Functional RNAs are RNA molecules that are not translated into proteins but perform various essential roles within the cell. They can be categorized based on their function. Here are some of the major types of functional RNA:
Types of Functional RNA
The classification of functional RNAs can be approached based on their cellular role. Below is a table and list summarizing the key types.
| Type | Abbr. | Function |
|---|---|---|
| Messenger RNA | mRNA | Carries genetic code from DNA to ribosomes for protein synthesis |
| Ribosomal RNA | rRNA | Forms the core of ribosomes, the protein synthesis machinery |
| Transfer RNA | tRNA | Transports amino acids to the ribosome for protein synthesis |
| Signal Recognition Particle RNA | 7SL RNA / SRP RNA | Directs ribosomes to the endoplasmic reticulum for protein targeting |
| Small Nuclear RNA | snRNA | Involved in splicing of pre-mRNA |
| MicroRNA | miRNA | Regulates gene expression by binding to mRNA and inhibiting translation |
| Long Non-coding RNA | lncRNA | Diverse regulatory roles in gene expression, chromatin modification, etc. |
| Piwi-interacting RNA | piRNA | Protects genome integrity by silencing transposons |
| Circular RNA | circRNA | Can act as miRNA sponges, regulate transcription, and potentially translate proteins |
Here's a breakdown of each type with more detail:
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Messenger RNA (mRNA): Serves as the template for protein synthesis. It carries the genetic code from DNA to the ribosomes, where proteins are assembled.
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Ribosomal RNA (rRNA): A major component of ribosomes, providing the structural and enzymatic framework for protein synthesis. rRNA ensures correct codon-anticodon interaction during translation.
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Transfer RNA (tRNA): Adapts the genetic code by carrying specific amino acids to the ribosome. Each tRNA molecule recognizes a specific codon on the mRNA and delivers the corresponding amino acid to the growing polypeptide chain.
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Signal Recognition Particle RNA (7SL RNA or SRP RNA): Facilitates the translocation of proteins across the endoplasmic reticulum membrane. SRP RNA is part of the signal recognition particle complex which binds to signal peptides of nascent proteins and guides them to the ER.
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Small Nuclear RNA (snRNA): Plays a crucial role in RNA splicing, a process that removes introns (non-coding regions) from pre-mRNA to form mature mRNA. snRNAs are components of spliceosomes, the molecular machines that catalyze splicing.
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MicroRNA (miRNA): Regulates gene expression post-transcriptionally. miRNAs bind to complementary sequences on mRNA molecules, leading to mRNA degradation or translational repression.
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Long Non-coding RNA (lncRNA): A diverse class of RNA molecules longer than 200 nucleotides that do not code for proteins. lncRNAs have various regulatory functions, including chromatin remodeling, transcription regulation, and splicing modulation.
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Piwi-interacting RNA (piRNA): Primarily found in germ cells and protects the genome by silencing transposons (mobile genetic elements). piRNAs bind to PIWI proteins, forming complexes that target and suppress transposon activity.
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Circular RNA (circRNA): Forms a covalently closed loop. They can function as miRNA sponges (binding and sequestering miRNAs), regulate transcription, and in some cases, be translated into proteins.
These different types of functional RNA demonstrate the versatility and importance of RNA beyond its role as a simple intermediate in protein synthesis. They participate in a wide range of cellular processes, highlighting the complex regulatory networks within living organisms.
