Non-translatable RNA: The Handyman of Easy Synthesis and Breakdown in Living Organisms

Differences between RNA and DNA

First, let’s explain what RNA is. There is a similar substance called DNA, but what are the differences between these two?

DNA stands for deoxyribonucleic acid, and RNA stands for ribonucleic acid. As the names suggest, their structures are different. DNA consists of adenine (A), guanine (G), thymine (T), and cytosine (C), while RNA contains uracil (U) instead of thymine.

What are the differences in their roles? The roles can be summarized as follows:

Thus, although their names and structures are similar, their roles in the body are quite different.

There are many types of RNA, each with different roles, which we will explain in detail.

Coding RNA that Codes for Proteins

Coding RNA, also known as translational RNA, refers to RNA that codes for proteins. Coding means that sets of three nucleotides specify an amino acid. In other words, RNA that carries genetic codes for producing amino acids is known as coding RNA.

For example, the RNA sequence AUG codes for methionine, and CCG codes for glycine. These amino acids link together to form proteins, which make up our bodies.

There is only one type of coding RNA: mRNA (messenger RNA).

mRNA (Messenger RNA)

As its name suggests, mRNA carries genetic information.

Based on the nucleotide chain in the nucleus, RNA polymerase synthesizes RNA that copies the genetic information from DNA. This RNA is called mRNA, and the process of copying genetic information is called transcription. Transcribed mRNA carries the genetic code in sets of three nucleotides (codons), which specify amino acids. This process of synthesizing proteins from mRNA is called translation.

It is known that only about 2% of the human genome is transcribed into mRNA. Therefore, only a small portion of the genome becomes protein. The functions of the remaining parts were not well understood until the late 1990s, when the discovery of microRNA (miRNA) revealed that various non-coding RNAs are synthesized from the non-protein-coding parts of the human genome and play essential roles in the body.

Non-Coding RNA for Various Uses

Non-coding RNA, or ncRNA, refers to RNA that does not have codons for proteins. As the name suggests, it does not code for proteins and functions without being translated.

Various non-coding RNAs have been discovered, including tRNA and rRNA.

tRNA (Transfer RNA)

tRNA, also known as transfer RNA, transports amino acids from the cytoplasm to the ribosome during protein synthesis. tRNA has complementary sequences to the codons on mRNA and binds to specific amino acids. By binding to codons on mRNA, tRNA translates the genetic code into amino acids, which are then linked by peptide bonds to form proteins.

rRNA (Ribosomal RNA)

Ribosomal RNA is abundant in cells and blood, existing on multiple chromosomes, and constitutes the ribosome along with proteins. During translation, rRNA decodes the codons on mRNA and binds complementary sequences on tRNA, playing a critical role in protein synthesis.

Due to its high expression, 18S rRNA is often used as an internal standard in genetic analysis. (S represents the sedimentation coefficient)

microRNA (miRNA)

MicroRNA is a short (21-25 nucleotides) single-stranded RNA. Since its discovery in 2001, it has been found to play a crucial role in regulating gene expression. It is also involved in many diseases, including cancer, neurological disorders, and vascular diseases, making it a key focus in biomarker and companion diagnostic development and personalized medicine.

Recent research has shown that miRNA within extracellular vesicles called exosomes is involved in cancer proliferation and metastasis, leading to new cancer diagnostic and therapeutic methods targeting exosomal miRNA.

Understanding and developing exosomal RNA could significantly advance early cancer detection and treatment.

lncRNA (Long Non-Coding RNA)

Long non-coding RNA refers to RNA longer than 200 nucleotides. Since the discovery of 6500 lncRNAs in 2009, active research has identified over 20,000 lncRNA genes and transcripts in humans, outnumbering human genes.

lncRNAs play essential roles in building nuclear structures and post-translational modifications. However, due to their low expression compared to mRNA, they are challenging to analyze, leaving much to be discovered. Nevertheless, research on lncRNAs is increasing.

lncRNAs are also involved in X chromosome inactivation.

In human females, the sex chromosomes are XX, while in males, they are XY. To balance the genetic dosage, one of the X chromosomes in females is inactivated, a mechanism involving lncRNA. When this inactivation does not function correctly, genetic disorders like Turner syndrome (missing X chromosome) and Klinefelter syndrome (extra X chromosome) can occur.

These are just a few examples of diseases related to lncRNA, with more research expected to develop new treatments for various conditions.

Other ncRNAs

Many other types of non-coding RNAs have been discovered.

snRNA (small nuclear RNA) is suggested to be involved in selective splicing and protection of mRNA precursors. Many human genetic diseases are caused by abnormalities in selective splicing regulation, and research on snRNA may contribute to understanding the causes of genetic diseases.

snoRNA (small nucleolar RNA) is involved in the synthesis of ribosomal RNA and the modification of nucleic acids. Located in the nucleolus of the cell nucleus, snoRNA is also part of telomerase, which synthesizes telomeres.

Other non-coding RNAs include SRP RNA (signal recognition particle RNA), used in nucleic acid medicine, siRNA, and piRNA, which protects genomic DNA in germ cells. Many non-coding RNAs are involved in diseases, but their low expression levels make them difficult to analyze, necessitating further research to clarify their mechanisms.

Summary

This article summarized the names and roles of various RNAs.

Non-coding RNAs do not code for genes or make proteins, making them easy to synthesize and degrade in the body. Because of this, they play many roles as versatile molecules in the body. Recent research has revealed that they are involved in various diseases, and understanding their mechanisms will help humanity overcome genetic diseases.

References

• Learning Genetics from Scratch, 2nd Edition, by Takaaki Tamura
• High School Biology, First Learning Company