Discuss the structure and functionofribosomes and their roleinprotein synthesis The energy that drives the formation of a peptide bond in the ribosome is not directly supplied by an external source during the catalytic step itself, but rather is stored within the activated amino acid attached to its transfer RNA (tRNA). This stored energy, often referred to as a high-energy bond, is released when the aminoacyl-tRNA in the A-site of the ribosome undergoes a nucleophilic attack on the ester carbon of the peptidyl-tRNA in the P-site. This fundamental process of peptide bond formation is central to protein synthesis, where ribosomes act as the molecular machinery to link amino acids together in a specific sequence.
Contrary to what might be initially assumed, the ribosome itself does not generate the energy for peptide bond formation. Instead, this energy is meticulously prepared during the "charging" of the tRNA molecules. This charging process, catalyzed by aminoacyl-tRNA synthetases, involves the activation of an amino acid and its covalent attachment to a specific tRNA molecule. This attachment forms a high-energy ester bond between the amino acid and the 3' end of the tRNA. It is the breaking of this high-energy ester bond during the peptidyl transferase reaction within the ribosome that provides the necessary thermodynamic driving force for the formation of the peptide bond.
While the energy is pre-stored in the aminoacyl-tRNA, the ribosome plays a crucial role in facilitating and accelerating this reaction. The ribosome's active site, primarily composed of ribosomal RNA (rRNA) within the large subunit, acts as a peptidyl transferase center. It efficiently positions the substrates—the aminoacyl-tRNA and the peptidyl-tRNA—in close proximity and in the correct orientation for the reaction to occur.The term "charging" is appropriate, since thehigh-energy bond that attaches an amino acid to its tRNAis later used to drive the formation of the peptide bond. This precise positioning, along with potential catalytic contributions from the rRNA and surrounding ribosomal proteins, significantly speeds up peptide bond formation, making it orders of magnitude faster than it would be in a non-enzymatic setting. Some research also suggests that the ribosome employs entropic catalysis, which involves reorganizing water molecules and positioning substrates optimally within the active site to lower the activation energy.
The formation of a peptide bond itself, from the perspective of the amine and carboxylate components, can be considered an exothermic reaction under cellular conditions when coupled with the hydrolysis of the high-energy bond in the aminoacyl-tRNA.作者：TW Giessen·2012·被引用次数：84—One of those enzyme classes capable of catalyzingpeptide bond formationis the acyl-AMP ligase family that activates a substrate carboxylate as an adenylate for subsequent nucleophilic attack, similar to the activation reaction found in NRPS-systems, and additionally catalyzes the subsequentformation... This means that energy is released during the process, which is essential for driving the reaction forward and ensuring efficient protein elongation2022年12月24日—The energy for each peptide bond formation is derived from thehigh-energy bondlinking each amino acid to its tRNA.. The energy utilized is essentially a form of chemical energy conversion, where energy stored in the aminoacyl-tRNA bond is transferred to the newly formed peptide bond.
It is important to distinguish the energy source for peptide bond formation from the energy expenditure required for the initial activation of amino acids.16 Quantum Transition State for Peptide Bond Formation in ... The charging of tRNA molecules by aminoacyl-tRNA synthetases typically requires energy input, often in the form of ATP (adenosine triphosphate). For instance, the formation of aminoacyl-AMP, an intermediate in the charging process, consumes one ATP molecule. Subsequently, the amino acid is transferred to the tRNA, releasing AMP. While ATP is indirectly involved in preparing the charged tRNA, it is the high-energy ester bond linking the amino acid to the tRNA that directly drives the peptide bond formation within the ribosome. Therefore, while cells invest energy through processes like ATP hydrolysis to charge tRNAs, no *additional* input of energy from sources like ATP is directly needed at the moment of peptide bond formation within the ribosome's catalytic site.
In summary, the energy that drives formation of peptide bond in ribosome originates from the high-energy bond that attaches an amino acid to its tRNAPeptide Bond Formation Mechanism Catalyzed by Ribosome. This energy is released during the catalytic process orchestrated by the ribosome, which acts as a highly efficient peptidyl transferase.Ribosomes | Biology for Majors I While ATP is consumed during the initial charging of tRNA, the peptide bond formation step itself relies on the energy stored within the activated aminoacyl-tRNA, making it a coupled, thermodynamically favorable reaction that powers the continuous elongation of polypeptide chains during protein synthesis.2025年8月6日—Kinetic experiments have determined that theenergybarrier ofribosome-catalyzedpeptide formationis 14.00 kcal·mol −1 , 13.60 kcal·mol ...
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