Structure of RNA
RNA is normally a biopolymer with a single strand. The ribonucleotide chain is folded into complex structural forms with bulges and helices as a result of intrachain base-pairing and the presence of self-complementary sequences in the RNA strand. As a result of the ribose sugar and nitrogenous bases’ ability to be modified in a variety of ways by cellular enzymes that attach chemical groups (such as methyl groups) to the chain, the three-dimensional structure of RNA is essential to its stability and function.
These alterations make it possible for chemical connections to develop between far-flung areas of the RNA strand, resulting in intricate twists in the RNA chain that further stabilize the RNA structure. Molecules with weak structural modifications and stabilization may be readily destroyed. As an illustration, alteration at position 58 of the tRNA chain in an initiator transfer RNA (tRNA) molecule that lacks a methyl group (tRNAiMet) causes the molecule to become unstable and hence nonfunctional; the nonfunctional chain is then eliminated by cellular tRNA quality control mechanisms.
Additionally, RNAs can join forces with ribonucleoproteins to create complexes (RNPs). It has been demonstrated that the RNA part of at least one cellular RNP serves as a biological catalyst, a role formerly ascribed only for proteins.
Types and Functions of RNA
All organisms include messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA), which are the three most well-known and frequently studied kinds of RNA. Similar to enzymes, this and other varieties of RNA largely carry out biochemical processes. However, some also play intricate regulatory roles in cells. RNAs have significant roles in both healthy cellular processes and diseases due to their engagement in several regulatory processes, their quantity, and their variety of functions.
In the process of making proteins, mRNA transports genetic information from the nucleus’s DNA to the cytoplasm’s ribosomes, which carry out protein translation. rRNA and protein combine to form ribosomes. The ribosomal protein subunits are produced in the nucleolus and are encoded by rRNA. When fully constructed, they travel to the cytoplasm where, in their capacity as important regulators of translation, they “read” the information contained in mRNA.
A certain amino acid must be included in the sequence of bases that make up the protein, according to a pattern of three nitrogenous bases in mRNA. Less than 100 nucleotide long tRNA molecules, also known as soluble or activator RNA, transport the required amino acids to the ribosomes, where they are joined to generate proteins.
RNAs can be generically categorized into coding (cRNA) and noncoding (ncRNA) in addition to mRNA, tRNA, and rRNA . Housekeeping ncRNAs (tRNA and rRNA) and regulatory ncRNAs are two different types of ncRNAs that are further divided into groups based on their size. Small ncRNAs have fewer than 200 nucleotides, whereas long ncRNAs (lncRNA) have at least 200 nucleotides. Small ncRNAs are subdivided into micro RNA (miRNA), small nucleolar RNA (snoRNA), small nuclear RNA (snRNA), small-interfering RNA (siRNA), and PIWI-interacting RNA (piRNA).
The miRNAs are very significant. Most eukaryotes use these 22 nucleotide long proteins to regulate gene expression. By attaching to the target mRNA and limiting translation, they can suppress (silent) gene expression and stop the production of useful proteins. Numerous miRNAs have a big impact on cancer and other disorders. For instance, specific target genes can be regulated by tumor suppressor and oncogenic (cancer-initiating) miRNAs, resulting in carcinogenesis and tumor growth.
The piRNAs, which are often found in animals and range in length from 26 to 31 nucleotides, are also of functional importance. By preventing the genes from being transcribed in the germ cells(sperm and eggs), they control the expression of transposons (jumping genes). Most piRNA can target particular transposons since they are complementary to various transposons.
Since its 5′ and 3′ ends are linked by a loop, circular RNA (circRNA) differs from other RNA forms. Many protein-coding genes produce circRNAs, some of which can act as mRNA-like templates for protein synthesis. They have the capacity to bind miRNA, serving as “sponges” to stop miRNA molecules from attaching to their intended destinations. CircRNAs also have a significant impact on the transcription and alternative splicing of the genes from which they were generated.
RNA and Diseases
RNA and human disease have been linked in significant ways. For instance, as was previously mentioned, some miRNAs have the ability to regulate cancer-related genes in ways that promote the formation of tumors. In addition, a number of neurological disorders, including Alzheimer’s disease, have been related to deregulation of miRNA metabolism.
In the case of other RNA types, tRNAs can bind to specialized proteins known as caspases, which are involved in apoptosis (programmed cell death). The ability of cells to resist programmed death signaling is a distinguishing feature of cancer, and tRNAs prevent apoptosis by attaching to caspase proteins. Cancer-related tRNA-derived fragments (tRFs), commonly known as noncoding RNAs, may also be involved.
New classes of tumor-specific RNA transcripts have been discovered as a result of the development of techniques like RNA sequencing, including MALAT1 (metastasis associated lung adenocarcinoma transcript 1), whose elevated levels have been discovered in a variety of cancerous tissues and are linked to the proliferation and metastasis (spread) of tumor cells.
A class of RNAs containing repeat sequences is known to sequester RNA-binding proteins (RBPs), resulting in the formation of foci or aggregates in neural tissues. These aggregates contribute to the emergence of neurological disorders such myotonic dystrophy and amyotrophic lateral sclerosis (ALS). Numerous human disorders have been linked to various RBPs’ loss of function, dysregulation, and mutation.
It is anticipated that further RNA-disease connections will be found. Such findings are anticipated to be facilitated by improved knowledge of RNA and its activities, as well as by the continuous advancement of sequencing technologies and initiatives to screen RNA and RBPs as therapeutic targets.