Multiple Choice
After transcription the RNA sequence cannot be changed or modified before translation.
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10. Transcription
RNA Modification and Processing
2:06 minutesProblem 23
Textbook Question
One form of posttranscriptional modification of most eukaryotic pre-mRNAs is the addition of a poly-A sequence at the 3' end. The absence of a poly-A sequence leads to rapid degradation of the transcript. Poly-A sequences of various lengths are also added to many bacterial RNA transcripts where, instead of promoting stability, they enhance degradation. In both cases, RNA secondary structures, stabilizing proteins, or degrading enzymes interact with poly-A sequences. Considering the activities of RNAs, what might be general functions of 3'-polyadenylation?
Verified step by step guidance1
Step 1: Understand the context of 3'-polyadenylation by recognizing that it is a posttranscriptional modification where a sequence of adenine nucleotides (poly-A tail) is added to the 3' end of an RNA molecule, primarily in eukaryotic pre-mRNAs.
Step 2: Identify the role of the poly-A tail in eukaryotes, which generally includes enhancing the stability of the mRNA by protecting it from rapid degradation and aiding in the export of the mRNA from the nucleus to the cytoplasm.
Step 3: Contrast this with the role of polyadenylation in bacteria, where the addition of poly-A sequences often signals RNA degradation rather than stability, highlighting that the function of polyadenylation can differ depending on the organism and context.
Step 4: Consider the interaction of poly-A tails with RNA secondary structures, stabilizing proteins (such as poly-A binding proteins), and degrading enzymes, which collectively influence the fate of the RNA molecule by either protecting it or marking it for degradation.
Step 5: Synthesize these observations to conclude that the general functions of 3'-polyadenylation include regulating RNA stability, influencing RNA processing and transport, and controlling RNA degradation, depending on the cellular context and organism.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
3'-Polyadenylation in Eukaryotic mRNA
In eukaryotes, 3'-polyadenylation involves adding a poly-A tail to the pre-mRNA's 3' end, which enhances mRNA stability, aids nuclear export, and facilitates translation. This tail protects the transcript from rapid degradation by exonucleases and interacts with proteins that regulate mRNA lifespan and function.
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Eukaryotic Transcription
Role of Polyadenylation in Bacterial RNA
Unlike eukaryotes, bacterial RNA polyadenylation often signals RNA degradation. Poly-A tails in bacteria serve as tags that promote the breakdown of defective or unnecessary RNA molecules by recruiting ribonucleases, thus playing a role in RNA quality control and turnover.
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Interactions of Poly-A Sequences with RNA Structures and Proteins
Poly-A tails influence RNA stability and function through interactions with RNA secondary structures, stabilizing proteins, and degrading enzymes. These interactions determine whether the RNA is protected or targeted for degradation, highlighting the dynamic regulation of RNA fate via polyadenylation.
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