4.2.4 Eukaryotic Transcription

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Transcription is the process by which pre-mRNA is synthesised from a DNA template in eukaryotic cells. It involves copying the coding sequence of a gene into a complementary RNA strand.

Steps in Eukaryotic Transcription:

Formation of Pre-mRNA:

DNA is unzipped by RNA polymerase, exposing the template strand (antisense strand).
Free RNA nucleotides pair with complementary bases on the template strand:
Adenine (A) pairs with uracil (U).
Thymine (T) pairs with adenine (A).
Cytosine (C) pairs with guanine (G).
Guanine (G) pairs with cytosine (C).
RNA polymerase catalyses the formation of a single strand of pre-mRNA.

Splicing (Unique to Eukaryotic Cells):

The pre-mRNA contains both introns (non-coding regions) and exons (coding regions).
Introns are removed through a process called splicing, leaving only exons.
The resulting mature mRNA contains the continuous coding sequence required for protein synthesis.

Transport of mRNA:

The mature mRNA exits the nucleus through a nuclear pore.
It travels to the cytoplasm, where it binds to a ribosome to begin the next stage of protein synthesis, translation.

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Key Features of Eukaryotic Transcription:

Pre-mRNA is an intermediate molecule produced before splicing.
Splicing ensures only coding regions (exons) remain in the final mature mRNA.
Introns are non-coding and are removed to ensure the correct amino acid sequence during protein synthesis.
The nuclear envelope allows mRNA to exit the nucleus and interact with ribosomes in the cytoplasm.

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Summary:

In eukaryotic cells, transcription produces pre-mRNA that undergoes splicing to remove introns and form mature mRNA. This mRNA exits the nucleus through a nuclear pore, ready for the next stage: translation.

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