Question

What role does peptidyl transferase play in protein synthesis? (A) It transports the initiator aminoacyl-tRNA complex. (B) It helps the ribosome to advance three nucleotides along the mRNA in the \(5^{\prime}\) to \(3^{\prime}\) direction. (C) It holds the protein in its tertiary structure. (D) It catalyzes the formation of a peptide bond.

Short answer

Option (D): It catalyzes the formation of a peptide bond.

Step-by-step solution

Understanding Peptidyl Transferase

Peptidyl transferase is an enzymatic component of the ribosomal RNA that plays a crucial role in the process of translation during protein synthesis.

Analyzing the Function

Peptidyl transferase specifically catalyzes the formation of peptide bonds, which link amino acids together to form a polypeptide chain.

Matching to the Correct Option

From the given options, we need to find the one that corresponds to the function of catalyzing the formation of a peptide bond.

Eliminate Incorrect Options

Option (A) involves transporting the initiator aminoacyl-tRNA complex, which is not a function of peptidyl transferase. Option (B) involves the ribosome moving along the mRNA, which is facilitated by elongation factors. Option (C) involves holding the protein in its tertiary structure, a function performed by chaperone proteins.

Selecting the Correct Answer

Option (D) states that peptidyl transferase catalyzes the formation of a peptide bond, which directly aligns with its role in protein synthesis.

Key concepts

Catalysis of Peptide Bond

Peptidyl transferase is an essential enzyme-like component that plays a pivotal role in protein synthesis. During the translation process, its main function is to catalyze the formation of peptide bonds.
These peptide bonds are crucial because they link individual amino acids together, forming a long chain known as a polypeptide.
A polypeptide eventually folds into a functional protein.

• Peptide bonds form between the carboxyl group of one amino acid and the amino group of another.
• This bond-formation process releases water in a reaction known as dehydration synthesis.
• Peptidyl transferase ensures that the growing polypeptide chain remains attached to the ribosome, allowing protein synthesis to proceed smoothly.

The catalysis of peptide bonds by peptidyl transferase is a cornerstone of creating the primary structure of proteins, which is foundational for all life processes.

Ribosomal RNA Enzyme

Peptidyl transferase is a part of the ribosomal RNA (rRNA), making it a ribozyme, an RNA molecule capable of acting as an enzyme.
This capacity highlights the unique role of RNA not just as a messenger (mRNA) but also as a catalyst.

• Unlike traditional enzymes that are proteins, peptidyl transferase is built from RNA components.
• This enzymatic activity of rRNA emphasizes the central role of RNA in early biological evolution and intricate cellular processes.
• Being part of the rRNA within the large ribosomal subunit, it facilitates the peptide bond formation in the ribosome's active site.

Therefore, rRNA's enzymatic function highlights its versatility and essential role in the translation process, bridging the gap between genetic information and functional proteins.

Translation Process

The translation process is a fundamental mechanism in which the genetic information encoded in mRNA is converted into a functional protein. This complex process involves several key steps:

• Initiation: The small ribosomal subunit binds to the mRNA strand at the start codon (AUG).
• Elongation: tRNAs bring specific amino acids to the ribosome based on the codon sequence of the mRNA matching with their anticodon on tRNA. Peptidyl transferase here catalyzes peptide bonds between sequentially added amino acids.
• Termination: Once a stop codon is reached (UAA, UAG, or UGA), the newly formed polypeptide chain is released.

During elongation, peptidyl transferase plays a critical role.
By forming peptide bonds, it ensures the nascent polypeptide chain lengthens accurately with the correct amino acid sequence. Without this precise function, protein synthesis could not occur efficiently.