Question

RECALL Describe the role of stop codons in the termination of protein synthesis.

Short answer

Stop codons signal the end of protein synthesis by causing the ribosome to release the new protein and dissociate.

Step-by-step solution

Define Stop Codons

Stop codons are specific sequences in the mRNA that signal the termination of protein synthesis. These codons are UAA, UAG, and UGA.

Understand the Role in Translation

During translation, the ribosome reads the mRNA sequence to synthesize a protein. When a stop codon is reached, it does not code for any amino acid.

Interaction with Release Factors

When the ribosome encounters a stop codon, release factors (proteins) bind to the ribosome. This triggers the release of the newly synthesized protein from the ribosome.

Disassembly of the Translation Complex

After the protein is released, the ribosome subunits dissociate from the mRNA and each other, concluding the translation process.

Key concepts

termination of protein synthesis

Termination of protein synthesis is an essential step in the overall process of translating mRNA into a functional protein. This step ensures that the protein chain ends at the right position and is released properly.

The process starts when the ribosome encounters a stop codon on the mRNA strand. Stop codons are special signals within the genetic code that indicate the end of the protein-coding sequence. There are three primary stop codons: UAA, UAG, and UGA.

When the ribosome reaches any of these stop codons, it does not recognize them as regular codons that code for amino acids. Instead, it recognizes them as signals to stop the elongation of the protein chain. This crucial step ensures proteins are made correctly and completely.

translation process

The translation process is the biological machinery that converts the genetic information encoded in mRNA into a specific sequence of amino acids, ultimately forming a protein.

This process occurs in a few key steps:

• **Initiation**: The ribosome assembles around the target mRNA, and the first tRNA is attached at the start codon.
• **Elongation**: The ribosome travels along the mRNA, reading codons and adding corresponding amino acids to build the polypeptide chain.
• **Termination**: When a stop codon is reached, the translation process is halted, and the protein is released.

The ribosome plays a pivotal role throughout the translation process, moving along the mRNA and facilitating the binding of tRNAs and their corresponding amino acids.

Understanding these steps is crucial as they are the foundation of how genetic information is expressed and utilized in cells.

release factors

Release factors are special proteins that facilitate the termination of protein synthesis. When the ribosome encounters a stop codon during translation, these factors bind to the ribosome.

The key release factors in eukaryotes are eRF1 and eRF3. In bacteria, the main release factors are RF1, RF2, and RF3.

The role of release factors includes:

• **Recognizing Stop Codons**: They identify and bind to stop codons on the mRNA.
• **Promoting Hydrolysis**: They help hydrolyze the bond between the polypeptide chain and the tRNA in the P site of the ribosome.
• **Facilitating Disassembly**: They trigger the release of the newly synthesized protein and the disassembly of the ribosome complex from the mRNA.

This action is crucial because it ensures that translation halts at the correct point, preventing the synthesis of incomplete or defective proteins.

ribosome

The ribosome is a complex molecular machine that drives the translation process. It is composed of two subunits: the large subunit and the small subunit.

In both eukaryotic and prokaryotic cells, ribosomes have a similar structure and function, although their sizes and specific components can slightly differ.

Key functions of the ribosome include:

• **mRNA Binding**: It provides a site for mRNA to bind and be read.
• **tRNA Binding**: It facilitates the binding of tRNA molecules that carry amino acids to the growing polypeptide chain.
• **Catalyzing Peptide Bonds**: It catalyzes the formation of peptide bonds between adjacent amino acids, ensuring the protein chain elongates properly.

The importance of the ribosome cannot be overstated. It is the site where genetic codes are translated into functional proteins, playing a vital role in all cellular activities.

Understanding its structure and function helps unravel the complexities of how cells operate and maintain life processes.