Question

RECALL Does mRNA bind to one or to both ribosomal subunits in the course of protein synthesis?

Short answer

mRNA binds to both ribosomal subunits during protein synthesis.

Step-by-step solution

- Understand the Role of mRNA

mRNA, or messenger RNA, carries the genetic information from DNA to the ribosome, where it serves as a template for protein synthesis.

- Recognize Ribosomal Subunits

Ribosomes consist of two subunits: a small subunit and a large subunit. These subunits work together to translate mRNA into a protein sequence.

- Determine the Binding of mRNA

During the initiation phase of protein synthesis, mRNA binds to the small ribosomal subunit first. Once the start codon is recognized and the first tRNA is in place, the large ribosomal subunit joins to form the complete ribosome. This means that mRNA initially binds to the small subunit and later to the assembled ribosome which consists of both subunits.

- Conclusion

mRNA interacts with both the small and large ribosomal subunits during the course of protein synthesis. It starts with the small subunit and then the large subunit joins during the synthesis process.

Key concepts

messenger RNA (mRNA)

Messenger RNA (mRNA) plays a crucial role in the process of protein synthesis. It carries the genetic instructions from the DNA, located in the cell's nucleus, to the ribosome, which is the site of protein synthesis in the cytoplasm. These instructions are essentially a sequence of nucleotides, which encode the blueprints for building proteins.

To achieve this, mRNA undergoes a transcription process.

• First, an enzyme called RNA polymerase reads the DNA sequence and synthesizes a complementary strand of mRNA.
• This mRNA then exits the nucleus and heads to a ribosome in the cytoplasm.

Once at the ribosome, the mRNA serves as a template for translating the nucleotide sequence into a chain of amino acids, which will eventually fold into a functional protein.

ribosomal subunits

Ribosomes are the molecular machines responsible for protein synthesis, consisting of two distinct subunits: a small subunit and a large subunit. Each subunit is composed of ribosomal RNA (rRNA) and proteins.

The small ribosomal subunit is responsible for reading the mRNA strand. It essentially sets the stage for translation by accurately positioning the mRNA.
The large ribosomal subunit is responsible for forming the peptide bonds between amino acids, ultimately building the protein chain. Together, these subunits form a complete ribosome.

During the initiation of protein synthesis, these subunits work in tandem.

• Initially, the small subunit binds to the mRNA strand.
• Once the start codon (AUG) is recognized and the first transfer RNA (tRNA) is in place, the large subunit joins the assembly.

This results in a functional ribosome capable of synthesizing proteins as it moves along the mRNA strand.

initiation of protein synthesis

The initiation of protein synthesis is a critical step where all the necessary components come together to start translating mRNA into a protein. This process involves multiple steps:

1. The mRNA binds to the small ribosomal subunit. This is facilitated by specific sequences on the mRNA that help it align correctly.

2. A tRNA molecule, carrying the amino acid methionine, pairs with the start codon (AUG) on the mRNA. This tRNA is known as the initiator tRNA.

3. After the initiator tRNA is in place, the large ribosomal subunit joins the complex. This forms a complete ribosome, ready for the elongation phase of protein synthesis.

During this initiation phase:

• The small ribosomal subunit ensures the correct placement of mRNA and tRNA.
• The large ribosomal subunit joins later to facilitate the formation of peptide bonds between amino acids, beginning the process of building a new protein.

The correct assembly and functioning of these components are what kick-start the translation process, leading to successful protein synthesis.