The key difference between aminoacyl tRNA and peptidyl tRNA is that aminoacyl tRNA is a tRNA molecule bound to the A site of the ribosome while peptidyl tRNA is a tRNA molecule bound to the P site of the ribosome.
Transfer RNA (tRNA) is an RNA molecule that helps to decode a messenger RNA (mRNA) sequence into a protein. In protein synthesis, the tRNA molecule makes base pairs with its complementary sequence on the mRNA (messenger RNA). This ensures that the appropriate amino acid is inserted into the growing polypeptide chain (protein molecule). Therefore, tRNA is an essential component for the translation step of protein synthesis. Aminoacyl tRNA and peptidyl tRNA are two types of tRNA molecules that participate in the translation step of the protein synthesis.
CONTENTS
1. Overview and Key Difference
2. What is Aminoacyl tRNA
3. What is Peptidyl tRNA
4. Similarities – Aminoacyl tRNA and Peptidyl tRNA
5. Aminoacyl tRNA vs Peptidyl tRNA in Tabular Form
6. Summary – Aminoacyl tRNA vs Peptidyl tRNA
What is Aminoacyl tRNA?
Aminoacyl tRNA is a tRNA molecule that bears a single amino acid at the terminus. It usually binds to the adjacent A site of the ribosome. The aminoacyl tRNA, along with particular elongation factors, delivers the specific amino acid to the ribosome for incorporation into the polypeptide chain during translation. Every amino acid has its own specific aminoacyl tRNA synthetase enzyme. This enzyme is utilized by amino acids to chemically bound to the specific tRNA. The binding of a tRNA with its cognate amino acid is crucial. This ensures that only the specific amino acid that matches the anticodon of tRNA is used during protein synthesis. In order to prevent translational errors, the aminoacyl tRNA synthetase enzyme has proofreading ability. The amino acids that are misacylated with the proper tRNA molecule usually undergo hydrolysis. This is carried out by the deacylation mechanism of the aminoacyl tRNA synthetase enzyme. Furthermore, the mischarged tRNA should be hydrolyzed in order to prevent incorrect protein synthesis.
Figure 01: Aminoacyl tRNA
In addition to the function in protein synthesis, aminoacyl tRNA also may function as a donor of amino acids necessary for the modification of lipids and the biosynthesis of antibiotics. Moreover, it is also understood that gene clusters may utilize aminoacyl tRNA to regulate the synthesis of encoded polypeptides.
What is Peptidyl tRNA?
Peptidyl tRNA is a tRNA molecule that is bound to the P site of the ribosome. After the initiation complex has formed properly, the translation proceeds by elongation of the polypeptide. The ribosome has three sites for tRNA binding: P (peptidyl), A (aminoacyl) and E (exist).
Figure 02: Peptidyl tRNA
The initiator methionyl tRNA is always bound to the P site. The next aminoacyl tRNA binds to the A site with the help of an elongation factor (EF-Tu in prokaryotes and eEf-1α in eukaryotes) and GTP. After binding, the GDP (hydrolyzed GTP) molecule is released. Later, a peptide bond is formed between methionyl tRNA at the P site and the second aminoacyl tRNA at the A site. This reaction is catalyzed by the peptidyl transferase enzyme. This reaction transfers methionine to the aminoacyl tRNA at the A site, thus forming a peptidyl tRNA. Moreover, during the translocation stage, peptidyl tRNA moves to the P site of the ribosome with the help of elongation factors (EFG in prokaryotes and eEf-2 in eukaryotes) and GTP hydrolysis. In addition, the uncharged tRNA first moves to the E site of the ribosome then leaves the E site at the end of the process.
What are the Similarities Between Aminoacyl tRNA and Peptidyl tRNA?
- Aminoacyl tRNA and peptidyl tRNA are two types of tRNA molecules that participate in translation.
- Both are tRNA molecules made up of ribonucleotide bases: adenine, cytosine, guanine, and uracil.
- Amino acids are associated with both molecules.
- They play vital roles in protein synthesis.
- Both participate in the elongation step of the translation.
What is the Difference Between Aminoacyl tRNA and Peptidyl tRNA?
Aminoacyl tRNA is a tRNA molecule that is bound to the A site of the ribosome, while peptidyl tRNA is a tRNA molecule that is bound to the P site of the ribosome. So, this is the key difference between aminoacyl tRNA and peptidyl tRNA. Furthermore, aminoacyl tRNA bears a single amino acid at the terminus while peptidyl tRNA bears a peptide chain at the terminus.
The below infographic lists the differences between aminoacyl tRNA and peptidyl tRNA in tabular form for side by side comparison.
Summary – Aminoacyl tRNA vs Peptidyl tRNA
tRNA is a molecule that helps to decode an mRNA sequence into a protein. Aminoacyl tRNA and peptidyl tRNA are two types of tRNA molecules that participate in the translation process. Aminoacyl tRNA is bound to the A site of the ribosome during the translation process, while peptidyl tRNA is bound to the P site of the ribosome during the translation process. Thus, this summarizes the difference between aminoacyl tRNA and peptidyl tRNA.
Reference:
1. “Aminoacyl-TRNA.” An Overview | ScienceDirect Topics.
2. “Peptidyl-TRNA.” An Overview | ScienceDirect Topics.
Image Courtesy:
1. “Charge tRNA” By Boumphreyfr – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “Elongation thumb” By User07 (CC BY-SA 3.0) via Commons Wikimedia