The mRNA has a linear structure that has a uracil base instead of a thymineand its secondary structure could be a hairpin, a stem-loop, etc.; whereas the tRNA has a structure from sheet which carries three specific stem loops; and the rRNA has a much more complex with numerous folds and loops.
The mRNA acts as messenger of the DNAtRNA transports amino acids during protein synthesis; rRNA is the producer of proteins of the cell. All three of these RNAs play a vital role in the process of transcription and also in protein synthesis. These are essential factors for every cell, as life would not be possible in their absence.
Ribonucleic acid is abbreviated as RNA, which is the active compound in cellular protein synthesis. It has a high molecular weight and acts as genetic code in some virus. They have nitrogenous bases such as adenine, guanine, cytosine and uracil (replacing thymine in DNA). They are single-stranded biopolymers. RNA has ribose nucleotides where the nitrogenous bases are attached to the ribose sugar which are linked by phosphodiester bonds forming the chain or strands of different lengths.
In 1965, RW Holley described the structure of RNA. The essential and significant process in molecular biology is the flow of information genetics in a cell, which consists of three steps; DNA produces RNA that leads to proteins. Proteins are therefore considered the workhorses of the cell, performing essential functions in the cell.
So, every time the cell needs some protein, it sends signals activating the genes for that particular protein and the DNA that encodes that protein, produces multiple copies of that part which are then processed, transcribed and translated.
The process of RNA transcription is mediated by the RNA polymerase (enzyme) that builds the RNA complement to template DNA. The method of transcription is properly controlled by three main factors, promoter, regulator and inhibitor.
In this context, we will discuss the structural and functional differences between the three types of RNA in cells. eukaryotes.
Comparison chart mRNA tRNA and rRNA
| BASIS FOR COMPARISON | mRNA | tRNA | rRNA |
|---|---|---|---|
| Sense | The mRNA, or messenger RNA, is the connection between the gene and protein, and is the result of the gene transcribed by RNA polymerase. | The tRNA or transfer RNA is a molecule RNA molecule and provides specific amino acids to ribosomes. | The rRNA or Ribosomal RNA is used for the formation of ribosomes. |
| Paper | The mRNA transports genetic information from the nucleus to ribosomes for protein synthesis. | tRNA transports specific amino acids to ribosomes to aid in protein biosynthesis. | rRNAs provide the structural framework for ribosome formation. |
| Synthesised in | Core. | Cytoplasm. | Ribosome. |
| Size | In mammals, the size of molecules is around 400 to 12 000 nucleotides (nt). | The size of the tRNA molecule is 76 to 90 nucleotides (nt). | The size of the rRNA molecule can vary between 30S, 40S, 50S and 60S. |
| Shape | The mRNA is linear in shape. | tRNA is cloverleaf-shaped. | rRNA is sphere-shaped (complex structure). |
| Composed of | The mRNA is made up of codons. | tRNA is composed of anticodons. | rRNA does not have codon sequences or anticodon. |
Definition of mRNA
The synthesis of messenger RNA or mRNA takes place in the nucleus (in eukaryotes) as heterogeneous nuclear RNA (hnRNA). In addition, hnRNA processing releases mRNA. This (mRNA) will then enter the cytoplasm to participate in protein synthesis.
The mRNA has a short half-life, with a high molecular weight. These are said to be the link between the gene and the protein. This form of RNA or eukaryotic mRNA is exclusively modified (post-transcription modification) only to avoid hydrolysis by 5′-exonucleases (enzyme). Therefore, these are capped at the 5′-terminal ends by 7-methylguanosine triphosphate. This protection also aids in the recognition of mRNA for protein synthesis.
At the 3′-terminal end of the mRNA is a polymer of adenylate residues (20 to 20 nucleotides) known as poly(A) tails or polyadenosine tails. This tail provides mRNA stability and also prevents attack by 3′-exonucleases.
The mRNA molecules also have certain modified bases such as 6-methyladenylate in the internal structure; these mRNAs also have a intronwhich is spliced before the formation of the mature mRNA molecule.
Definition of tRNA
Transfer RNA or tRNA is soluble RNA, the molecules contain approximately 75 nucleotides and have a molecular weight of 25,000. There are 20 tRNA species corresponding to 20 amino acids present in the protein structure. The structure of tRNA was first described by Holley.
During the translation of proteins, tRNA is the decoder of the mRNA message. The structure of tRNA resembles the cloverleaf model. The structure has four arms: the acceptor arm, the anticodon arm, the D arm, the TψC arm and the variable arm.
The acceptor arm is capped with the CCA sequence (5′ to 3′). Amino acids bind to the acceptor arm. The acceptor arm has three specific nucleotide bases (anticodons), which recognise the triplet codon of the mRNA. While the D arm is named after the presence of dihydrouridine. The TψC arm has the sequence of T, pseudouridine and C. The variable arm is the most variable arm and has two categories which are Class I and Class II tRNAs.
The tRNA is also modified after transcription such as inosine, methylguanosine and pseudouridine. This is done to include non-standard bases. As the ribosome cannot form proteins with the help of mRNA; the anticodon, a sequence of three key tRNA bases is complementary to the codon of three mRNA bases.
This is the first major function of tRNA, and then the process continues as each molecule carries an amino acid that matches the mRNA codon.
Definition of rRNA
Ribosomal RNA or rRNA is the main factor in ribosomes. These are factories for protein synthesis. Eukaryotic ribosomes consist of two nucleoprotein complexes: the 60S and 40S subunits. The 60s subunit is further divided into 28S RNA, 5S RNA and 5.8S RNA, while 40S RNA has 18S RNA as a subunit.
The function of rRNAs is unclear in ribosomes; it is thought that RNA molecules travel to the cytoplasm and bind with mRNA and other rRNA molecules and proteins to form ribosomes.
Key differences between mRNA, tRNA and rRNA
The following are critical points for understanding the variations between mRNA, tRNA and rRNA:
- The mRNA or messenger RNA is the link between the gene and the protein, which is formed from the gene transcribed by RNA polymerase; tRNA or transfer RNA is a cloverleaf-shaped RNA molecule and helps provide specific amino acids to ribosomes; rRNA or ribosomal RNA is used for the formation of ribosomes.
- mRNA transports genetic information from the nucleus to ribosomes for protein synthesis, while tRNA transports specific amino acids to ribosomes to aid in protein biosynthesis, and rRNA provides the structural framework for ribosome formation.
- The mRNA is synthesised in the nucleus, tRNA is synthesised in the cytoplasm, while rRNA is synthesised in the ribosome.
- In mammals, the size of the molecules mRNA molecule size is around 400 to 12 000 nucleotides (nt), while the size of a tRNA molecule is 76 to 90 nucleotides (nt) and that of rRNA can vary from 30S, 40S, 50S and 60S.
- mRNAs are shaped like linearThe tRNA has cloverleaf shape and the rRNA has sphere-shaped (complex structure).
- The mRNA is consists of codons, while tRNA is composed of anticodons, and rRNA has no codon or anticodon sequences.
Conclusion mRNA tRNA and rRNA
There are three main types of RNA in a cell, which are mRNA, tRNA, and rRNA. mRNAs are the message carriers and therefore initiate protein formation. This process also involves tRNA and rRNA, where tRNA brings the specific amino acids and rRNA plays a role in ribosome formation. The whole process takes place from the nucleus to the ribosome.