Termination

Definition

Termination is the final step in the processes of transcription and translation, marking the end of RNA synthesis and protein synthesis, respectively. In transcription, it occurs when RNA polymerase reaches a specific sequence on the DNA template, signaling it to stop synthesizing RNA. In translation, termination happens when the ribosome encounters a stop codon on the mRNA, leading to the release of the completed polypeptide chain. Both processes are crucial for gene expression and ensure that proteins are produced accurately.

5 Must Know Facts For Your Next Test

1. In prokaryotes, termination can occur through intrinsic or extrinsic mechanisms, involving specific sequences in the DNA that signal RNA polymerase to dissociate.
2. During translation termination, release factors bind to the ribosome upon encountering a stop codon, prompting the release of the newly synthesized polypeptide.
3. In eukaryotes, termination of transcription involves additional processing steps like polyadenylation, where a poly-A tail is added to the newly formed mRNA.
4. Both transcription and translation termination are tightly regulated processes to ensure proper gene expression and cellular function.
5. The accuracy of termination is vital because errors can lead to incomplete or malfunctioning proteins that could affect cellular activities.

Review Questions

• How do intrinsic and extrinsic mechanisms differ in prokaryotic transcription termination?
  • Intrinsic termination relies on specific sequences in the RNA that form a hairpin structure, causing RNA polymerase to detach from the DNA. Extrinsic termination involves additional proteins known as Rho factors that help release RNA polymerase from the DNA template. Both mechanisms ensure that transcription stops correctly to produce functional RNA.
• What role do release factors play during translation termination in protein synthesis?
  • Release factors are essential during translation termination as they bind to the ribosome when a stop codon is encountered on the mRNA. This binding triggers the hydrolysis of the bond between the polypeptide chain and the tRNA in the ribosome, leading to the release of the completed polypeptide. This step is critical for ensuring that proteins are released properly and can fold into their functional forms.
• Evaluate how errors in termination during transcription or translation could impact protein function and cellular processes.
  • Errors in termination can lead to incomplete or improperly synthesized proteins, which may not fold correctly or perform their intended functions. For instance, a truncated protein resulting from premature termination might lack essential domains necessary for its activity. Such dysfunctional proteins can disrupt cellular pathways, potentially leading to diseases or impaired cell function. Ensuring precise termination is thus crucial for maintaining cellular homeostasis and overall organism health.

Related terms

Stop Codon: A sequence of three nucleotides in mRNA that signals the termination of translation, indicating that the polypeptide chain is complete.

Transcription Factor: Proteins that help regulate the transcription of specific genes by binding to nearby DNA.

RNA Polymerase: The enzyme responsible for synthesizing RNA from a DNA template during transcription.