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Multiple Choice
How does the mRNA molecule leave the nucleus after transcription in eukaryotic cells?
A
It diffuses directly through the lipid bilayer of the nuclear membrane.
B
It exits the nucleus via exocytosis.
C
It is transported by ribosomes across the nuclear membrane.
D
It passes through nuclear pores in the nuclear envelope.
Verified step by step guidance
1
Understand the process of transcription: In eukaryotic cells, transcription occurs in the nucleus, where the DNA sequence is used as a template to synthesize a complementary mRNA molecule.
Learn about the nuclear envelope: The nucleus is surrounded by a double membrane called the nuclear envelope, which separates the nuclear contents from the cytoplasm. This envelope contains specialized structures called nuclear pores.
Recognize the role of nuclear pores: Nuclear pores are large protein complexes embedded in the nuclear envelope. They regulate the transport of molecules, including mRNA, between the nucleus and the cytoplasm.
Understand how mRNA exits the nucleus: After transcription, the mRNA molecule is processed (e.g., splicing, addition of a 5' cap, and a poly-A tail) and then passes through the nuclear pores to enter the cytoplasm. This transport is facilitated by specific proteins that guide the mRNA through the pores.
Clarify why other options are incorrect: mRNA does not diffuse directly through the lipid bilayer because the nuclear envelope is impermeable to large molecules. It does not exit via exocytosis, as this process is used for vesicle transport. Ribosomes do not transport mRNA across the nuclear membrane; instead, they translate mRNA into proteins in the cytoplasm.