7 Types of RNA with Structure and Functions

RNA, also known as ribonucleic acid, is a nucleotide polymer composed of ribose sugar, phosphate, and bases such as adenine, guanine, cytosine, and uracil.

Different Types of RNA 

RNA polymerase produces RNA from DNA that is either protein-coding (messenger RNA, mRNA) or non-coding (RNA genes). Because of their functionalities, they are classified into following types of RNA:

mRNA (Messenger RNA)

It is a type of RNA that transports genetic information from DNA to the ribosome, where it acts as a template for protein production.

Structure: mRNA is a one-stranded chain of ribonucleotides (adenine, cytosine, guanine, and uracil) with a sugar-phosphate backbone. It includes both exons (coding sequences) and introns (non-coding sections). In eukaryotes, freshly produced RNA (pre-mRNA) is converted into functional mRNA by 5′ cap addition, 3′ poly-A tail addition, and splicing to link exons and eliminate introns within the nucleus.

Functions:

• mRNA acts as a messenger, carrying genetic instructions from DNA to ribosomes for protein synthesis.
•  It regulates gene expression by determining which genes are expressed and translated into proteins.
• The type and number of proteins produced are influenced by the amount of mRNA produced for a particular gene.

tRNA (Transfer RNA)

It is a type of RNA molecule that is essential in the process of converting the genetic information from mRNA into a sequence of amino acids that create a protein.

Structure: Transfer RNA (tRNA) has a cloverleaf structure with four arms: anticodon for mRNA pairing, D for folding, TΨC for ribosome binding, and a variable loop. The amino acid is attached to the acceptor stem at the 3′ end, which has a CCA sequence. In 3D, tRNA creates an L-shaped structure, placing the anticodon for mRNA binding and the amino acid opposite for protein synthesis, guaranteeing precise translation of genetic information.

Functions:

• tRNA anticodons couple with corresponding mRNA codons to ensure that the protein’s amino acids are in the right sequence.
• It transports particular amino acids to the ribosomes, ensuring that amino acids are properly incorporated into the developing protein chain.
• Plays an important part in peptide bond formation by arranging the amino acids in correct order on the ribosome, allowing for the production of a polypeptide chain.

rRNA (Ribosomal RNA)

They are types of RNA that forms up the basic structural and functional components of ribosomes, the molecular machinery that synthesize proteins in cells.

Structure: Ribosomal RNA (rRNA) is the fundamental structure of ribosomes, which is required for protein synthesis. Ribosomes in prokaryotes consist of a 30S subunit containing 16S rRNA and a 50S subunit containing 5S and 23S rRNA. Ribosomes in eukaryotes have two subunits: the 40S, which contains 18S rRNA, and the 60S, which contains 5S, 5.8S, and 28S rRNAs. These rRNAs aid in the ribosome’s assembly, structural stabilization, and peptide bond creation, allowing mRNA to be translated into proteins more efficiently.

Functions:

• It binds with proteins to form ribosomes, which are responsible for protein synthesis.
• It is essential for ribosomal enzymatic function, allowing amino acids to form peptide bonds during protein synthesis.
• It interacts with mRNA and tRNA to ensure that the genetic code is correctly read and translated during protein synthesis.

snRNA (Small Nuclear RNA)

They are types of RNA which is present in the nucleus of eukaryotic cells that form complexes with proteins to engage in pre-mRNA splicing, allowing the removal of introns and the joining of exons during mRNA processing.

Structure: Small nuclear RNA (snRNA) are tiny RNA molecules found in the nucleus of eukaryotic cells. They are generally 100-300 nucleotides long and have stem-loop structures that are critical for their function in RNA processing. They form complexes with proteins called small nuclear ribonucleoprotein particles (snRNPs), which play critical roles in pre-mRNA splicing by detecting splice junctions and catalyzing splicing events.

Functions:

• It aids in the removal of introns (non-coding areas) from pre-mRNA molecules and the assembly of exons (coding regions) to generate mature mRNA.
•  It joins with proteins to produce spliceosomes, which are huge molecular complexes that precisely splice pre-mRNA.
• It interacts with other proteins and RNA molecules to regulate gene activity, such as transcription and translation.

miRNA (Micro RNA)

They are a types of RNA (non-coding) that is vital for controlling gene expression.

Structure: MicroRNAs (miRNAs) are short, single-stranded RNA molecules, typically 20-25 nucleotides long, with a stem-loop structure. After processing by Dicer, the mature miRNA is incorporated into the RNA-induced silencing complex (RISC) to regulate gene expression by targeting messenger RNA (mRNA) molecules for degradation or translational repression.

Functions:

• It can attach to mRNA molecules and impede their translation into proteins, regulating gene expression levels.
• It affects cell differentiation, tissue morphogenesis, and organ creation.
• Dysregulation of miRNA expression has been linked to a variety of illnesses, including cancer, cardiovascular issues, and neurological conditions.

siRNA (Small Interfacing RNA)

They are types of RNA molecule that may mute particular genes by identifying and destroying their messenger RNA (mRNA) equivalents, hence controlling gene expression.

Structure: Small interfering RNA (siRNA) is a double-stranded RNA molecule that is around 20-25 nucleotides long and has a duplex structure with two unpaired nucleotides at the 3′ ends. One strand, called the guide strand, is integrated into the RNA-induced silencing complex (RISC), directing it to target messenger RNA (mRNA) for destruction or translational repression, effectively silencing gene expression.

Functions:

• It binds to complementary mRNA sequences and causes their destruction, blocking the expression of certain proteins encoded by those genes.
• It is a component of the RNA interference (RNAi) pathway, which protects cells against viral infections by targeting viral RNA for destruction.
• It may be utilized in research and medicine to selectively quiet disease-causing genes, potentially treating a variety of hereditary illnesses and viral infections.

lncRNA (Long Non-Coding RNA)

They are longer types of RNA molecule that does not encode proteins and instead performs numerous regulatory roles in gene expression and cellular activities.

Structure: Long non-coding RNAs (lncRNA) are RNA molecules longer than 200 nucleotides that do not encode proteins yet regulate a variety of biological functions. They may form complex structures and interact with proteins, DNA, and other RNA molecules to control gene expression on several levels.

Functions:

• It may interact with DNA, RNA, and proteins to regulate gene expression, either increasing or inhibiting it.
• It is involved in a variety of cellular activities, including as chromatin remodeling, epigenetic control, and alternative RNA splicing.
• Dysregulation of lncRNA expression has been linked to a variety of illnesses, including cancer, cardiovascular ailments, and neurological conditions.

To summarize, different types of RNA play important roles in cellular machinery and genetic information control. Messenger RNA (mRNA) acts as a template for protein synthesis, transporting genetic information from DNA to ribosomes. Ribosomal RNA (rRNA) and transfer RNA (tRNA) are essential components of translation, ensuring that amino acids are correctly assembled into proteins. Other non-coding types of RNA, such as microRNA (miRNA) and long non-coding RNA (lncRNA), regulate gene expression, maintain cellular homeostasis, and influence developmental processes. The complicated actions of these types of RNA molecules demonstrate their significance beyond being mere intermediates in gene expression, emphasizing their involvement in health, sickness, and evolution.

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