mRNA – Messenger RNA: Encodes amino acid sequence of a polypeptide.
tRNA – Transfer RNA: Brings amino acids to ribosomes during translation.
rRNA – Ribosomal RNA: With ribosomal proteins, makes up the ribosomes, the organelles that translate the mRNA.

In both prokaryotes and eukaryotes, there are three main types of RNA – messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). These 3 types of RNA are discussed below.

Messenger RNA (mRNA)

mRNA accounts for just 5% of the total RNA in the cell. mRNA is the most heterogeneous of the 3 types of RNA in terms of both base sequence and size. It carries complimentary genetic code copied, from DNA during transcription, in the form of triplets of nucleotides called codons.

Each codon specifies a particular amino acid, though one amino acid may be coded for by many different codons. Although there are 64 possible codons or triplet bases in the genetic code, only 20 of them represent amino acids. There are also 3 stop codons, which indicate that ribosomes should cease protein generation by translation.

As part of post-transcriptional processing in eukaryotes, the 5’ end of mRNA is capped with a guanosine triphosphate nucleotide, which helps in mRNA recognition during translation or protein synthesis. Similarly, the 3’ end of an mRNA has a poly-A tail or multiple adenylate residues added to it, which prevents enzymatic degradation of mRNA. Both the 5’ and 3’ end of an mRNA imparts stability to the mRNA.

Transfer RNA (tRNA)

Transfer ribonucleic acid (tRNA) is a type of RNA molecule that helps decode a messenger RNA (mRNA) sequence into a protein. tRNAs function at specific sites in the ribosome during translation, which is a process that synthesizes a protein from an mRNA molecule. Proteins are built from smaller units called amino acids, which are specified by three-nucleotide mRNA sequences called codons. Each codon represents a particular amino acid, and each codon is recognized by a specific tRNA. The tRNA molecule has a distinctive folded structure with three hairpin loops that form the shape of a three-leafed clover. One of these hairpin loops contains a sequence called the anticodon, which can recognize and decode an mRNA codon. Each tRNA has its corresponding amino acid attached to its end. When a tRNA recognizes and binds to its corresponding codon in the ribosome, the tRNA transfers the appropriate amino acid to the end of the growing amino acid chain. Then the tRNAs and ribosome continue to decode the mRNA molecule until the entire sequence is translated into a protein.

Ribosomal RNA (rRNA)

Ribosomal RNA molecule in cells that forms part of the protein-synthesizing organelle known as a ribosome and that is exported to the cytoplasm to help translate the information in messenger RNA (mRNA) into protein. The three major types of RNA that occur in cells include rRNA, mRNA, and transfer RNA (tRNA).

Structure of the 30S subunit from T. thermophilus (left) and structure of the 50S subunit from D. radiodurans. From Ribosomal structure, and ribosome-antibiotic interactions.

Reference: https://serc.carleton.edu/microbelife/research_methods/genomics/ribosome.html

Ribosomes are the universal ribonucleoprotein particles that translate the genetic code into proteins. They are built of two subunits that associate upon initiation of protein synthesis. Typical eubacterial ribosomes (70S) consist of 57 different molecules (3 rRNAs and 54 proteins) and can dissociate into a small (30S) and a large subunit (50S). The small subunit is responsible for the formation of the initiation complex, performs the decoding of the genetic information, and controls the fidelity of codon-anticodon interactions. The large subunit catalyzes the peptide bond formation and provides the path for the nascent polypeptide chain.

Ribosomal RNA

Reference: https://www.youtube.com/watch?v=_W2YpBbZZ9w

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