Mirror Image Life: Building Reflections of our RNA
Background
Have you ever wished you were an identical twin? Imagine what you could do with a mirror image of yourself. Now imagine what could be done with mirror images of all life. Natural life has not been found in mirror image forms, but scientists are working on exploring if such a feat could be possible. This mirror image is accomplished through the concept of chirality.
Summary
Chirality
Chiral molecules are molecules that have a reverse image, but while the reverse image is made of the same atoms, and they have the same connectivity, (meaning the same atoms are connected) they have different configurations, so while a carbon may be bonded to four separate groups, say, a methyl group, a hydrogen, an oxygen and a bromine, there could be a switch of two of the atom positions, making them mirror image molecules but non-superimposable.
The same applies for larger molecules, but not for whole organisms. There are two different configurations, D (dexter)/ R (right, clockwise) and L (laevus) / S (left, counterclockwise). Natural-chirality amino acids tend to be in the L configuration, while nucleic acids tend to be in the D configuration. This study looked at making and using D-amino acids and L-nucleic acids, which would be the mirror image of the naturally occurring chirality.
Central Dogma
To make mirror image life, there would need to be a mirror image counterpart for each piece of the central dogma of biology, which says that DNA is replicated and then transcribed to RNA, and that transcript is then translated into proteins. To realize the central dogma, there must be a reflection to each process, including translation. Certain pieces of RNA called L-RNAs are used to make up RNA and ribosome components, but they have proven difficult to synthesize artificially because of their large size.
One way that L-RNA could be produced looks at making a new T7 RNA polymerase — one of the enzymes used to transcribe DNA from a template — and then make that polymerase synthesize the other pieces you need. But T7 RNA is still too big for the current limits of chemical synthesis, so scientists are using split protein design (splitting large proteins into smaller pieces that can fold together to interact as a complete enzyme) and isoleucine substitution, which switches leucine for a different amino acid.
The split protein design breaks the protein into three fragments: a 363-amino acid N fragment, a 282-amino acid C fragment, and a 238-amino acid M fragment that goes in the middle. Each of these fragments is further broken into five-eight peptide segments, and each of the peptide segments can contain anywhere from 20 to 76 amino acids.
Ribosomal RNA
After making each fragment, the fragments fold together to transcribe a double-stranded L-DNA sequence coding for Thermus thermophilus (bacteria) 5S RNA, which is the smaller component of the large ribosomal subunit. The large ribosomal subunit is where the peptidyl transferase reaction takes place to bond amino acids into protein chains. This mirror image 5S rRNA is able to resist attacks by ribonucleases within the cell that would digest the RNA, because the ribonucleases are not mirror images so they will not match up with the mirror image RNA. tRNAs are also able to be made in this manner, and they are also resistant to the nuclease digestion attempts.
This mirror image ribosome could be more beneficial to use in experiments than natural-chirality rRNAs because it is more stable due to its ability to not be degraded by ribonucleases. Several experiments were performed to compare the natural-chirality and mirror-image ribosomes, and the mirror-image rRNA performed substantially better. This could be helpful for experiments because an RNA with a long half-life will last longer in the cell and because of that be able to transcribe more protein. Tests confirmed that the rate of errors in the mirror-image ribosomes were similar to natural-chirality ribosomes, meaning that both pathways had relatively the same fidelity.
This mirror image ribosome could be more beneficial to use in experiments than natural-chirality rRNAs because it is more stable due to its ability to not be degraded by ribonucleases.
This study is important because it could allow further studies on ribosomes to investigate the origins of life, and in other applications such as therapeutics and medical treatments, the storage of information, as well as expanding the knowledge base of basic RNA research.
If you are interested in reading more research on this topic, you can find similar research in Biotechnology Advances.
Grove City College students can find any of these journals by simply searching the journal name in Discover on the Henry Buhl Library’s homepage. And don’t forget — if you’d like to find more related resources, the library maintains a list of A-Z Databases with an entire tab dedicated to biology!
