. Messenger RNA (mRNA) is
synthesized from a gene segment of DNA which ultimately contains the
information on the primary sequence of amino acids in a protein to be
synthesized. The genetic code as translated is for m-RNA not DNA.
The messenger RNA carries the code into the cytoplasm where protein
synthesis occurs. The cell does
not contain large quantities of mRNA. This is because mRNA, unlike other RNAs
is constantly undergoing breakdown.
- In
the cytoplasm, ribsomal RNA (rRNA) and protein combine to form a
nucleoprotein called a ribosome. The ribosome serves as the site and
carries the enzymes necessary for protein synthesis. The ribosome attaches
itself to m-RNA and provides the stabilizing structure to hold all substances
in position as the protein is synthesized. Several ribosomes may be attached to
a single RNA at any time.
- Transfer
RNA (tRNA) contains about 75 nucleotides, three of which are called
anticodons, and one amino acid. The tRNA reads the code and carries the
amino acid to be incorporated into the developing protein. Part of the
tRNA doubles back upon itself to form several double helical sections. The
tRNA "reads" the mRNA codon by using its own anticodon. The actual
"reading" is done by matching the base pairs through hydrogen bonding
following the base pairing principle. Each codon is "read" by various
tRNA's until the appropriate match of the anticodon with the codon occurs.
