Hypermedia Glossary Of Genetic Terms
|Genetic code||The sequence of nucleotides, coded in triplets (codons) along the mRNA, that determines the sequence of amino acids in protein synthesis. The DNA sequence of a gene can be used to predict the mRNA sequence, and the genetic code can in turn be used to predict the amino acid sequence.|
|Nucleotide||A subunit of DNA or RNA consisting of a nitrogenous base (purine in adenine and guanine, pyrimidine in thymine, or cytosine for DNA and uracil cytosine for RNA), a phosphate molecule, and a sugar molecule (deoxyribose in DNA and ribose in RNA). Depending on the sugar the nucleotides are called deoxyribonucleotides or ribonucleotides. Thousands of nucleotides are linked to form a DNA or RNA molecule. See also base pair.|
|Codon||The term proposed by Crick (1963) for the sequence of nucleotides in DNA or RNA.which is responsible for determining that a specific amino acid shall be inserted into a polypeptide chain. There is more than one codon for most amino acids. It has now been established that the codon is a triplet of nitrogenous bases in DNA or RNA that specifies a single amino acid. See genetic code.|
|Messenger RNA (mRNA)||RNA that serves as a template for protein synthesis or for synthesis of cDNA. See genetic code.|
|Amino acid||Any of a class of 20 molecules that are combined to form proteins in living things. The sequence of amino acids in a protein and hence protein function are determined by the genetic code.
Amino acids contain a basic amino (NH2) group, an acidic carboxyl (COOH) group and a side chain (R - of a number of different kinds) attached to an alpha carbon atom.
Thus the general formula is:
|Protein||A large molecule composed of one or more chains of amino acids in a specific order; the order is determined by the base sequence of nucleotides in the gene coding for the protein. Proteins are required for the structure, function, and regulation of the bodys cells, tissues, and organs, and each protein has unique functions. Examples are hormones, enzymes, and antibodies.|
|Deoxyribonucleic acid (DNA)||The molecule that encodes genetic information. DNA is a double-stranded molecule held together by weak bonds between base pairs of nucleotides. The four nucleotides in DNA contain the bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In nature, base pairs form only between A and T and between G and C; thus the base sequence of each single strand can be deduced from that of its partner.|
|DNA sequence||The relative order of base pairs, whether in a fragment of DNA, a gene, a chromosome, or an entire genome. See base sequence.|
|Gene||The term coined by Johannsen (1909) for the fundamental physical and functional unit of heredity. The word gene was derived from De Vries' term pangen, itself a derivative of the word pangenesis which Darwin (1868) had coined. A gene is an ordered sequence of nucleotides located in a particular position (locus) on a particular chromosome that encodes a specific functional product (the gene product, i.e. a protein or RNA molecule). It includes regions involved in regulation of expression and regions that code for a specific functional product. See gene expression, allele.|
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