Question

Describe the role of the stop signals in protein synthesis.

Short answer

Stop signals, or stop codons, indicate the end of translation, ensuring the release of the completed polypeptide chain.

Step-by-step solution

Understand the Process of Protein Synthesis

Protein synthesis is the process by which cells build proteins. This process occurs in two main stages: transcription and translation.

Comprehend Transcription

During transcription, the DNA sequence of a gene is copied into mRNA. This mRNA then carries genetic information from the DNA in the nucleus to the ribosomes in the cytoplasm.

Learn About Translation

Translation occurs in the ribosome where the mRNA is decoded to produce a specific polypeptide. tRNA molecules bring amino acids to the ribosome in the correct order, matching their anticodon with codons on the mRNA.

Define Stop Codons

Stop codons are specific sequences of nucleotides in the mRNA (UAA, UAG, and UGA) that signal the end of translation. They do not code for amino acids, but instead tell the ribosome to stop synthesis.

Role of Stop Signals in Termination

When a ribosome encounters a stop codon, it recognizes that the protein synthesis process is complete. Release factors (proteins that help in the termination process) bind to the stop codon, prompting the ribosome to release the newly formed polypeptide chain.

Summary of the Role of Stop Signals

Stop signals (stop codons) are crucial for indicating when a protein has been fully synthesized. They ensure the polypeptide chain is released correctly so it can fold into a functional protein.

Key concepts

Protein Synthesis

Protein synthesis is a vital biological process that cells use to generate proteins. This intricate process occurs in two major stages: transcription and translation.
During these stages, the genetic information encoded in DNA is translated into functional proteins. Proteins are essential for numerous cellular functions, including structure, enzymes, and signal transduction. Understanding the full picture of protein synthesis helps in appreciating how genetic information is expressed and utilized in living organisms.

Transcription

Transcription is the first step of protein synthesis, where the DNA sequence of a gene is transcribed into messenger RNA (mRNA). This stage occurs in the nucleus of eukaryotic cells.
Enzymes known as RNA polymerases facilitate the process by unwinding the DNA and synthesizing a complementary strand of RNA. The resulting mRNA is a temporary copy of the gene, carrying the genetic information needed for protein synthesis.
Once formed, the mRNA exits the nucleus and travels to the ribosomes in the cytoplasm, where the next stage of protein synthesis takes place.

Translation

Translation is the process through which the mRNA sequence is decoded to produce a specific polypeptide, which later folds into a functional protein. This stage occurs in the ribosome, a complex molecular machine found in the cytoplasm.
Transfer RNA (tRNA) molecules play a crucial role in this process. Each tRNA molecule has an anticodon that matches a specific codon on the mRNA strand, ensuring that amino acids are added in the correct order.
The ribosome reads the sequence of codons on the mRNA, and tRNA molecules bring the appropriate amino acids, linking them together to form a polypeptide chain. This chain will eventually fold into a protein with a specific function.

Stop Codons

Stop codons are specific nucleotide sequences in the mRNA that signal the end of the translation process. There are three stop codons in the genetic code: UAA, UAG, and UGA.
Unlike regular codons that code for amino acids, stop codons act as a termination signal for protein synthesis. When the ribosome encounters a stop codon during translation, it recognizes that the protein is complete and should be released.
The importance of stop codons lies in their role in ensuring that proteins are synthesized accurately, and that the polypeptide chain is not extended unnecessarily.

Termination of Translation

The termination of translation is the final stage of protein synthesis, marked by the ribosome encountering a stop codon on the mRNA. When this happens, release factors, which are specialized proteins, bind to the stop codon.
These release factors prompt the ribosome to release the newly synthesized polypeptide chain. After release, the polypeptide folds into its functional three-dimensional shape. Proper termination is crucial for the functionality of the resulting protein.
This last step ensures that the protein synthesis process is concluded correctly, allowing the ribosome to be reused for the synthesis of more proteins.