Messenger RNA is synthesized in the cell nucleus. Portions of a DNA molecule unwind, and the two strands separate. RNA nucleotides pair with complementary bases on a DNA strand, forming a strand of messenger RNA that is complementary to the DNA strand.
The DNA serves as a template, or pattern, for the synthesis of messenger RNA. In this way, the hereditary information in the nucleotide sequence of DNA is copied in complementary form into the nucleotide sequence of messenger RNA.
The sequence of nucleotides in messenger RNA contains the genetic code, which determines the amino acid sequence of proteins. The genetic code for each amino acid is a specific sequence of three nucleotides. The three-nucleotide sequence in messenger RNA that specifies a particular amino acid is called a codon.
Transfer RNA molecules are found in the cytoplasm. Their function is to carry amino acid molecules to the ribosomes, the sites of protein synthesis. There are 20 different kinds of amino acids in cells, and there is a different form of transfer RNA for each amino acid. Each kind of transfer RNA has a three-nucleotide sequence, called an anticodon, that is complementary to a codon on the messenger RNA.
The origin of ribosomal RNA is in the nucleolus. Ribosomal RNA is found in the ribosomes, which are the sites of protein synthesis. A functional ribosome is formed by two subunits, and each subunit is formed from RNA and associated proteins.
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Last modified July 30th 1997