large ribosomal subunit

Definition

Target type: cellularcomponent

The larger of the two subunits of a ribosome. Two sites on the ribosomal large subunit are involved in translation, namely the aminoacyl site (A site) and peptidyl site (P site). [ISBN:0198506732]

The large ribosomal subunit (LSU) is a complex molecular machine responsible for catalyzing peptide bond formation during protein synthesis. It consists of ribosomal RNA (rRNA) and ribosomal proteins (r-proteins) that assemble into a highly structured, three-dimensional entity. The LSU is significantly larger and more complex than the small ribosomal subunit (SSU), containing three major rRNA molecules (28S, 5.8S, and 5S rRNA in eukaryotes) and around 49 different proteins in eukaryotes.

The LSU's primary function is to bind the messenger RNA (mRNA) and transfer RNA (tRNA) molecules involved in protein synthesis. It also houses the peptidyl transferase center (PTC), a critical catalytic site where peptide bonds are formed between amino acids.

Here is a detailed description of the major components of the LSU:

**1. rRNA:** The LSU contains three rRNA molecules: 28S, 5.8S, and 5S rRNA. These molecules are highly structured and provide the structural framework for the subunit. The 28S rRNA is the largest and most abundant, forming the core of the LSU. It contains multiple domains with specific functions, including the peptidyl transferase center (PTC), which is crucial for peptide bond formation. The 5.8S rRNA is located in close proximity to the 28S rRNA and interacts with it to maintain the overall structure. The 5S rRNA interacts with proteins and participates in stabilizing the LSU structure.

**2. r-proteins:** The LSU contains approximately 49 proteins in eukaryotes, each with a unique role in the subunit's structure and function. These proteins bind to the rRNA molecules, stabilizing the overall structure, and facilitating the binding of tRNA and mRNA molecules. Some of these proteins are involved in the assembly of the LSU, while others participate in the catalytic activity of the subunit.

**3. Peptidyl Transferase Center (PTC):** The PTC is a highly conserved catalytic site located within the 28S rRNA molecule. It is responsible for catalyzing peptide bond formation between amino acids. The PTC is a complex region that involves specific nucleotides from the 28S rRNA and interactions with proteins.

**4. tRNA binding sites:** The LSU contains three binding sites for tRNA molecules: the A site, the P site, and the E site. The A site accepts the incoming aminoacyl-tRNA, the P site holds the tRNA molecule carrying the growing polypeptide chain, and the E site is where the deacylated tRNA leaves the ribosome. These binding sites are crucial for the accurate positioning of tRNA molecules during protein synthesis.

**5. mRNA binding site:** The LSU interacts with the mRNA molecule via the SSU, ensuring the correct positioning of the mRNA for translation.

The LSU is a complex and highly dynamic structure that plays a crucial role in protein synthesis. Its intricate components, including rRNA molecules, proteins, and catalytic sites, work together to ensure the accurate and efficient translation of genetic information into functional proteins.
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Proteins (11)

Compounds (23)