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Unit 6

6.3 Transcription and RNA Processing

#mrna

#rnapolymerase

#nucleotides

#transferrna

#transcription


written by

Samantha Himegarner

samantha himegarner

published on april 3, 2020

Last updated on May 31, 2020

DNA โžก๏ธ RNA

The process of converting DNA into RNA is called transcription. After replication, the Messenger RNA (mRNA) molecules carry the new DNA strand (which will act as a template) from the nucleus to a ribosome. rRNA molecules are what allows the ribosomes to be functional.ย 

๐Ÿงฌ The DNA Strand

The DNA strand acts as the template strand and may also be called a non-coding strand, minus strand, or antisense strand. This is because this strand only serves as a template so that a different strand can be transcribed to match it. The sequence of nucleotides in the single DNA strand is eventually translated into a sequence of amino acids which creates a protein.

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Image courtesy of Flickr.

RNA Molecules

RNA polymerase (an enzyme in the transcription process) synthesizes the mRNA molecule in the 5โ€™ โ†’ 3โ€™ direction as well, and does so by reading the template strand in the opposite direction (3โ€™ โ†’ 5โ€™). Then tRNA molecules bind the amino acids that correlate with the anticodon sequences presented on the mRNA.

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In eukaryotic cells, enzymes modify the mRNA transcript in a few ways:

  1. It can add a Poly-A tail. A few extra adenine nucleotides are added to the 3โ€™ end (hence why it is called a poly-a tail). Poly-A tails are added so that when they are cut or deleted, there is no deletion to the actual code.

  2. It can add a GTP cap.ย A GTP cap (Guanine Triphosphate) is added at the beginning of the strand (the 5โ€™ end) to act as a recognition signal for the ribosome to bind to the mRNA strand.

  3. Alternative Splicing.ย The purpose of splicing is to removeย intronsย and โ€œspliceโ€ theย exonsย together. It essentially deciphers patterns that arenโ€™t necessary (the introns) and removes them. Then, the remaining sections of exons are placed back together.

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