Difference Between mRNA tRNA and rRNA

Main Difference – mRNA tRNA vs rRNA

mRNA, tRNA, and rRNA are three major types of RNA found in the cell. Typically, RNA is a single-stranded molecule, composing of adenine, guanine, cytosine, and uracil in its structure. The pentose sugar is the ribose in all RNA nucleotides. RNA is produced by transcription, with the aid of RNA polymerase enzyme. Though each RNA type highly vary in their function, all three RNA types are mainly involved in protein synthesis. The main difference among mRNA tRNA and rRNA is that mRNA carries the coding instructions of an amino acid sequence of a protein while tRNA carries specific amino acids to the ribosome to form the polypeptide chain, and rRNA is associated with proteins to form ribosomes.

Key Areas Covered

1. What is mRNA
      – Definition, Features, Function
2. What is tRNA
      – Definition, Features, Function
3. What is rRNA
      – Definition, Features, Function
4. What are the Similarities Between mRNA tRNA and rRNA
      – Outline of Common Features
5. What is the Difference Between mRNA tRNA and rRNA
      – Comparison of Key Differences

Key Terms: Alternative Processing, Messenger RNA (mRNA), Ribosomal RNA (rRNA), Ribosomes, Proteins, Transcription, Translation, Transfer RNA (tRNA)

What is mRNA

Messenger RNA (mRNA) molecules carry a transcript of a gene, which encodes for a particular functional protein, from the nucleus to the ribosomes. The production of mRNA occurs by a process called transcription. The enzyme involved in the transcription is RNA polymerase. In eukaryotes, pre-mRNA molecules are processed to form mature RNA molecules through post-transcriptional modifications. The pre-mRNA processing includes 5′ cap addition, editing, and polyadenylation. A 7-methylguanosine cap is added to the front of the 5′ end. Some changes are allowed to the mRNA sequence by editing the sequence. A poly(A) tail with around 250 adenosine residues is added at the 3′ end of the mRNA molecule to protect it from degradation by exonucleases. On the other hand, eukaryotic pre-mRNA is composed of both introns and exons. Alternative splicing is another process by which different combinations of exons are spliced together to achieve several types of proteins from a single pre-mRNA molecule. Prokaryotic mRNA is capable of producing a single type of protein after translation.

Figure 1: Pre-mRNA processing

The mature mRNA molecules are exported through nuclear pore to the cytoplasm. The mature mRNA is translated into an amino acid sequence of a particular protein in a process called translation. Translation is facilitated by ribosomes in the cytoplasm. The transcription of a DNA sequence into an mRNA molecule and the translation of an mRNA molecule into a protein are called the central dogma of molecular biology. The coding region of each mRNA molecule is composed of codons, which are three nucleotides, representing a particular amino acid of the polypeptide chain. The formation of mature RNA from pre-mRNA is shown in figure 1.

What is tRNA

Transfer RNA (tRNA) is a type of a major RNA that specifically brings amino acids to the ribosomes during translation. Each codon in the mRNA molecule is read by the anticodon of the tRNA to bring the specific amino acid to the ribosome. Typically, a tRNA molecule is composed of about 76 to 90 RNA nucleotides. The secondary structure of tRNA is a clover-leaf shape. It is composed of four loop structures known as D-loop, anticodon loop, variable loop, and T-loop. Anticodon loop is composed of a specific anticodon that scans the complement codon in the mRNA molecule.

Figure 2: Transfer RNA

A tRNA molecule is also composed of an acceptor stem, which consists of a 5’ terminal phosphate group. The amino acid is loaded into the CCA tail at the end of the acceptor stem. Some anticodons form base pairs with several codons by the wobble base pairing. The secondary structure of a tRNA molecule is shown in figure 2.

What is rRNA

Ribosomal RNA (rRNA) is a type of major RNA that is involved in the formation of ribosomes along with ribosomal proteins. The ribosome is the protein-synthesizing organelle in the cell, translating the coding sequence on an mRNA molecule into a polypeptide chain. The synthesis of rRNA occurs at the nucleolus. Two types of rRNA molecules are synthesized as small rRNA and large rRNA. Both rRNA molecules combine with ribosomal proteins to form a small subunit and a large subunit. The large subunit of rRNA serves as the ribozyme that catalyzes the peptide bond formation. During translation, small subunit and large subunit come together to form the ribosome. The mRNA molecule is sandwiched between the small and large subunit. Each ribosome is composed of three binding sites for the binding of tRNA molecules. They are A, P, and E sites. The A site binds with the aminoacyl-tRNA. The aminoacyl-tRNA contains a specific amino acid. The aminoacyl-tRNA molecule at the P site is attached to the growing polypeptide chain. Then, the aminoacyl-tRNA molecule moves to the E site.

Difference Between mRNA tRNA and rRNA_Figure 3

Figure 3: Protein synthesis

Prokaryotes consist of 70S ribosomes, which are composed of 30S small subunit and 50S large subunit. Eukaryotes consist of 80S ribosomes, which are composed of 40S small subunit and 60S large subunit. Protein synthesis is shown in figure 3.

Similarities Between mRNA tRNA and rRNA

Each mRNA, tRNA, and rRNA are encoded by the genes in the nucleus.
The mRNA, tRNA, and rRNA are composed of adenine, guanine, cytosine, and uracil.
Both mRNA and rRNA are single-stranded molecules.
Both rRNA and tRNA do not work with DNA.

Definition

mRNA: An mRNA is a subtype of RNA molecule which carries a portion of the DNA code to other parts of the cell for processing.

tRNA: A tRNA molecule is a small RNA molecule, which is clover-leaf shaped and transfers a specific amino acid in the cytoplasm to the ribosome.

rRNA: An rRNA molecule is a component of the ribosome and serves as the organelle of translation.

Shape

mRNA: The mRNA is linear in shape.

tRNA: The tRNA is a clover-leaf shaped molecule.

rRNA: The rRNA is a sphere shaped molecule.

Function

mRNA: The mRNA carries the message of transcript DNA codes of polypeptides from the nucleus to the ribosomes.

tRNA: The tRNA carries specific amino acids to the ribosome, aiding the translation.

rRNA: The rRNA is associated with specific proteins to form ribosomes.

Codon/Anticodon

mRNA: The mRNA consists of codons.

tRNA: The tRNA consists of anticodons.

rRNA: The rRNA lacks codon or anticodon sequences.

Size

mRNA: The size of the mRNA molecule is typically 400 to 12,000 nt in mammals.

tRNA: The size of the tRNA molecule is 76 to 90 nt.

rRNA: The size of the rRNA can be either 30S, 40S, 50S, and 60S.

Conclusion

mRNA, tRNA, and rRNA are the three major types of RNA in a cell. All three types of RNA comprise a unique function in protein synthesis. The mRNA carries the message of a particular protein from the nucleus to the ribosome. The tRNA molecules bring specific amino acids to ribosomes. The rRNA molecules are involved in the formation of ribosomes, the organelle, which facilitate the translation. This is the difference between mRNA tRNA and rRNA.

Reference:

1. “Messenger RNA (mRNA).” Encyclopædia Britannica. Encyclopædia Britannica, inc., n.d. Web. Available here. 23 July 2017.
2. “TRNA: Role, Function & Synthesis.” Study.com. N.p., n.d. Web. Available here. 23 July 2017.
3. “Ribosomal RNA (rRNA).” Encyclopædia Britannica. Encyclopædia Britannica, inc., n.d. Web. Available here. 23 July 2017.

Image Courtesy:

1. “Pre-mRNA” By Nastypatty – Own work (CC BY-SA 4.0) via Commons Wikimedia
2. “TRNA-Phe yeast en” By Yikrazuul – Own work (CC BY-SA 3.0) via Commons Wikimedia
3. “Protein synthesis” By Mayera at the English language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia