elements and that can lose its chemical properties only by union with some other e. or by a nuclear reaction changing the proton number. 2. An indivisible structure or entity. 3. A functional entity, frequently exogenous, within a bacterium, such as an extrachromosomal e.. [L. elementum, a rudiment, beginning]
- actinide elements SYN: actinides.
- alkaline earth elements those elements in the family Be, Mg, Ca, Sr, Ba, and Ra, the hydroxides of which are highly ionized and hence alkaline in water solution.
- amphoteric e. an e., one or more of whose oxides unite with water to form hydroxides that may act as acids or as bases ( e.g., aluminum).
- anatomical e. any anatomical unit, such as a cell. SYN: morphologic e..
- copia elements a mobile genetic e. with retrovirus-like sequence organization.
- electronegative e. an e. whose atoms have a tendency to accept electrons and form negative ions ( e.g., oxygen, sulfur, chlorine).
- electropositive e. an e. whose atoms have a tendency to lose electrons and form positive ions ( e.g., sodium).
- fold-back elements a type of transposable e. that possesses long inverted repeat s, such that when denatured, loops are formed.
- labile elements tissue cells, as of epithelium, connective tissue, etc., that continue to multiply by mitosis during the life of the individual.
- long interspersed elements (LINES) long repetitive sequences in DNA with terminal repeats seen in human and mouse DNA.
- morphologic e. SYN: anatomical e..
- neutral e. an e. of the zero group of the periodic system comprising the noble gases, He, Ne, Ar, Kr, Xe, Rn.
- noble e. SYN: noble metal.
- P elements a class of transposable elements in Drosophila responsible for hybrid dysgenesis; utilized as tools for introducing genes into new locations in the genome.
- picture e. pixel.
- rare earth elements SYN: lanthanides.
- short interspersed elements (SINES) highly repetitive sequences of DNA of about 300 base pairs in length that occur about every 3000–5000 bp in the genome.
- trace elements elements present in minute amounts in the body, many of which are essential in metabolism or for the manufacture of essential compounds; e.g., Zn, Se, V, Ni, Mg, Mn. SYN: microelements, microminerals.
- transposable e. a DNA sequence that can move from one location in the genome to another; the transposition event can involve both recombination and replication, producing two copies of the moving piece of DNA; the insertion of these DNA fragments can disrupt the integrity of the target gene, possibly causing activation of dormant genes, deletions, inversions, and a variety of chromosomal aberrations. SEE ALSO: transposon.

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el·e·ment 'el-ə-mənt n
1) any of the four substances air, water, fire, and earth formerly believed to compose the physical universe
2) a constituent part: as
a) any of more than 100 fundamental substances that consist of atoms of only one kind and that singly or in combination constitute all matter
b) one of the distinct parts (as a lens) of a composite device (as a microscope)
c) one of the basic constituent units (as a cell or fiber) of a tissue

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el·e·ment (elґə-mənt) [L. elementum] 1. any of the constituent parts of which a more complex entity is composed. 2. in chemistry, a simple substance which cannot be decomposed by chemical means and which is made up of atoms which are alike in their peripheral electronic configurations and so in their chemical properties, and also in the number of protons in their nuclei, but which may differ in the number of neutrons in their nuclei and so in their atomic weight and in their radioactive properties. See Appendix 5. 3. in the philosophies underlying some complementary medicine systems, a member of a group of basic substances that give rise to everything that exists; see five e's.

Medical dictionary. 2011.

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