Transfer RNA
From EvoWiki
| See Transfer RNA in Wikipedia, the free encyclopedia. |
Tranfer RNA (or tRNA) is a small ribose nucleic acid (RNA) important for protein translation.
Contents |
Structure
Primary Structure
For all organisms, tRNA molecules are a string of RNA ranging from 60 to 95 nucleotides in length, with the average at around 76. 15 of those nucleotides are invariant across all organisms and 8 are highly conserved.
Unlike most RNA, tRNA has a high concentration of non-typical nucleosides - that is, something other than adenosine (A), guanosine (G), cytidine (C) and uridine (U). There are around 80 different nucleosides in tRNA than most other RNAs, including thymidine (T), inosine (I), dihydrouridine (D) and pseudouridine (Ψ). These are found most often at the anticodon site and acceptor stem (see below), but also throughout the rest of the sequence.
Secondary Structure
The secondary structure of tRNA is often referred to as a cloverleaf, because without considering the tertiary structure, it can resemble the three 'loops' of a clover.
tRNA may be divided into two regions: "duplex" regions where part of the RNA strand binds to another part, becoming double-stranded, and "non-duplex" where no such binding occurs. It is the non-duplex regions that make up the 'loops' of the cloverleaf, with the non-duplex regions making up the 'stems'.
The combination of stems and loops create three complete 'arms':
- D arm, so named because its loop usually contains dihydrouridine.
- T arm, so named because its loop usually contains thymidine and pseudouridine.
- anticodon arm, which has a loop featuring the anticodon.
There is also another small section (3 bases, always CCA) of non-duplex RNA at the acceptor arm, which does not form a loop because the stem is made up of the two ends of the RNA strand. It is at this site that the amino acid corresponding to the anticodon attaches (forming an aminoacyl tRNA complex).
Tertiary Structure
In nature, the loops and stems of the various arms also interact with one another. The loops of the T arm and the D arm bind together, forcing the acceptor stem to bend in such a way that it is at a right angle to the anticodon arm. It is this shape, resembling a powerdrill, that allows for all tRNA molecules to bind to the ribosome during translation.
References
- Hartl, Daniel L. & Jones, Elizabeth W. (2005), Genetics: Analysis of genes and genomes Jones and Bartlett Publishers. 6th Edition, p431-2
|
This page is part of the EvoWiki encyclopedia of genetics and molecular biology. Topics: Genetics - Transmission genetics - Molecular genetics - Population genetics - Quantitative genetics - Molecular biology - Genomics |
