Questions and Answers
Draw out the pathway for gene expression in eukaryotic cells. What does this large pathway indicate?
Multiple ways and levels from beginning to end to influence gene expression.
What are the two types of RNA?
What is monocistronic mRNA?
It encodes a single polypeptide chain and has a single start site for protein synthesis.
What is polycistronic mRNA?
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Why are prokaryotic RNA processing unique in relation to the generalization that RNA requires processing before it can be used?
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What are the biggest differences in the processes for synthesis of functional mRNA in prokaryotes and eukaryotes?
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What does transcription yield in eukaryotic RNA processing?
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What does pre-mRNA undergo before it can become functional in the cell?
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What is an important distinction between eukaryotic and prokaryotic RNA transport?
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What is the definition of RNA processing and its phases?
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What is splicing?
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What is the 5' cap?
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When does 5' capping occur?
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What does 5' capping protect?
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What is the role of 5' capping in translation?
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What does the 5' capping consist of?
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What are the roles for 5' caps?
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What is eIF4E?
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When would there not be a polyA tail?
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What is the typical length of a polyA tail?
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When is the polyA tail added?
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What is the process and enzyme involved in polyA tail addition?
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What sequence must pre-mRNA have to get a polyA tail?
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What prompts the addition of the polyA tail?
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Outline the polyadenylation process.
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What are the functions of 3' polyadenylation?
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Study Notes
Gene Expression Pathway
- Indicates multiple ways and levels to influence gene expression from start to finish in eukaryotic cells.
Types of RNA
- Monocistronic mRNA: Encodes a single polypeptide chain and has a single start site for protein synthesis; predominant in eukaryotes.
- Polycistronic mRNA: Encodes multiple polypeptide chains, with multiple start and stop signals; found primarily in prokaryotes.
Prokaryotic RNA Processing
- RNA synthesized in a form ready for immediate translation.
- Transcription and translation occur concurrently without membrane separation, influencing one another.
Comparison of mRNA Synthesis in Prokaryotes and Eukaryotes
- Key differences include separation of transcription and translation processes, presence of a 5' cap, polyA tail, and intron removal in eukaryotic mRNA.
Eukaryotic RNA Processing
- Transcription yields a precursor mRNA (pre-mRNA), referred to as a primary transcript.
- Pre-mRNA undergoes chemical changes before becoming functional.
RNA Transport Distinction
- In eukaryotes, transcription and translation are separated by the nuclear membrane.
- RNA processing in the nucleus is required to convert pre-mRNAs to mature mRNAs.
RNA Processing Defined
- Comprises all chemical modifications necessary to mature RNA.
- Phases include:
- 5' cap addition (present in all)
- 3' polyA tail addition (most, at both ends)
- Intron splicing (removal)
Splicing
- Involves hydrolytic removal of non-coding regions (introns) from pre-mRNA.
5' Cap
- Methylated guanosine added at the 7th position on the purine ring.
- Applied shortly after RNA synthesis begins and protects mRNA from degradation by nucleases.
Functions of 5' Cap
- Serves in the initiation of translation by positioning mRNA on ribosomes.
- Involved in signaling proper splicing, regulating ribosome binding, and docking with the nuclear pore during export.
5' Cap and Nuclear Pore Docking
- mRNP (messenger ribonuclear protein complex) packages mRNA for export.
- RNA-binding proteins interact with mRNA, shuttling between nucleus and cytoplasm.
eIF4E
- Eukaryotic initiation factor 4E that binds the 5' cap in the cytoplasm, essential for translation initiation.
PolyA Tail
- Length ranges from 200-250 nucleotides, added to the 3' end after transcription.
- Not encoded by the gene itself, signified by the absence in DNA.
PolyA Tail Addition Process
- Known as 3' polyadenylation, performed by the enzyme poly(A) polymerase, which adds adenines using ATP.
Required Sequence for PolyA Tail
- Pre-mRNA must contain the AAUAAA sequence to initiate tailing.
Polyadenylation Process Steps
- CPSF binds the AAUAAA sequence, forming a stable loop.
- Cleavage occurs 10-35 base pairs downstream, followed by polyadenylation and binding of poly(A) binding proteins for translation stimulation.
Functions of 3' Polyadenylation
- Protects mRNA from nucleases, aids ribosome recognition for translation, facilitates nuclear export of mRNA, and assists in isolating mRNAs in laboratory settings.
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Description
Explore the essential processes of mRNA processing in eukaryotic cells, focusing on the 5' cap and poly (A) tail. This set of flashcards covers critical concepts such as gene expression pathways and types of RNA, enhancing your understanding of molecular biology.