Q.(a) What is meant by translation in protein synthesis ?
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Start your 14-day free trial to unlock the full solution →Translation is the process of synthesizing proteins from mRNA, and tRNA charging, or aminoacylation, is the essential step where specific amino acids are attached to their corresponding tRNA molecules, ensuring accuracy and providing energy for protein synthesis.
Gene expression, the process by which information from a gene is used in the synthesis of a functional gene product, primarily protein, is fundamental to all life. This complex process involves two major steps: transcription, where genetic information from DNA is copied into messenger RNA (mRNA), and translation, where this mRNA sequence is then used to synthesize proteins. The regulation of gene expression ensures that the right proteins are made at the right time and in the right amounts, allowing cells to adapt to their environment and perform specialized functions.
(a) What is meant by translation in protein synthesis?
Translation is the biological process by which the genetic information encoded in messenger RNA (mRNA) is decoded to synthesize a specific protein. Essentially, it is the conversion of the language of nucleic acids (a sequence of nucleotides) into the language of proteins (a sequence of amino acids). This process occurs in the cytoplasm of the cell, specifically on ribosomes, which act as the cellular machinery for protein synthesis.
The mRNA molecule carries the genetic code in the form of codons, which are sequences of three nucleotides. Each codon specifies a particular amino acid. During translation, these codons are read sequentially, and the corresponding amino acids are brought to the ribosome by transfer RNA (tRNA) molecules. The amino acids are then linked together in a specific order to form a polypeptide chain, which subsequently folds into a functional protein. The entire process proceeds in a directional manner, from the 5' end to the 3' end of the mRNA, resulting in a polypeptide synthesized from its N-terminus to its C-terminus.
The central dogma of molecular biology describes this flow of genetic information: DNA makes RNA (transcription), and RNA makes protein (translation).
(b) Explain charging of tRNA (aminoacylation of tRNA) and mention its importance in the process of translation.
Charging of tRNA (Aminoacylation of tRNA)
Before translation can begin, the transfer RNA (tRNA) molecules, which act as adapter molecules, must be "charged" or "aminoacylated." This means that each tRNA molecule must be covalently linked to its specific amino acid. This crucial process ensures that the correct amino acid is delivered to the ribosome according to the mRNA codon.
The charging of tRNA is catalyzed by a highly specific enzyme called aminoacyl-tRNA synthetase. There is at least one specific aminoacyl-tRNA synthetase for each of the 20 standard amino acids. This enzyme recognizes both a specific amino acid and its corresponding tRNA molecule.
The process occurs in two main steps:
- Activation of Amino Acid: The specific amino acid first reacts with ATP (adenosine triphosphate) in the presence of the aminoacyl-tRNA synthetase. This reaction forms an aminoacyl-AMP complex and releases pyrophosphate (PPi). This step activates the amino acid, making it ready for attachment to tRNA.
- Transfer to tRNA: The activated aminoacyl-AMP complex then transfers the amino acid to the 3'-hydroxyl group of the terminal adenosine nucleotide at the 3' end of its cognate tRNA molecule. AMP is released in this step. The resulting molecule is called an aminoacyl-tRNA, or a charged tRNA.
The specificity of aminoacyl-tRNA synthetase is paramount. It ensures that the correct amino acid is attached to the correct tRNA, which is vital for the accuracy of protein synthesis. If the wrong amino acid is attached, it will be incorporated into the growing polypeptide chain, leading to a potentially non-functional protein.
Importance of Charging of tRNA in Translation …
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