Translation Protein Synthesis

Introduction to Protein Translation

Protein synthesis is completed by the process of protein translation. When the DNA molecule has transcribed a transcription, the messenger RNA is translated for protein synthesis. In the process of translation, messenger RNA works together with the transfer RNA i.e. (tRNA) and ribosome for the process of protein synthesis. The whole process of transcription and translation is called gene expression. Protein synthesis can be defined as the process in which the molecules of amino acids are arranged as a single line into proteins by involving ribosomal RNA, transfer RNA, messenger RNA, and other enzymes.


Translation Process in Protein Synthesis

The translation is a process of protein synthesis for mRNA with the help of ribosomes. Translational unit of mRNA from 5’ to 3` includes start codon, region coded polypeptide, a stop codon, and untranslated regions (UTRs) at 5`end & 3`end both for more efficiency of the process.


The ribosome is the place where the whole machinery of translation is present. Each eukaryotic ribosome has two parts smaller 40S subunit and a larger 60S subunit. The smallest unit has a point for attachment of mRNA. Along with the largest subunit, it forms a P-site or peptidyl transfer (Donor site).


There are binding sites for initiation factors, elongation factors, translocation, etc.


Structure and Role of tRNA in Protein Synthesis 

The transfer RNA is a family of about 60 small sized ribonucleic acids that can recognize the codon of mRNA and exhibit a higher affinity for 21 activated amino acids which combines with them and carries them to the site of protein synthesis. tRNA molecules have been variously termed as soluble RNA or supernatant RNA or adapted RNA of the cell.


Structurally, tRNA looks like a cloverleaf or inverted L shaped molecule which on one end has an amino acid receptor end and on the other end has an anticodon loop. The bent in the chain of each tRNA molecule contains a definite sequence of three nitrogenous bases that constitute the anticodon. It recognizes the codon on mRNA. 


The function of tRNA is specific in protein synthesis as they pick up specific amino acids from the amino acid pool and carry over the mRNA strand.


Protein Synthesis Steps Involved

  • Initiation involves assembling ribosomes around mRNA and activating amino acid and delivering it to the transfer RNA.

  • Elongation is the process in which  the RNA strand gets longer by adding amino acids 

  • The termination process only involves releasing a polypeptide chain.

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Explanation of Steps of Translation

1.Initiation

  • Initiation in prokaryotes requires large and small ribosome subunits, the mRNA, initiating transfer RNA, and 3 initiation factors (IFs).

  • Amino acids are activated by binding with the enzyme called aminoacyl tRNA synthetase in presence of ATP forming an enzyme complex and P site.

Amino acid and ATP in the presence of aminoacyl transfer RNA synthetase 🡪  Pi + AA-AMP-Enzyme complex

  • Transfer of amino acid to tRNA -

AA-AMP-Enzyme complex + transfer RNA 🡪 Amino Acid- tRNA + AMP + Enzyme.

  • Two sites at ribosome are present that are called A-site and P-site where units of ribosome bind to the cap region of messenger RNA and comparatively smaller units bind to mRNA followed by binding of them with the larger subunits. It makes AUG lie on P-site and methionyl tRNA binds to P-site.


2.Elongation of the Polypeptide Chain

  • At the 2nd codon, other aminoacyl transfer RNA complexes that are charged initiate binding at A-site.

  • At P-site- peptide bond between the carboxyl molecule and the amino molecule is observed whereas at A-site bond between amino molecule and amino acid is formed through the enzyme named as a peptidyl transferase.

  • Sliding of ribosome over messenger RNA from one codon to its alternate codon in the direction of 5’ to 3`.

  • A polypeptide chain is formed by the attachment of amino acids to one alternate to another in a chain formed by the peptide bond, and the attachment is based in accordance with the sequence of codons resulting in elongation of the protein chain.


3. Termination of Polypeptide

  • Reaching the A-site of the ribosome at a termination codon which is present, not coding for any amino acid, no charged transfer RNA binds to the A-site of ribosome.

  • A polypeptide is now not associated with the ribosome and dissociates and is catalyzed by a “release factor”, a factor that releases 3 termination codons called UGA, UAG, and UAA.


Protein Synthesis Diagram

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FAQ (Frequently Asked Questions)

1.Explain Which RNA is Involved in Protein Synthesis?

The process of translation takes place in the cytoplasm of the cell. Nucleus undergoes some modifications before it gets translated. Removal of unneeded sections and modification is done to protect the ends of the mRNA molecule and our mRNA molecule is ready for translation protein synthesis. Another RNA involved is called transfer RNA is in the shape of a cloverleaf with 3 loops. It has an anticodon site that has a special section in the middle of the loop and it also contains an amino acid site at its one end. Anticodon plays an important role to recognize a specific messenger RNA called start codon.

2. What Happens After the Process of Translation?

Transcription and Translation are the two processes entirely called the gene expression which results in the production of a polypeptide chain and when a polypeptide chain is synthesized, further it undergoes few additional processes.


For example, It might acquire a folded shape due to the interactions between the amino acids of the chain. It can also get attached to the other polypeptides or some different types of structures such as lipids or carbohydrates. Many of the proteins reach the Golgi apparatus in the cytoplasm which is to be modified to perform a few specific functions of the nucleus.