RNA: Definition, Structure, Types, Functions, Examples

What Is RNA?

Ribonucleic acid or RNA is one of the most important biomolecules functioning in the biological universe as the carrier of genetic information and involved in the process of genetic coding, decoding, regulation, and manifestation. Unlike DNA which keeps the information for the more extended future, RNA is involved in more dynamic functions in the cell.

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It is single-stranded and exists in different types among them include the messenger RNA (mRNA), the transfer RNA (tRNA) and the ribosomal RNA (rRNA) all of which play different vital roles in the synthesis of proteins and other major biological processes. Unlike DNA, RNA is not as stable and is principally located in the cytoplasm of eukaryotic cells; however, the primary purpose of RNA is to be directly involved in the actual process of translation or the process of building proteins using the code contained inside the DNA. Such versatility supports the significance of RNA within the gene expression and regulation process, thereby reaffirming RNA’s role as a critical component of any organism.

Structure Of RNA

The structure of RNA is discussed below:

• RNA is a polymer made up of nucleotides, each consisting of three components: consist of ribose sugar, a phosphate group, and a nitrogenous base.

• RNA has ribose as its sugar, this sugar has a hydroxyl group (OH) at the 2’ carbon of the sugar making RNA more reactive and less stable than DNA.

• The phosphate group links the 3’ carbon of one ribose sugar to the 5’ carbon of the next through a phosphodiester bond thus forming a backbone that is a sugar-phosphate linkage chain.

Types Of Nitrogenous Bases In RNA

• Adenine (A): One of the nitrogenous bases, which, in the transcription and translation process, combines with uracil (U). It is a double-ringed structure in nature.

• Uracil (U): A pyrimidine base that substitutes thymine in DNA, forming a pair with adenine (A). It is a single-ring structure and occurs only in RNA.

• Cytosine (C): One of the four nitrogenous pyrimidine bases which complement guanine (G). It has only a single ring and it is involved in the maintenance of stability of different structures of RNA.

• Guanine (G): One of the two purines that is complemented with cytosine (C). It has a double-ring structure and is utilised for the formation of stable RNA secondary structures.

Diagrams Illustrating RNA Structure

Types Of RNA

The types of RNA are discussed below:

Messenger RNA (mRNA)

mRNA helps in translating DNA for protein synthesis and it acts as the bridge between DNA and protein synthesis. It drags messages copied from nuclear DNA to the ribosomal RNA in the cytoplasm. In translation, the ribosomes therefore ‘read’ the mRNA sequence to make proteins in the order the letters of the genetic code were presented to them.

Transfer RNA (tRNA)

tRNA is highly essential in converting the four-lettered code from the mRNA into the twenty-lettered amino acids which make up proteins. Every tRNA molecule is tied with one particular amino acid and has its anticodon with the mRNA codons during protein synthesis. This helps in the correct positioning of the amino acids in the forming protein.

Diagram of tRNA structure

Ribosomal RNA (rRNA)

rRNA is an integral part of the organisation of ribosomes which is associated with the process of protein synthesis. It assists in the pairing of mRNA and tRNA and speeds up the linking of amino acids with peptide bonds. rRNA plays a role wherein it provides support and structural stability to the ribosome and also has a role in the functionality of this biological structure.

Other Types Of RNA

miRNA and siRNA issue selected mRNA particles, and they are considered to be implicated in gene silencing processes. snRNA or small nucleolar RNA That is engaged in posttranscriptional processing of mRNA, which includes RNA splicing. These specialized RNAs play a role in post-transcriptional regulation of genes and other cellular metabolism.

RNA Functions

The functions of RNA are discussed below:

Messenger RNA (mRNA)

• Role: Copies the genetic information from DNA to ribosome.

• Function: Serves as the blueprint on how proteins will be made by ensuring the right order of amino acids in the proteins.

Transfer RNA (tRNA)

• Role: Carries specific amino acids to the ribosome during the process of synthesis of proteins.

• Function: Has three parts an anticodon that base pairs with the codons on the mRNA bringing in the correct amino acid for the polypeptide’s formation.

Ribosomal RNA (rRNA)

• Role: Large or small subunit of the ribosomes.

• Function: Synthesises amino acids into proteins by fuelling the location where the mRNA and tRNA come together to translate the code.

Other Types Of RNA

• MicroRNA (miRNA): It regulates the levels of gene expression by involving specific mRNAs and either promoting their degradation or inhibiting the translation.

• Small interfering RNA (siRNA): Also like miRNA, it is involved in the RNAi process to suppress the genes' expression or rather their functions.

• Small nuclear RNA (snRNA): A protein that is linked to RNA splicing, to ensure the right pre-mRNA is transformed before the RNA is translated into protein.

RNA Synthesis (Transcription)

The transcription process is discussed below:

Transcription is the process in which there is synthesis of RNA molecule from a DNA molecule by using the DNA as a template. In eukaryotic organisms, occurs in the nucleolus while in prokaryotic organisms, occurs in the cytoplasm. The most vital ingredient of transcription is RNA polymerase.

Enzymes Involved

RNA polymerase is the enzyme, which synthesizes RNA with the help of a DNA matrix. It attaches itself to the DNA at certain sites known as promoters and then it opens up the furrows of the DNA to reveal the template strand.

Steps In Transcription

Following are the steps of the transcription:

Initiation

• In this case, RNA polymerase will initially bind to the promoter site with the DNA strand.

• The regulator sequence stretches to welcome the gene it promotes, and determines which of the two DNA bases has the function of an RNA base.

Elongation

• In RNA polymerase it works as in DNA polymerase it synthesises RNA in the 5’ to 3’ direction.

• It pays out the one in front of it and takes up the one behind repairing each rung by incorporating nucleotides that are in turn complementary to the DNA template strand also known as the antisense strand.

• The RNA strand grows as long as the RNA polymerase is within the process of translocation in the DNA molecule.

Termination

• Transcription continues until the RNA polymerase gets to the end signal or terminal point of the gene or DNA sequence to be transcribed.

• In prokaryotes, termination may be caused by the form/shape of DNA in the RNA which hails the process to an abrupt stop.

Diagram Of The Transcription Process

RNA Processing

In eukaryotic cells, RNA undergoes essential processing steps to form mature mRNA:

Capping

Capping: A 7methylguanosine cap attached to the 5’ end of pre-mRNA benefits it by shielding it and lending a hand for translation to begin.

Splicing

Excision of introns and linking of exons is carried out by spliceosomes which are made of snRNPs and proteins.

Polyadenylation

Polyadenylation of the mRNA at the 3’ end also stabilises the mRNA, helps it to export out of the nucleus and also promotes translation.

Role Of Spliceosomes

Spliceosomes are involved in the identification of splice sites in a molecule to facilitate accurate incision of the introns and accurate coalition of the exons to give rise to multiple mRNAs from a single gene through a process called alternative splicing.

RNA Translation (Protein Synthesis)

It is the process by which information in mRNA is translated into a sequence of amino acids that make up a protein. It takes place in the cytoplasm of prokaryotic as well as eukaryotic cells.

The role of :

• Ribosomes: It should be noted that ribosomes are the organelles where the translation process takes place. They are made up of two subunits that assemble around the mRNA during translation; large, and small.

• mRNA: Messenger RNA is responsible for the transportation of the genetic code from DNA to the location known as the ribosome. It holds codons which are three nucleotide triplets that will deliver a distinct thought of amino acids.

• tRNA: Hold annotate Some transfer RNA molecules bring amino acids to the ribosome. Each tRNA has a three-base sequence called anticodon and it pairs with the mRNA codon to bring the correct amino acid to the chain that is growing progressively.

Steps In Translation

Following are the steps in the process of translation:

Initiation

• The small ribosomal subunit with the help of initiation factors attaches to the mRNA at the start codon which is AUG.

• The first tRNA which is the initiator tRNA acquires methionine (N-formyl methionine in prokaryotes) and bonds with the start codon.

• Forms a functional ribosome by joining of large ribosomal subunit.

Elongation

• Translations also occur in the 5’ to 3 ‘ direction on the mRNA while the ribosome keeps on travelling for the process.

• When each mRNA codon of the protein is translated in the process on the A site of the ribosome, corresponding tRNA molecules bring in amino acids.

• Protein synthesis involving the process of peptide bond formation involves; adjacent amino acids linked with the help of a ribosome.

• The ribosome shifts so that the next codon of the mRNA is positioned over a new A site of the ribosome and other tRNAs arrive in the complex.

Termination

• Translation proceeds until the RBS is followed by a stop codon – UAA, UAG or UGA).

• Release factors bind to the ribosome and lead to what and then the polypeptide chain is released from the tRNA in the P site.

• The ribosomes say they are done translating the amino acid sequence and pull apart; the newly formed protein emerges.

Diagram Of The Translation Process

RNA Viruses

RNA viruses are classified as those viruses, which contain RNA as the genome of that particular virus. It ranges from Influenza viruses, Coronaviruses, Hepatitis C viruses, and Human Immunodeficiency viruses (HIV). These types of viruses can in turn be further classified as positive sense RNA viruses, negative sense RNA viruses and double-stranded RNA viruses all of which have different processes of replication and structure.

Replication Mechanisms Of RNA Viruses

• Positive sense RNA viruses: These viruses integrate their RNA genome to directly message RNA. When the virus infects the host cell, viral proteins are produced immunologically from the RNA without the DNA phase. The RNA also serves as a template during RNA replication through the action of viral RNA polymerase to produce more viral genera.

• Negativesense RNA viruses: These viruses have RNA genomes which refer to mRNA. Once within the cell, the viral RNA polymerase synthesises a positive sense RNA, a message RNA to synthesise viral proteins and a template to synthesize more viral RNA strands.

• Double-stranded RNA viruses: These viruses contain RNA as their genetic material and they have the positive sense RNA strands together which also has the negative sense RNA strands. Before it gets enclosed in a cell it is in a double-stranded form of RNA and part of it is used for replication to form more ecological forms of the virus by the viral RNA polymerase while the other part is used to translate viral proteins.

Impact On Human Health

Are RNA viruses pathogenic in humans they include; minor illnesses like colds which are caused by rhinoviruses to severe illnesses like COVID-19 caused by the coronavirus. In principle, they can quickly penetrate through populations because of a high mutation rate that results in the appearance of new viral serotypes possessing the ability to overcome the immune response or antiviral therapy. RNA viruses are problematic since they bring spurts and sometimes pandemics, therefore surveillance, vaccination, and antiviral research should be encouraged.