Question

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

Short answer

Stop codons signal the end of protein synthesis by binding release factors that facilitate polypeptide release, and disassemble the translation complex.

Step-by-step solution

Introduction to Stop Codons

Understand that stop codons are specific sequences of nucleotides in messenger RNA (mRNA) that signal the end of protein synthesis. There are three stop codons: UAA, UAG, and UGA.

Role in Termination

During translation, the ribosome reads the mRNA sequence to synthesize a polypeptide chain. When a stop codon is encountered in the A site of the ribosome, protein synthesis is terminated.

Mechanism of Termination

When a stop codon is reached, release factors bind to the stop codon in the ribosome. These proteins facilitate the release of the newly synthesized polypeptide from the ribosome.

Disassembly of the Translation Complex

After the polypeptide is released, the ribosome subunits dissociate along with the mRNA, making the components available for another round of translation.

Key concepts

protein synthesis termination

Protein synthesis is an essential biological process where cells build proteins. During this process, cells use the genetic code from mRNA to create specific proteins. However, this synthesis doesn't go on forever. It needs to stop at some point, which is where stop codons come into play. Stop codons are specific sequences in mRNA such as UAA, UAG, and UGA that signal the end of protein synthesis. When the ribosome encounters a stop codon, it knows that the polypeptide chain is complete and should be released.

mRNA sequence

Messenger RNA (mRNA) is a type of RNA that carries genetic information from DNA to the ribosome. The ribosome reads the mRNA sequence in sets of three nucleotides, called codons. Each codon specifies a particular amino acid or a stop signal during protein synthesis. In this series, stop codons such as UAA, UAG, and UGA play a crucial role. They signal to the ribosome that translation is complete. Without these stop signals, the process would continue indefinitely, leading to nonfunctional proteins.

ribosome function

The ribosome is the molecular machine that translates the mRNA sequence into a polypeptide chain. This complex has two subunits that work together to read the mRNA and synthesize proteins. As the ribosome moves along the mRNA strand, it reads each codon and adds the corresponding amino acid to the growing polypeptide chain. When the ribosome encounters a stop codon in the A site, it recognizes that the translation process should end. Release factors then help with the termination process, ensuring the polypeptide is correctly released and the ribosome components are ready for another round of translation.

release factors

Release factors are proteins that play a crucial role in the termination of protein synthesis. When the ribosome encounters a stop codon, release factors bind to this codon within the ribosome. Their role is to facilitate the release of the newly synthesized polypeptide chain from the ribosome. These factors ensure that the process halts efficiently, preventing any unwanted continuation of the polypeptide chain. After the polypeptide is released, release factors also help in disassembling the translation complex, allowing the ribosome and mRNA to separate and be reused for future rounds of protein synthesis.