RNA : Structure, Functions and Types

RNA (ribonucleic acid) is a type of nucleic acid that is essential for many biological functions, including the control of genetic information, protein synthesis, and gene expression.

Although there are a few significant distinctions, RNA and DNA (Deoxyribonucleic acid) have structural similarities.

The following sentence summarises the structure of it-


It is made up of nucleotides, which are the RNA molecules’ building blocks.
Each nucleotide consists of three components:

1. Pentose Sugar

It contains ribose sugar, which is a five-carbon sugar molecule.

2. Phosphate Group

A phosphate group is attached to the ribose sugar, providing a negatively charged group.

Nitrogenous Base

Adenine (A), guanine (G), cytosine (C), and uracil (U) are the four distinct nitrogenous bases found in it
Uracil replaces thymine found in DNA.

Single-Stranded Structure

Unlike DNA, which typically forms a double helix structure, It is generally single-stranded. However, some RNA molecules can fold back on themselves, forming complex secondary structures.

Base Pairing

The nitrogenous bases in RNA can form specific base pairs. Adenine (A) forms two hydrogen bonds with uracil (U), and guanine (G) forms three hydrogen bonds with cytosine (C). This base pairing allows RNA to fold and form various secondary structures.

1. Primary Structure

The linear arrangement of nucleotides in the RNA molecule is referred to as its fundamental primary structure. The sequence of nucleotides determines the genetic information encoded in the it.

2. Secondary Structure

It’s molecules can adopt various secondary structures through base pairing interactions.

This folding is driven by complementary base pairing between different regions of the same RNA molecule.

Common secondary structures include hairpins, loops, stems, and bulges.

3. Tertiary Structure

In addition to secondary structure, some RNA molecules can form more complex tertiary structures.

Tertiary structure involves interactions between distant parts of the RNA molecule, resulting in a three-dimensional arrangement .Many RNA molecules, including ribosomes and ribozymes, depend on their tertiary structure to operate correctly.

Types of RNA

There are mainly types of Ribonucleic acid are present in cell. they play important roles in various cellular processes. The major types of it include:

1. Messenger RNA (mRNA)

It is Single-stranded. mRNA carries genetic information from DNA to the ribosomes in the cytoplasm. mRNA serves as a template for protein synthesis during the process of translation.
It does not have a double helix structure and can fold into complex secondary structures due to complementary base pairing within the molecule.
The discovery of mRNA is attributed to scientists François Jacob and Jacques Monod in the 1960s, who elucidated its role in carrying genetic information from DNA to the ribosomes during protein synthesis.

Function of mRNA

  • Carries genetic information from DNA to ribosomes.
  • Transcribed from DNA template during transcription.
  • Contains codons that specify amino acids for protein synthesis.
  • Interacts with ribosomes for translation and protein synthesis.
  • Involved in gene regulation and controlling gene expression.

2. Transfer RNA (tRNA)

It is responsible for carrying amino acids to the ribosomes during protein synthesis. Each tRNA molecule recognizes a specific codon on the mRNA and brings the corresponding amino acid to the growing polypeptide chain.

tRNA: The presence of tRNA and its role in transporting amino acids to the ribosomes was first described by scientists Robert W. Holley, Har Gobind Khorana, and Marshall W. Nirenberg in the 1960s.

tRNA has a characteristic cloverleaf-like secondary structure. It consists of several stem-loop structures formed by base pairing within the molecule.

tRNA has four arms.

1. Acceptor Arm (3′ CCA Arm)

Location: This arm is located at the 3′ end of tRNA.
Structure: The CCA sequence is made up of the three nucleotides cytosine (C), cytosine (C), and adenine (A).

Function: The CCA sequence serves as the attachment site for the specific amino acid that corresponds to the tRNA molecule.

2. D Arm (Dihydrouridine Arm)

Location: The D arm is located opposite the anticodon arm.
Structure: It contains a variable number of base pairs and usually contains the modified nucleotide dihydrouridine (D) within the stem-loop structure.

Function: The D arm helps stabilize the overall structure of tRNA and is involved in interactions with the ribosome during translation.

3. Anticodon Arm

Location: The anticodon arm is located opposite the D arm.
Structure: It contains the anticodon, which is a specific sequence of three nucleotides that recognizes and binds to the complementary codon on mRNA during translation. The anticodon loop is usually in a stem-loop structure.

Function: The anticodon arm enables tRNA to recognize and pair with the appropriate codons on mRNA, ensuring the accurate translation of the genetic code.

4. TΨC Arm (Thymine-Pseudouridine-Cytosine Arm):

Location: The TΨC arm is located adjacent to the anticodon arm.
Structure: It contains the sequence TΨC (thymine-pseudouridine-cytosine), where pseudouridine is a modified form of uridine.
Function: The TΨC arm contributes to the stability and proper folding of tRNA. It also interacts with specific enzymes involved in tRNA modification and processing.

3. Ribosomal RNA (rRNA)

The cellular organelle known as ribosomes, which are reponsible of protein synthesis, contain rRNA as one of their constituents. It provides structural support and catalytic functions during the translation process.

The role of rRNA in protein synthesis was discovered by scientists George E. Palade, Albert Claude, and Christian de Duve in the 1950s, leading to their shared Nobel Prize in Physiology or Medicine in 1974.
Structure of rRNA:

It found in ribosomes. It is single-stranded ribonucleotides.

rRNA molecules have a complex three-dimensional structure, with numerous stem-loop regions formed by intramolecular base pairing.

Function of rRNA

Ribosome Structure: rRNA plays a vital role in the structural framework of ribosomes. The two ribosome subunits, referred to as the large and small subunits, are made when rRNA combines with riboproteins.

  1. Catalytic Activity: Certain regions of rRNA possess catalytic activity, enabling them to carry out crucial steps in protein synthesis.
  2. Ribosome Assembly: rRNA molecules are involved in the assembly of ribosomes by providing a scaffold for the binding of ribosomal proteins.
  3. Translation: During translation, rRNA acts as the site for mRNA binding and provides the platform for the assembly of tRNA molecules carrying amino acids. It facilitates the accurate alignment of mRNA codons with the anticodons of tRNA, allowing the synthesis of proteins based on the genetic information carried by mRNA.
  4. Peptide Bond Formation: rRNA contains the peptidyl transferase center, which catalyzes the formation of peptide bonds between amino acids, leading to the elongation of the polypeptide chain during protein synthesis.
  5. Ribosome Stability and Function: rRNA contributes to the stability, integrity, and overall function of ribosomes. It ensures the proper alignment of mRNA and tRNA molecules, allowing the ribosome to decode the genetic information and synthesize proteins accurately.

Different Terms Related to RNA

Here are some important terms to related to ribonucleic acids-

1. Vault-associated small RNA III (vsRNA III)

vsRNA III is a small non-coding RNA molecule that associates with vault particles. It has been implicated in the regulation of stress responses and cellular homeostasis.

2. Small Temporal RNA-Like (stRNA-like)

stRNA-like molecules are small non-coding RNA molecules that share similarities with stRNA. They are involved in the regulation of gene expression and developmental processes.

3. Circular RNA-derived from intron (circIntron)

circIntrons are circular RNA molecules that are derived from intronic regions of genes. They are generated through back-splicing events during RNA processing and may play roles in gene regulation and cellular functions.

4. Small Polyadenylated Nuclear RNA (snoRNA)

snoRNAs are a class of small non-coding RNA molecules that primarily localize to the nucleolus. They guide the chemical modification of ribosomal RNA (rRNA) and other RNA molecules, contributing to their functional maturation.

5. Small H/ACA RNA (snoRNA-H/ACA)

snoRNA-H/ACA molecules are a subtype of snoRNA that guide the pseudouridylation of target RNA molecules. Pseudouridylation is a post-transcriptional modification that influences RNA structure and function.


The CRISPR-Cas system, a bacterial immune mechanism that defends against viral and plasmid DNA, has RISPR RNA as one of its components.
crRNA guides the Cas proteins to target and degrade complementary invading DNA.

7. Small Nuclear RNA (snRNA)

The pre-mRNA splicing process, which involves cutting off introns (non-coding areas) and combining exons (coding regions) to create mature mRNA, depends critically on small nuclear RNA.

8. Small Nucleolar RNA (snoRNA)

Small Nucleolar RNA is involved in the modification of other RNA molecules, particularly ribosomal RNA. It guides the chemical modifications and processing of rRNA molecules.

9. MicroRNA (miRNA)

Post-transcriptional gene regulation involves microRNA.It binds to complementary sequences on mRNA molecules and prevents their translation into proteins or leads to their degradation.

10. Long Non-Coding RNA (lncRNA)

A large class of RNA molecules known as long non-coding RNA regulate gene expression, chromatin remodelling, and other cellular functions even though they do not code for proteins.

11. Piwi-Interacting RNA (piRNA)

Piwi-Interacting RNA is mainly involved in silencing transposable elements (repetitive DNA sequences) in germ cells. It helps in maintaining genome stability and regulating gene expression during germline development.

12. Small Interfering RNA (siRNA)

An RNA molecule known as small interfering RNA participates in the RNA interference (RNAi) pathway. It plays a role in gene regulation by binding to complementary mRNA sequences and triggering their degradation or inhibiting their translation.

13. Small Nucleolar RNA-Derived RNA (sdRNA)

sdRNA is derived from small nucleolar RNA (snoRNA) and is involved in regulating gene expression and RNA processing.

14. Telomerase RNA (TERC)

The telomerase enzyme complex, which includes telomeraseRNA, aids in preserving the length of telomeres, the protective caps on the ends of chromosomes. It is involved in cellular aging and the replication of DNA.

15. Vault RNA (vtRNA)

It is a component of vault particles, which are large ribonucleoprotein complexes found in the cytoplasm. Although the significance of vtRNA in cellular transport and potential defence mechanisms is not fully known, it is believed to be important.

16. Y RNA

A short non-coding RNA molecule called Y-RNA is involved in a number of biological functions, such as stress reactions, RNA processing, and DNA replication. It forms complexes with specific proteins and contributes to their functionality.

17. Circular RNA (circRNA)

CircRNA is a type of RNA molecule that forms a closed loop structure, unlike the linear structure of most RNA molecules. CircRNAs have been linked to a number of biological functions and disorders, and it has been discovered that they regulate the expression of genes.

18. Enhancer RNA (eRNA)

It is transcribed from DNA sequences called enhancers. It has been implicated in the regulation of gene expression by facilitating the activation of specific genes and influencing chromatin structure.

19. Antisense RNA

A RNA molecule known as antisenseRNA is complementary to a certain mRNA sequence. It can bind to the target mRNA and regulate gene expression by mechanisms such as mRNA degradation or inhibition of translation.

20. Vault-associated Small RNA (vasRNA)

vasRNA is a class of small non-coding RNAs that associate with vault particles. These RNAs have been observed to be involved in diverse cellular processes, including development, immune responses, and cancer.

21. Long Intergenic Non-Coding RNA (lincRNA)

Long non-coding RNA molecules, known as lincRNAs, are actively transcribed from intergenic regions between genes in the genome. They play a crucial role in diverse biological processes, including chromatin remodeling, gene regulation, and development.

22. Vault-associated small temporal RNA (vtRNA)

vtRNA, also known as small-temporalRNA (stRNA), is a small non-coding RNA molecule that associates with vault particles. It is involved in the regulation of cellular processes such as cell division and cell growth.

23. Pseudogene RNA

It is transcribed from pseudogenes, which are DNA sequences similar to functional genes but do not produce functional proteins. Pseudogene RNA molecules can have regulatory functions and may play a role in gene expression regulation.

24. Circular Intronic RNA (ciRNA)

ciRNA is a type of circularRNA that is derived from introns, which are non-coding regions within genes. ciRNAs are involved in regulating gene expression by interacting with RNA polymerase II and promoting gene transcription.

25. Transcription start site-associated RNA (TSSa-RNA)

It is transcribed from the region near the transcription start site of genes. It has been suggested to play a role in the regulation of gene expression and the recruitment of transcription factors.

26. Promoter-associated RNA (paRNA)

It is transcribed from the promoter regions of genes and is involved in the regulation of gene expression. It can interact with chromatin remodeling factors and transcriptional regulators to influence gene activity.

27. Repeat-associated small interfering RNA (rasiRNA)

rasiRNAs are small RNA molecules that are involved in gene silencing mechanisms associated with repetitive DNA elements, such as transposons. They play a role in maintaining genome stability and regulating gene expression.

28. Long Stress-Induced Non-Coding Transcript (lncRNA)

lncRNAs are a diverse class of long non-coding RNA molecules. lncRNAs are a subset of lncRNAs that are specifically induced under stress conditions. They participate in stress response pathways and regulate gene expression to adapt cells to stressful environments.

29. Exosome RNA

Exosomes are small vesicles released by cells that contain various types of RNA. Exosome RNA includes different RNA species, such as mRNA, miRNA, and lncRNA. These RNAs can be transferred between cells and play roles in intercellular communication and modulation of cellular processes.

30. Vault RNA-like particle (vlRNA):

vlRNA is a non-coding RNA molecule that shares similarities with vtRNA but is structurally distinct. It is found in the cytoplasm and nucleus and may have functions in RNA processing and transport.

31. Circular RNA-derived from exons (circExons)

Circular RNA molecules, known as circExons, derive from exonic regions of genes through back-splicing events during RNA processing. Researchers have implicated them in various biological processes, including gene regulation and cellular differentiation.

32. Trans-acting small interfering RNA (ta-siRNA)

ta-siRNAs actively participate in gene silencing as small RNA molecules. They originate from long non-coding RNA precursors and play a role in regulating gene expression through RNA interference pathways.

33. Small Cajal body-specific RNA (scaRNA)

scaRNAs are small non-coding RNA molecules found in Cajal bodies, subnuclear structures involved in RNA processing and modification. scaRNAs guide chemical modifications, such as methylation and pseudouridylation, of other RNA molecules, including rRNA and snRNA.

34. Small Modulatory RNA (smRNA)

smRNAs are a class of small non-coding RNA molecules that have regulatory functions in gene expression. They include small regulatory RNAs such as small activating RNAs (saRNAs) and small inhibitory RNAs (siRNAs).

35. Trans-acting siRNA (tasiRNA)

tasiRNAs are a type of siRNA that are produced from non-coding RNA precursors called TAS genes. They play a role in gene regulation and development by targeting specific mRNAs for degradation or translational repression.

36. Long Intergenic RNA Activator (lincRNA-Activator)

lincRNA-Activators are long non-coding RNA molecules that have been identified as regulators of gene expression. They interact with protein complexes to activate the expression of target genes.

37. Vault-associated Small RNA II (vsRNA II)

sRNA II is a small non-coding RNA molecule that associates with vault particles. It has been found to have a regulatory role in stress response pathways and immune system functions.

38. Circular RNA-derived from exonic sequences with open reading frames (circORF)

circORFs are circular RNA molecules that originate from exonic sequences containing open reading frames (ORFs). Some circORFs have been found to encode functional peptides or proteins, adding a new layer of complexity to the understanding of circularRNAs.

39. Ribozymes

Ribozymes are RNA molecules that possess catalytic activity. They actively perform specific chemical reactions similar to the functions of enzymes and researchers have discovered them in various biological processes, including RNA processing and protein synthesis.

It possess catalytic activity, meaning they can accelerate specific chemical reactions. They are unique because, traditionally, enzymes were thought to be exclusively composed of proteins.

Ribozymes have implications in biotechnology, where they can be engineered for various applications, such as gene therapy and RNA-based diagnostics.

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