Biomedical Engineering Reference
In-Depth Information
Mature mRNA is transported through the nuclear membrane to the cytoplasm where the translation
of mRNA to protein occurs with the aid of ribosomes. These ribosomes contain a variety of different
proteins and an assortment of RNA molecules, collectively known as ribosomal RNA (rRNA). These
short-lived but abundant rRNAs are involved in the binding of mRNA to the ribosome during the
translation process.
The translation of mRNA to protein is facilitated by transfer RNA (tRNA), which associates with the 20
common amino acids (there are 22 genetically encoded amino acids) and controls the sequential
binding of the amino acids according to the 3-letter base sequences (codons) on the mRNA. In this
way, the tRNA is responsible for positioning the correct amino acid residue at the ribosome, as
dictated by the base pair sequence in the mRNA.
Information is transmitted in transcription and translation processes through three-letter words and
an alphabet of four letters. Because there are 3 base sequences, there are 4
3
or 64 possible codons
(see
Figure 1-7
), 3 of which are used as stop codons, and 1 for the start codon, to mark the end and
start of translation, respectively. The remaining codons are used as redundant representations of the
amino acids. In most cases, the first two bases are fixed, and the redundancy occurs in the last base.
For example, the codons CCC, CCT, CCA, and CCG all code for the amino acid Proline.
Figure 1-7. RNA-Protein Codon Transcription Wheel. The 64 possible codons
